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Case Study Questions for Class 8 Science Chapter 11 Force and Pressure

• Last modified on: 1 year ago
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Here we are providing case study questions for CBSE Class 8 Science Chapter 11 Force and Pressure .

Case Study Questions

Question 1:

Read the passage and answer the following questi ons

The discovery of atmospheric pressure gives a fact that air has weight. The weight of the atmosphere presses down on the earth’s surface and creates pressure on it. The pressure at any point exerted by the weight of the air above is called atmospheric pressure. The atmospheric pressure on the earth’s surface at sea level is one hundred thousand pascals i.e., 100 KPa. The atmospheric pressure at a place decrease with an increase in altitude. The atmospheric pressure at a place is the force exerted by the weight of the air column above that place. As we go up the length of the air column above us decreases. This means that its weight and the atmospheric pressure are smaller at higher places than at sea level. If the pressure of the atmosphere is removed suddenly, our blood vessels and tissues will rupture due to the pressure of the blood and other fluids inside. Thus, the spacemen also wear special pressurised suits as in space there is no air and hence, no air pressure. At the top of a mountain, some people can feel their ears “popping” due to a decrease in air pressure. The ears pop to balance the difference in pressure inside and outside the body.

Answer the questions given below:

a) What is atmospheric pressure? b) We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect. Why? c) Why do some people feel their ears “popping” at the top of the mountain?

a) The pressure exerted by the air around us is known as atmospheric pressure.

b) The pressure of the air inside our body is the same as that of the pressure outside. Therefore, we do not experience its effect.

c) Some people feel their ear-popping at the top of the mountain due to the decrease in the air pressure. The ears pop to balance the difference in pressures inside and outside of the body.

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• Force and Pressure Class 8 Case Study Questions Science Chapter 8

Last Updated on May 16, 2024 by XAM CONTENT

Hello students, we are providing case study questions for class 8 science. Case study questions are the new question format that is introduced in CBSE board. The resources for case study questions are very less. So, to help students we have created chapterwise case study questions for class 8 science. In this article, you will find case study questions for cbse class 8 science chapter 8 Force and Pressure.

Table of Contents

Case Study Questions on Force and Pressure

Question 1:

Read the given passage below and answer the question:

In a game of volleyball, players often push the moving ball to their team mates to make a winning move. Sometimes the ball is returned to the other side of the court by pushing or smashing it. In cricket, a batsman plays his or her shot by applying a force on the ball with the bat.

Q.1. What kind of force is applied by a batsman on a ball while hitting it? (a) Magnetic Force (b) Muscular Force (c) Frictional Force (d) Gravitation Force

Difficulty Level: Easy

Ans. Option (b) is correct. Explanation: While hitting a ball, the force is caused by the action of muscles in batsman’s body. The force resulting due to the action of muscles is known as the muscular force.

Q. 2. Force can be defined as: (a) Work done (b) Energy required to do work (c) Push or Pull (d) Push only

Ans. Option (c) is correct. Explanation: A push or a pull on an object is called a force.

Q.3. In the given example of volleyball game, what changes force brought about on the volleyball? (a) Change in direction of motion (b) Change in shape (c) Change in state of motion (d) Both Option (a) and (c)

Ans. Option (a) and (c) Explanation: When players hit the volleyball, its speed changes and also the direction of its motion changes.

Q.4. How do you describe state of motion?

Difficulty Level: Medium

Ans. A change in either the speed of an object, or its direction of motion, or both, is described as a change in its state of motion. The state of rest is considered to be the state of zero speed. An object may be at rest or in motion; both are its states of motion.

Q. 5. Give two examples showing that force has brought about change in shape of an object.

Ans. 1. Pressing a ball of dough by roller pin to make chapati. 2. Stretching a rubber band.

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• Learn the basic concept of force.
• Understand the various facets of force.
• Learn about the different changes that are due to the application of force.
• Learn different types of forces.
• Understand the concept of pressure.
• Learn about pressure exerted by liquids and gases (atmospheric pressure).

A push or pull on an object is known as force. Force can be of two types: Contact Force and Non-Contact Force. Force per unit area is called pressure. Liquids and gases exert pressure on the walls of their containers. The pressure exerted by air around us is known as atmospheric pressure. This chapter deals with force and pressure.

Frequently Asked Questions (FAQs) on Force and Pressure Case Study Questions

Q1: what are case study questions for cbse examinations.

A1: Case study questions in CBSE examinations typically involve scenarios or real-life examples, requiring students to apply their understanding of concepts to solve problems or analyze situations.

Q2: Why are case study questions important for understanding class 8 science chapters?

A2: Case study questions provide a practical context for students to apply theoretical knowledge to real-world situations, fostering deeper understanding and critical thinking skills.

Q3: How should students approach answering case study questions for CBSE?

A3: Students should carefully read the case study, identify the key issues or problems presented, analyze the information provided, apply relevant concepts and principles of force and pressure, and formulate well-supported solutions or responses.

Q4: Are there any resources available online for students to practice case study questions on class 8 science chapters for CBSE exams?

A4: Yes, several educational websites offer case study questions for CBSE students preparing for science examinations. We also offer a collection of case study questions for all classes and subject on our website. Visit our  website  to access these questions and enhance your learning experience.

Q5: How can students effectively prepare for case study questions on force and pressure for CBSE exams?

A5: Effective preparation strategies include regular revision of concepts, solving practice questions, analyzing case studies from previous exams, seeking clarification on doubts, and consulting with teachers or peers for guidance and support.

Q6: How can teachers incorporate case study questions on force and pressure class 8 science into classroom teaching?

A6: Teachers can integrate case studies into lesson plans, group discussions, or interactive activities to engage students in active learning, promote problem-solving skills, and facilitate a deeper understanding of force and pressure concepts.

Q7: Can the attraction and repulsion between two magnets be termed as application of force in between them?

A7: Yes, attraction and repulsion between two magnets is push and pull due to application of magnetic force.

Q8: Define pressure.

A8: The force acting on a unit area of a surface is called pressure.

Q9: Why does a balloon or a cycle tyre increase in size and become stiff when air is filled in them?

A9: When air is filled in balloons or cycle tyre, the air molecules start exerting pressure on the walls of balloon or tyre, thus their size increases and they become stiff.

Q10: Differentiate between contact forces and non-contact forces. Give two examples of each.

A10: Contact forces are those forces that need to be in contact of the object to show its effect. Example, Muscular Force and Frictional Force. Non-contact forces are those that can be applied without being in contact with the object. Example, Electrostatic and Magnetic Forces.

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Important Questions Class 8 Science Chapter 11

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Important Questions Class 8 Science Chapter 11 – Force and Pressure

Science is a very important subject taught in school. It helps us  solve all real-life problems with logic and clarity. In this chapter, students will study force and pressure. 

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In physics, the force can be defined as an influence that changes an object’s motion. The force can be applied from outside of an object, or it can be an internal influence. On the other hand, pressure is the force applied perpendicularly to every unit of an area. Thus, the pressure depends on the force and the area.  Students must spend as much time as possible practising the chapter’s questions.

Extramarks is a leading company that provides all the important study materials. Our experts have made the Important Questions Class 8 Science Chapter 11 to help students in practice. They collected the questions from different sources, such as the textbook exercises, CBSE sample papers, CBSE past years’ question papers, and important reference books. They have solved the questions too. Thus, this article will help students to score better on exams.

Extramarks is a very reputed company in India, and we provide all the necessary study materials related to CBSE and NCERT. You can download these study materials after registering on our official website. You will find the CBSE syllabus, CBSE past years’ question papers, CBSE sample papers, CBSE extra questions, CBSE revision notes, NCERT books, NCERT important questions, NCERT solutions, NCERT Exemplar, vital formulas, and many more.

Get Access to CBSE Class 8 Science Important Questions 2022-23 with Chapter-Wise Solutions

You can also find CBSE Class 8 Science Chapter-by-Chapter Important Questions here:

Important Questions Class 8 Science Chapter 11 – With Solutions

Extramarks is a leading company that provides all the important study materials. Our experts have made this question series after collecting suitable questions from different sources. They have accumulated the questions from the textbook exercises, CBSE sample papers, CBSE past years’ question papers, important reference books, and NCERT exemplars. They have also solved the questions, and experienced professionals have further checked the answers to ensure the best quality of the content. Thus, the Important Questions Class 8 Science Chapter 11 will help students  score better in exams. The important questions are-

Question 1. Give any two examples of each situation where you push or pull to change the state of motion of the objects.

Examples of  situations where you push or pull to change the state of the motion of objects.

• The Pull situations are- 
• i) In order to open a drawer, we will eventually have to pull it. This action results in a change in the state of motion of the drawer.
• ii) To draw water from a well, the rope is pulled by applying force. This action results in a change in the state of motion of the bucket.
• The Push Situations are
• i) A football is pushed by the foot of a player. This action results in a change in the state of motion of the ball.
• ii) To move the heavy box from one room to another, we will need to push it.This action results in a change in the motion of the box.

  Question 2. Give any two examples of situations in which the applied force causes a major change in the shape of an object.

The forces that change the shape of the object are as follows:

• i) By pressing the clay between our hands, it deforms.
• ii) The shape of the plastic bottle also changes by squeezing it.

Question 3. An archer stretches her bow while taking aim at a target. She then releases the arrow, which then begins to move towards the target. Based on the above information, fill in the gaps in the following statements using these terms.

muscular, contact, noncontact, gravity, friction, shape, and attraction

(i) The Archer applies force to stretch the bow. This force causes a change in its __________.

(ii) The Archer applies force to stretch the bow. The force applied is an example of __________ force.

(iii) The type of force that is responsible for a change in the state of the arrow’s motion is an example of a __________ force.

(iv) While the arrow moves towards its target, the forces acting on it result from __________ and from __________ of air.

(i)The Archer applies a force to stretch the bow. This force causes a change in its shape.

(ii)The Archer applies a force to stretch the bow. The force applied is an example of muscular force.

(iii) The type of force that is responsible for a change in the state of the motion of the arrow is an example of the contact force.

(iv) While the arrow moves towards its intended target, the forces acting on it result from gravity and from the friction of the air.

Question 4. In the following situations, identify the agent that exerts the force and the object on which it acts. Also, state the effect of the force in each case.

(i) Squeezing a lemon between your fingers to extract lemon juice

(ii) Taking out paste from a toothpaste tube.

(iii) A load that is suspended from a spring while its other end is attached to a hook fixed to a wall.

(iv) An athlete making a high jump to clear the bar at a certain height

• i) We use muscular force to extract the juice of a lemon by squeezing it between the fingers. As a result, the shape of the lemon changes.
• ii) To take out the paste from the toothpaste tube, we use muscular force. This muscular force acts on the toothpaste tube, leading to a change in its shape.

iii) Here, the suspended load exerts a force on the spring, which results in pushing the spring downwards. As a result, the spring gets stretched. Hence, its shape changes.

• iv) The feet of the athlete exert a muscular force on the ground, which then pushes the ground. This force then allows him to jump over the bar. As a result, the state of motion gets changed.

Question 5. While making a tool, a blacksmith hammers the tool with a hot piece of iron. How does the force involved in the hammering affect this piece of iron?

When hammering a hot piece of iron, a blacksmith uses muscular force. This muscular force results in the changing of the shape of the hot iron so that it can result in the desired shape.

Question 6. An inflated balloon is pressed against the wall after being rubbed with a piece of synthetic cloth. It was found that after rubbing the balloon, it stuck to the wall. What force is responsible for the attraction that is between the balloon and the wall?

When an inflated balloon is rubbed together with a piece of synthetic cloth, the balloon becomes charged. And a charged body always attracts an uncharged body. So, when this charged balloon is pressed against a wall, it sticks to the wall. Thus, an electrostatic force is generated that acts between the charged balloon and the wall.

Question 7. Name the forces that act on a plastic bucket containing water that is held above ground level in your hand. Also, discuss why these forces acting on the bucket do not bring about a change in its state of motion.

To hold these buckets of water above the ground, we have to use muscular force. Now, this muscular force acts against the force of gravity (gravitational force) that pulls the bucket towards the ground. Hence, the two forces are equal in magnitude but opposite in direction. Hence, the net force applied to the bucket is zero. Also, there is no change in the state of motion.

Question 8. . A rocket has been fired upwards in the sky to launch a satellite in its orbit. Name the two forces that act on the rocket immediately after it leaves the launching pad.

The force of gravity (gravitational force) is one of the forces that act on the rocket, and it tries to pull it towards the ground, while the other one is the force of friction applied due to the earth’s atmosphere, which opposes its motion.

Question 9. When we press the bulb of the dropper with its nozzle, which is kept in the water, the air present in the dropper is seen to escape in the form of water bubbles. And once we release the pressure on the bulb of the dropper, water gets filled in the dropper. This rise in dropper water is caused by

(i) the pressure of water.

(ii) gravity of the earth.

(iii) shape of a rubber bulb.

(iv) Atmospheric Pressure

Option iv is the right answer.  

Explanation- The amount of water in the dropper increases due to atmospheric pressure.

When all the air escapes from the dropper’s nozzle by applying pressure, the atmospheric pressure then acts on the water forces the water in an upward direction and fills the nozzle of the dropper.

Question 10. During the dry weather, while combing our hair, we sometimes experience hair flying apart. The force responsible for this is

(i) force of gravity.

(ii) electrostatic force.

(iii) the force of friction.

(iv) magnetic force.

The correct answer is (ii) electrostatic force.

Explanation:

On combing our hair, the comb and hair get oppositely charged due to electrostatic force.

Question 11. Two objects repel each other. This force of repulsion could be due to

(i) frictional force only

(ii) electrostatic force only

(iii) magnetic force only

(iv) either a magnetic or an electrostatic force

The correct answer is option (iv), either a magnetic force or an electrostatic force.

Explanation: when two objects are simultaneously experiencing repulsive force, this can be because there may be a presence of an electrostatic force or a magnetic force.

Question 12. Which one of the following forces is a contact force?

(i) force of gravity

(ii) force of friction

(iii) magnetic force

(iv) electrostatic force

The correct answer is (ii) the force of friction.

Explanation :

The force of attraction acts only when these bodies are in contact with each other.

Question 13. Two persons are applying forces to the two opposite sides of a moving cart. The cart still moves after applying the force, with the same speed and in the same direction. What do you understand from the above case about the magnitudes and directions of the forces applied?

The force applied is of equal magnitude in the opposite directions; hence, the cart moves forward at the same speed in the same direction.

Question 14. Two thermocouple balls are held close to each other, and after some time, When they are released, they move away from each other. Name the force that will be responsible for the above phenomenon. Explain it in brief.

Two thermocouple balls are held close to each other, and after some time, when they are released, they move away from each other because of the electrostatic force. The balls having similar charges move away due to the repulsion force acting between similar charges.

Question 15 . An archer horizontally shoots an arrow in the air. However, after flying some distance, the arrow falls to the surface. Name the initial force that acted and set the arrow in motion. Also, explain why the arrow falls down.

The Archer uses muscular force to stretch the string. This muscular force will change the shape of the arrow. When the string that released the arrow regains its original position, the original position is the one that gives it the initial force to set the motion. The arrow falls down because of the gravitational force through which it comes down after some time.

Question 16. It is difficult to cut cloth with scissors that have blunt blades. Explain in brief.

The blunt blade has a larger area as compared to the shard-edged blades. Because of this, the blunt-blade scissors produce low pressure, which makes it difficult to cut the cloth. On the other hand, in a sharp blade, the surface area is much smaller, which in turn increases the pressure produced. This increased pressure makes cutting the cloth easier with sharp blades.

Question 17. Two women are of the same weight. One of them wears sandals with pointed heels, while the other woman wears sandals with flat soles. Which one of them would feel more comfortable while walking on a sandy beach? Also, give reasons for your answer.

Although both women’s heights are the same, they also carry the same weight when they walk. But the woman wearing the sandal with flat heels will be more comfortable than the woman wearing sandals with pointed heels while walking on a sandy beach. This is because the flat soles have a larger surface area as compared to sandals with pointed heels. 

Also, the pressure exerted by the woman with pointed heels will be greater as compared to that of the woman wearing sandals with flat soles. 

This increased pressure will make walking on sand in sandals with pointed soles difficult.

  Question 18 . It is much easier to burst an inflated balloon with a needle than with a finger. Explain why.

 It is easier to burst an inflated balloon with a needle rather than with a finger because the pressure exerted on the inflated balloon by a needle will be more as compared to the finger. This larger pressure is due to the smaller area of contact, and so this pressure pierces the surface of the balloon easily, which then makes it burst.

Question 19. A chapati maker is a machine that converts small balls of dough into round chapati. What effect does force have in this process?

Answer 19: The force that comes into play in this process is called pressure.  Hence, the pressure exerted by the chapati maker on the dough converts the small balls of the dough into chapatis.

Question 20. Fruits that get detached from a tree fall due to the force of gravity. We know that this force arises due to the interaction between two different objects. Name the objects interacting in the above case.

Answer 20: Earth and the fruit are the interacting objects in the above case. The force of gravity is applied by the earth to the fruit. Hence, that is why it falls down. 

Question 21. Discuss contact and non-contact forces briefly.

Answer 20. Contact Forces are-

• a) Muscular Forces: Muscular Force is the force that is caused by the muscular power of a human being or an animal on any object. It occurs when the object is in contact with the body that is applying the force.

b)Friction: It is applied by the surface in resistance to the motion of an object over it.

Noncontact Forces are-

• a) Magnetic Force: Magnetic Force is the force exerted by the two magnets that can move toward or against each other. It can exist between the magnet and the magnetic object. Hence, this is known as a magnetic force.
• b) Electrostatic Force: The force applied by a charged body to another charged or uncharged body is called electrostatic force.
• c) Gravitational Force: An attractive force between objects that depends on the mass of two bodies is called Gravitational Force.

Question 22. What is force?

In Science, when an object gets displaced or tends to get displaced from its original position, it requires an external agent to do the work. This external agent is called a force. It is of two different types: push force and pull force. Also, force is a vector quantity that has both magnitude and direction.

Question 23. What Can a Force Do?

Answer 23- 

It can also change the state of the motion of an object.

It can also change the direction of an object.

It can also change the shape of an object. 

Question 24. What do you mean by “friction”?

Friction is the kind of force that is actually responsible for changing any kind of state of motion. For example, when an object slides on a smooth surface, the friction generated is less than when the object slides on a rough surface.

Question 25 . What is Pressure?

The pressure on an object is defined as the force which is acting on its square unit surface area. 

Pressure = Force divided by the area of the surface

Its unit is newton per m2. Atmospheric pressure is defined as the pressure of the air around us.

Question 26 . Do Liquids and Gases Exert Pressure on the Surface?

Yes, both liquids and gases exert pressure on the surface. It can also be understood with an example. If we fill a balloon with either water or air, then after a certain amount of time, the balloon bursts. This is because of the pressure that is exerted by air or water on the surface of the balloon.  

Question 27. When a force applied to an object is equal and opposite in nature, then this force will

• a) May move the object.
• b) Change the shape of an object and may move the object.
• c) May stop a moving object.
• d) Do not move the object but it can cause a change in its shape.

Answer 27: Option d is the correct answer.

Explanation. 

It will not move the object but will cause a change in its shape.

Question 28. Find out the type of force that is acting in the below situations.

• a) A coin or a pen falls down to the ground when it gets slipped out of hand.

Answer: The Gravitational Force acts when a coin or a pen falls to the ground when it slips out of your hand.

• b) A boat comes to rest when someone stops rowing it.

Answer: Due to friction, a boat comes to rest when someone stops rowing it.

c)When a person lifts a heavy bucket of water.

Answer: Muscular Force acts when a person lifts a heavy bucket of water.

Question 29 . Describe the state of motion of an object briefly.

Answer 29: The motion of any object is always defined by its speed and direction. The resting state is always considered to be the state of zero speed. An object may be at rest or in motion; these are its two states of motion.

Question 30. Explain briefly why a ball rolling along the ground gradually slows down and comes to rest.

Answer 30: A ball rolling along the ground always gradually slows down and comes to rest because of friction. In the above case, the frictional force acts between the surface of the ball and the ground and acts opposite to the direction of the motion, which eventually brings the ball to rest after some time.

Question 31. Explain why the porters place a round piece of cloth on their heads whenever they have to carry heavy loads. 

Answer 31: Porters place a round piece of cloth on their heads whenever they have to carry heavy loads because, by using this method, their area of contact with the load increases and the pressure on their heads decreases. since the pressure is inversely proportional to the area of contact on their head. This makes it easier for the porters to carry heavy loads.

Question 32. What type of force is friction – a contact or a noncontact force? Why?

Answer 32: Friction is termed “contact force” because it arises due to contact between two surfaces. While rubbing against each other, the contact surface exhibited frictional motion. This frictional force always acts in the direction that is opposite to the direction of the motion.

Question 33. Do you think that sometimes the application of force does not result in a change in the state of motion? Describe this with an example.

 Sometimes the application of force does not result in a steady change in the state of motion. This, however, does not mean that the force is not applied; instead, it means that the force that is applied is not enough to result in a change in the state of motion, i.e., move the object.

  For example, imagine applying specific pressure to a wall or a heavy stone and it not moving.

Question 34. What are the effects of the application of force on the object? Explain it in brief.

Answer 34:  

The effects of the application of force on the object are as follows:

• The shape of an object can be changed.

For example, a cricket ball changes shape temporarily when it is hit by a bat.

• The direction of a moving object can also be changed.

 For example, the direction of the cricket ball also changes when it is hit by the bat.

iii. A moving object can be easily brought to rest.

 For example, putting a hand in front of the rolling ball will bring it to rest.

• A stationary object can easily be brought to motion.

For example, rolling a stationary ball on a flat surface can easily set it in motion.

• It can change the speed of an object.

For example, further pushing a rolling ball on the surface in the same direction as its motion results in an increase in its speed.

Question 35. Demonstrate an experiment to show that the liquids exert pressure on the walls of the container.

Answer 35:  To show that the liquids exert pressure on the walls of the container in which they are filled. We start with a plastic bottle and then attach a few centimetres long cylindrical glass tube near the bottom of the bottle.To do this, you can first simply heat one end of the glass tube and then immediately insert it near the bottom of the plastic bottle. Now, seal any leakage, if present, with molten wax. And then, cover the open end of the glass tube with a thin rubber sheet. Afterwards, fill half of the plastic bottle with water.

Also, note that the rubber sheet bulges out, which happens due to the pressure that is applied by water. The above experiment proves that the liquids exert pressure on the walls of the container.

Benefits of Solving Important Questions Class 8 Science Chapter 11

Practice is very important for students to score better in exams. It helps them in many ways, like increasing their confidence, and generating interest in the subject matter, among other things. So, students must take help from other books to solve questions regularly, which will help them become better at the subject. There will be multiple benefits to solving the important Questions Class 8 Science Chapter 11. These are-

• The experts of Extramarks identify the importance of practice. They have collected the questions from different sources so students can solve them regularly. They have collated the questions from the textbook exercises, CBSE sample papers, important reference books, and NCERT Exemplars. They have also included a few questions from previous years’ CBSE question papers so that students are aware of possible exam questions. Thus, the Important Questions Class 8 Science Chapter 11 will provide them with a wide range of questions and help them boost their confidence.
• The experts have not only collected the questions  but have also provided the answers. They have solved each of the questions, and students can follow the solutions if they cannot solve any question. They can also check their answers with the answers provided by the experts. Furthermore, experienced professionals have further checked the answers to ensure the best quality of the content. As a result, the Chapter 11 Important Questions for Class 8 Science will also assist them in answering various types of questions, allowing students to feel more confident about the subject matter.
• Many students tend to be afraid of science. They may require assistance in comprehending the subject matter or clarification of their doubts
• Science is a very interesting subject, and one must practise more and more to build their concepts. The experts have taken care of this fact as well. This is why they have not only collected the questions but also provided the answers. Thus, students can follow the solutions, and their doubts get answered. So, the Science Class 8 Chapter 11 Important Questions will guide the students to build their concepts strongly, and they can be interested in the subject matter. Thus, this article will also help them boost their confidence and better prepare for the exams.

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Q.1 What are the characteristics of the image formed by a plane mirror How is the position of the image related to the position of the object

Marks: 5 Ans

Characteristics of the image formed by a plane mirror: (i) It is virtual. (ii) It is always erect. (iii) It is of the size of the object. (iv) The image is formed as far behind the mirror as the object is in front of it. (v) The image is laterally inverted. (vi) Image is situated on the perpendicular drawn from the object to the mirror. The position of the image is at the same distance behind the mirror as the object is in front of it. If the object is shifted by a distance d towards the mirror, the image will also shift by the same distance d towards the mirror, i.e., the separation between the object and image will decrease by 2d.

Q.2 Define reflection of light. Name the types of reflection.

Marks: 1 Ans

The return of light into the same medium after striking a surface is called reflection.

There are usually two kinds of reflection:

(i) Regular reflection. (ii) Irregular reflection.

Q.3 Define dispersion of light.

Marks: 2 Ans

The splitting of white light into seven colours on passing through a transparent medium, like a glass prism is called dispersion of light.

Q.4 What is a cataract How this defect can be removed

A cataract is an eye defect that usually occurs in old age. In this eye defect, eyesight becomes foggy because the eye lens becomes cloudy. There is a loss of vision. This defect can be treated when the opaque lens is removed and the new artificial lens is inserted.

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Cbse class 8 science important questions, chapter 1 - crop production and management.

Chapter 2 - Microorganisms : Friend and Foe

Chapter 3 - synthetic fibres and plastics, chapter 4 - materials : metals and non-metals, chapter 5 - coal and petroleum, chapter 6 - combustion and flame, chapter 7 - conservation of plants and animals, chapter 8 - cell - structure and functions, chapter 9 - reproduction in animals, chapter 10 - reaching the age of adolescence, chapter 12 - friction, chapter 13 - sound, chapter 14 - chemical effects of electric current, chapter 15 - some natural phenomena, chapter 16 - light, chapter 17 - stars and the solar system, chapter 18 - pollution of air and water, faqs (frequently asked questions), 1. how can the important questions class 8 science chapter 11 help students.

Extramarks is a leading company that provides all the important study materials related to CBSE and NCERT. Our experts created important questions to assist students in practice. They have collected the questions from CBSE sample papers, CBSE past years’ question papers, important reference books, and textbook exercises. Thus, students can search for questions in different sources, but they will find them in the Important Questions Class 8 Science Chapter 11. Furthermore, the experts have solved the questions, and experienced professionals have further checked the answers. Thus, the question series will help students score better on exams. It will also help them generate interest in the subject matter.

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Force and Pressure Class 8 Important Questions and Answers

Important questions of Class 8 Science Chapter 11 Force and Pressure is given below. These important questions will help students while preparing for the exam.  Practising these important questions will analyse their performance and work on their weak points. Score well in exam of Class 8 Science by going through these important questions. Students of Class 8 can download important questions of Class 8 Science Chapter 11 Force and Pressure PDF by clicking the link provided below.

Important Questions of Class 8 Science Chapter 11 Force and Pressure

Here you can get  Class 8 Important Questions Science  based on NCERT Text book for Class 8. Science Class 8 Important Questions are very helpful to score high marks in board exams. Here we have covered Important Questions on  Force and Pressure  for Class 8 Science subject.

Very Short Answer Questions

1. How can we decide whether an object is moving faster than the other? Answer:  By their speed.

2. What is the distance moved by an object in unit time called? Answer:  Speed.

3. How can we change the speed and the direction of a moving body? Answer:  By applying force.

4. What is force? Answer:  A push or a pull on an object is called force.

5. What is the requirement for a force to come into play? Answer:  Interaction between two objects is required for a force to come into play.

6. What is the resultant force when two forces act in same direction? Answer:  Forces applied on an object in the same direction add to one another.

7. What will be the resultant force when two forces act in opposite directions on an object? Answer:  When two forces act in opposite directions on an object then the net force will be the difference between two forces.

8. What happens in a tug of war when two teams pull equally hard? Answer:  When two teams pull equally hard then the rope does not move in any direction.

9. Name the term used to express the strength of a force. Answer: Magnitude.

10. When does the net force become zero? Answer:  When two forces acting on an object in opposite directions are equal then the net force becomes zero.

11. A ball is at rest. Push it gently. Does the ball begin to move? Answer:  Yes, the ball begins to move.

12. What happens when we push again while the ball is moving? Answer:  When we push a moving ball, then its speed increases.

13. Place your palm in front of a moving ball. Does your palm apply any force on the ball? Answer:  Yes, our palm applies a force on the ball.

14. What happens to the speed of the ball when you place your palm in front of the moving ball? Answer:  The speed of the ball is decreased.

15. What are the two states of motion? Answer:  There are two states of motion: (i) The state of rest (ii) The state of motion.

16. Does the application of a force would always result in the change in the state of motion of an object? Answer:  No, it does not always change the state of motion of an object.

17. What is muscular force? Answer:  The force resulting due to the action of muscles is known as muscular force.

18. Give two examples of muscular force. Answer:  Bending of our body and kicking the ball.

19. Does the force can change the speed of a moving object? Answer:  Yes.

20. What effect does a force put on the shape of an object? Answer:  The force may cause change in shape of the object

21. Is muscular force a type of contact force? Answer:  Yes, muscular force is a type of contact force.

22. What is force of friction? Answer:  The force which acts on all moving objects in opposite direction to the motion of the body is called force of friction.

23. What kind of force is friction? Answer:  Force of friction is also a type of contact force.

24. Why is force of friction called contact force? Answer:  Since the force of friction arises due to contact between surfaces of moving body and other surfaces, so it is called a contact force.

25. Give two examples of contact forces. Answer:  (i) Muscular force (ii) Force of friction

26. What are non-contact forces? Answer:  The forces acting from a distance without making contact are called non-contact forces.

27. Give an example of a non-contact force. Answer:  Magnetic force.

28. What is magnetic force? Answer:  The force exerted by a magnet on any magnetic object is called magnetic force.

29. What are the interaction of poles of two magnets? Answer:  (i) Like poles repel each other. (ii) Unlike poles attract each other.

30. What do you mean by electrostatic force? Answer:  The force exerted by a charged body on another charged or non-charged body is called electrostatic force.

31. What kind of force is an electrostatic force? Answer:  It is non-contact force.

32. What is gravitational force? Answer:  The force by which earth or any other object attracts objects towards itself is called the gravitational force.

33. Is the gravity a property of earth only? Answer:  No, gravity is not a property of earth only.

34. Is the gravitational force a contact or non-contact force? Answer:  The gravitational force is non-contact force.

35. Name the force due to which every object falls on the earth. Answer:  Due to gravitational force.

36. What do you mean by pressure? Answer:  The force acting on a unit area of a surface is called pressure. Pressure = Force/Area

37. How can we increase the pressure by exerting same force? Answer:  To increase pressure we should exert the same force on a smaller area.

38. Do liquids and gases also exert pressure? Answer:  Yes, liquids and gases also exert pressure.

39. What is the site of the pressure exerted by a liquid on the container? Answer:  A liquid exerts pressure on the walls of the container.

40. Do gases also exert pressure on the walls of containers? Answer:  Yes, gases also exert pressure on the walls of the containers.

41. What is atmosphere? Answer:  The envelop of air around us is called atmosphere.

42. What is atmospheric pressure? Answer:  The pressure exerted by the air is known as atmospheric pressure.

43. Can you separate two hemispheres, if all the air is suck out from them? Answer:  There is no air inside the two hemispheres, so only outer surface is in contact of atmospheric pressure. This is because we cannot separate them.

Short Answer Type Questions

1: What is force? What is its unit?

Answer:  A push or a pull on an object is called a force. It arises due to the interaction between two objects. Force has magnitude as well as direction. It may change in the state of motion of an object or it may bring about a change in the shape of an object. The unit of force is Newton.

2: What is change in state of motion? What brings change in state of motion?

Answer:  A change in either the speed of an object, or its direction of motion, or both, is described as a change in its state of motion. Force may bring the change in the state of motion of an object.

3: What is the difference between contact forces and non-contact forces? 

Answer:  Forces which act only when there is physical contact between two interacting objects are known as Contact forces. Example: Muscular force. Whereas Forces which can act without physical contact between objects i.e. those that can act from a distance, are called non-contact forces or field forces. Example: Magnetic force.

4: Give two example each of the situation in which you apply force to change state of motion of an object and to change shape of an object?

Answer:  A goal keeper applies force for saving a goal. By his action the goal keeper tries to apply a force on the moving ball. This leads to change in state of motion of ball. Force is applied to the shape of a ball of dough when it is rolled to make a chapatti.

5: Why is it difficult to hold a school bag having a strap made of a thin and strong string?

Answer:  It is difficult to hold a school bag having a strap made of a thin and strong string because it apply the large pressure on the shoulders due to very small contact surface area. The pressure is inversely proportional to the surface area on which the force acts. Therefore, pressure decreases if surface area increases.

6: Why Porters wear turbans when they have to carry heavy loads on their heads?

Answer:  Porters wear turbans when they have to carry heavy loads on their heads, to increase the area of contact. This reduces the pressure on the head.

7: Force applied on an object may change its speed. How?

Answer:   force applied on an object may change its speed. If the force applied on the object is in the direction of its motion, the speed of the object increases. If the force is applied in the direction opposite to the direction of motion, then it results in a decrease in the speed of the object

8: Why Lorries and trucks carrying heavy loads have 8 tyres instead of four?

Answer:  Lorries and trucks carrying heavy loads have 8 tyres instead of four. Also the tyres are broader because this increases the area of contact with the ground, thus reducing the pressure exerted on the ground.

9: Why the sucker sticks to the surface over which it is pressed?

Answer:  When we press the sucker, most of the air between its cup and the surface escapes out. The sucker sticks to the surface because pressure of atmosphere acts on it. To pull the sucker off the surface, the applied force should be large enough to overcome the atmospheric pressure.

10: What is pressure? How is pressure related to the surface area on which it acts?

Answer:  Force per unit area is called pressure. Pressure is inversely proportional to the surface area on which it acts. Smaller the area, larger the pressure on the surface for the same force.

11: When we stop pedalling the bicycle, it slows down and gradually stops .Why?

Answer:  When we stop pedalling the bicycle, it slows down and gradually stops because of force of friction between the surface of tyres of cycle and the ground that brings moving bicycle to rest. The direction of force of friction is always opposite to the direction of motion.

12: What is frictional force? How it arises?

Answer:  The force acting against the relative motion of surfaces in contact is called frictional force or friction. Friction is an example of contact force. Force of friction arises due to contact between surfaces.

13: What is magnetic force? What happens when we bring like poles of two magnets closer?

Answer:   A magnet can exert force on another magnet without being in contact with it; this force is known as magnetic force. Like poles of two magnets repel each other. Unlike poles of two magnets attract each other.

14: What is gravitational force? Is gravity the property of earth alone?

Answer:   Every object exerts a force on every other object. This force is known as gravitational force. Gravity is not a property of the earth alone. Every object in the universe whether large or small exerts gravitational force on every other object.

15: A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket just after leaving of the launching pad

Answer:   The force acting on a rocket is:

• Frictional force due to air
• Force of gravity acting in downward direction.

16: What will be the effect of force while squeezing a piece of lemon between the fingers?  

Answer:  Agent exerting pressure: Fingers. Object: Lemon. Effect of force is observed: Lemon juice is coming out, change in shape of lemon.

17: What will be the effect of force while taking out toothpaste from toothpaste tube?

Answer:  Agent exerting pressure: Fingers. Object: Tooth paste tube Effect of force is observed: Tooth paste is coming out, change in shape of tooth paste.

18: A blacksmith is hammering a hot piece of copper for making a tool, how does the force due to affect the piece of copper? 

Answer:  The force due to hammering changes the shape of the hot piece of copper to make tools.

19: What are the effects of the force while making high jump by an athlete?

Answer:  Agent exerting pressure: An athlete. Object: Body Effect of force: Jumping

20: Differentiate between atmosphere and atmospheric pressure.

Answer:  Atmosphere is the envelope of air surrounding our earth but the atmospheric pressure is the pressure exerted by this air.

21: Differentiate between friction and contact force.

Answer:   Friction is the force responsible for changing the state of motion of objects but contact force is the forces which act only when there is physical contact between two interacting objects.

22: What is a force? Explain with the help of some examples.

Answer:  Force is a pull or push of the objects. The action like, pushing, pulling, picking, hitting, lifting, running and bending are the examples of force. Moving or stopping of a body, changing shape and direction of motion of objects are various actions which show force in play.

23: How do we feel force in our daily life?

Answer:  Various big or small actions make us feel the force. We hit or catch many objects in our daily life. We see that a moving ball stops on its own. The ball changes the direction of its motion when it is hit with a bat. We make lassi etc. by churning of curd. These are many actions which help us to feel that a force is exerted.

24: Explain that forces are due to an interaction between objects.

Answer:  Imagine, a man is standing behind a stationary car. The car does not move due to his presence.

Now allow the man to push the car, it means he applies a force on the car. The car may begin to move in the direction of the applied force. Note that the man has to push the car to make it move. This example shows that at least two objects must interact with each other for a force to come into play.

25: What happens when (i) Two forces are exerted in same direction? (ii) Two forces are exerted in opposite directions?

Answer:  (i) When two forces are exerted in same direction on an object, then the forces are added and action becomes easy. (ii) When two forces act in the opposite directions on an object, the net force acting on it is the difference between the two forces.

26: What are the two factors on which effect of force depends?

Answer:  There are following two factors on which the effect of force depends: (i) Magnitude:  The strength of force is usually expressed by its magnitude. (ii) Direction of force:  We have also to specify the direction of force in which it acts. If the direction or magnitude of force changes, its effect also changes.

27: What are the effects of force?

Answer:  A force changes or try to change the (i) Speed of a moving body. (ii) Direction of motion of a body. (iii) Shape of a body.

28: What are states of motion?

Answer:  An object can be in two positions, one is at rest or other in motion ; both are its states of motion. Any change in this position (rest or motion) can be called the change in the state of motion. The state of motion of an object is described by its speed and the direction of motion.

29: How can a force change the states of motion?

Answer:  There are two states of an object: (i) Rest (ii) Motion When a force is applied on a body then it can move. In the same way a force can change the direction of a moving object as well as its speed. A force can stop a moving object. If the force is applied in the direction of motion at an object, then its speed is increased. If the force acts in opposite direction, then the speed of the object is decreased.

30: What is the effect of force on the shape of an object?

Answer:  A force can change or try to change the shape of an object. When a force is applied on an object then change in shape takes place. It may be smaller or greater. At last we can say that the application of force on an object may change its shape.

31: Explain contact and non-contact forces.

Answer:  Contact forces: The forces which come into play only when two objects come in contact with each other are called contact forces. Muscular force and force of friction are the examples of contact forces. Non-contact forces: The forces which come into play without any contact of objects with one another are called non-contact forces. Electrostatic and magnetic forces are the examples of non-contact forces.

32: What is muscular force? Why is it called contact force?

Answer:  The force resulting due to the action of muscles is known as the muscular force. Muscular force is called contact force because it comes in action only when two bodies come in contact with each other.

33: What do you understand by the force of friction?

Answer:  The force which always acts on all the moving objects and whose direction is always opposite to the direction of motion is called force of friction. Since the force of friction arises due to contact between surfaces, it is also called contact force.

34: What is electrostatic force? Why is it called non-contact force?

Answer:  The force exerted by a charged body on another charged or uncharged body is called electrostatic force. This force comes into play even when the bodies are not in contact, so it is called non-contact force.

35: Explain force of gravity.

Answer:  Objects or the things that fall towards the earth because the earth pulls them. This force is called force of gravity or the force due to gravitation. This is also called just gravity. It is an attractive force. This force acts on all objects.

36: What is pressure? What happens to the pressure when area on which it is applied increases?

Answer:  The force acting on a unit area of a surface is called pressure. Pressure = Force/Area on which it acts. The pressure is inversely proportional to the area on which force is applied. As the area on which force is applied is increased, the pressure decreases. We can say that pressure increases with decrease in area.

37: We observe that the wheels of buses and trucks are heavier than the wheels of cars or scooters. Why?

Answer:  The buses and trucks are heavy and require to exert less pressure. We know that pressure decreases as area of contact increases, so the tyres are broadened so that they exert less pressure on earth and move easily. If they exert more pressure, they will sink in earth. The scooters and cars have less wide wheels because they need more pressure for gripping.

38: What is atmospheric pressure?

Answer:  The envelop of air around the earth is known as atmosphere. The atmospheric air extends up to many kilometres above the surface of the earth. The pressure exerted by the air is called atmospheric pressure.

39: If the area of your head is 15 cm × 15 cm, how much air (in weight) would you carry on your head?

Answer:  The weight of air column of the height of the atmosphere and area 15 cm × 15 cm is equal to the weight of an object of mass 225 kg (2250 N).  We have air inside our body, so we are not crushed under this weight and pressure of air is equal at both the sides.

Long Answer Type Questions

1: Explain contact and non-contact forces. Give two examples for each.

Answer:   Contact forces:  Forces which act only when there is physical contact between two interacting objects are known as Contact forces. Example: Muscular force: This is the force we can exert with our bodies by using our muscles, e.g: push, pull etc. Frictional force:  The force acting against the relative motion of surfaces in contact is called frictional force or friction.

Non-contact forces: Forces which can act without physical contact between objects, i.e. those that can act from a distance, are called non-contact forces or field forces. Example: Magnetic force: Magnets exert forces of attraction or repulsion on other magnets Electrostatic force: The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.

2: (a) How can friction be reduced? (b) How can it be increased? Give examples.

Answer:  We can reduce Friction

1. By using wheels and ball bearings. Use of wheels between surface moving over each other reduces friction. Ball bearings have small balls of steel between steel surfaces. Because of the balls the steel surfaces can easily moves over each other.

2. By making the rubbing surfaces smooth by polishing them.

3. By using a suitable lubricant, like oil (for light machinery) or grease (for heavy machinery). This helps because fluid friction is less than solid friction.

4. Friction due to air (air resistance) or water is reduced by using streamlined shapes in aeroplanes or ships. A streamlined shape is narrow in front and broader at the back. Birds and aquatic animals have streamlined shapes which held them in flying or swimming.

We can increase Friction by the following ways:

1. Sand and gravel is strewn on slippery ground during the rainy season to increase friction. It is then easier to walk on the ground.

2. By making the moving surfaces rough, e.g. tyres have designs and patterns with grooves on the surface to increase resistance with the road. This prevents slipping of the tyres on a wet road.

3. To increase friction, spikes are provided in the soles of shoes used by players and athletes.

3: Do liquid and gases exert pressure on the walls of container in all direction? Give example to justify your statement. 

Answer:  Liquid and gases exerts pressure on the walls of container. For example, If we take a plastic bottle and drill four holes around near the bottom of bottle at the same height. After filling the water in that bottle, we observe that water comes out of the holes and falls at the same distance. This shows that liquid exerts pressure on the walls of container in all directions. Similarly, we are not able to inflate a balloon which has holes because air inside balloon exerts pressure in all direction. Hence we can say that gases exert pressure on the walls of container in all directions.

4: Why is it easy to push a nail into a wooden plank by the pointed end? 

Answer:   It is easy to push a nail into a wooden plank by pointed end because the smaller the area, larger the pressure on a surface for the same force. The area of the pointed end of the nail is much smaller than that of its head. The same force therefore produces a pressure sufficient to push the pointed end of the nail into the wooden plank.

5: Read Table and try to identify the action as push or pull.

Answer:  Table Identifying Actions as Push or Pull

6: Read Table and complete it.

Answer:  Table Studying the Effect of Force on Objects

  7: What are the various effects of force on different objects?

Answer:  The various effects of force are: (i) A force can make an object move from rest. (ii) It can change the speed of a moving object. (iii) It can bring about a change in the shape of an object. (iv) It can change the direction of motion of an object. (v) It can cause some or all of these effects.

8: What are contact forces? State different types of contact forces.

Answer:  The forces which come into play only when two objects come in contact with each other are called contact forces. Some contact forces are: (i) Muscular force: The forces resulting due the action of muscles are known as muscular forces. Muscular force is a contact force because it comes into play when two object, come in contact with each other. (ii) Force of friction: When a body is moving, then a force equal and opposite to the direction of motion is exerted on that moving body. This force is called force of friction. It is also a contact force because it is exerted when two surfaces come in contact with each other.

9: What are non-contact forces? Explain different types of non-contact forces.

Answer:  The forces which can be exerted from a distance, without establishing a contact are called non-contact forces. Some non-contact forces are:

(i) Magnetic force:  The force exerted by a magnet on other magnet or some other magnetic substance like iron is called magnetic force. Like poles of a magnet repel each other and unlike poles of a magnet attract each other without contact. So it is called non-contact force.

(ii) Electrostatic force:  The force exerted by a charged body on other charged or uncharged body is called electrostatic force. Electrostatic force also acts without making a direct contact with other charged or uncharged body. So it is also a non-contact force.

(iii) Force of gravity : Earth pulls every thing or body towards it. The force of attraction exerted by earth on any object is called force of gravity. This is also a non-contact force as it acts from a distance.

10: What is force? Name different types of forces.

Answer:  A push or pull on an object is called force. There are following types of forces: (i) Muscular force (ii) Force of friction (iii) Magnetic force (iv) Force of gravity (v) Electrostatic force

11: Prove that the force of friction depends on the nature of the two surfaces in contact.

Answer:  Collect the following things: A thick book, nylon cloth, gunny cloth, plastic sheet, jute cloth and sand paper. Place the book on each of the materials and slide it on the floor one by one. If your book slides off the plastic sheet or nylon cloth, use adhesive tape to stick it firmly on the surface of the book.

You will observe that the different materials offer different amounts of resistances to sliding. This activity shows that force of friction depends on the nature of the surface in contact. In general, smooth surface offers lesser friction than rough surface.

12: Prove that the pressure exerted by water at the bottom of the container depends on the height of its column.

Answer:  Take a transparent glass tube or plastic pipe. Also take piece of thin sheet of a good quality rubber. Stretch the rubber sheet tightly over one end of pipe. Hold the pipe at the middle, keeping it in a vertical position. Pour some water in the pipe. Note the height of the water column in the pipe. Pour some more water. Observe, the bulge in rubber sheet and height of water column in the pipe. Repeat this process a few more times. You observe that as the height of water column increases the bulge in the rubber sheet also increases.

13: Show that a liquid exerts pressure on the walls of the container.

Answer:  Take a plastic bottle. Fix a cylindrical glass tube a few cm long near its bottom. You can do so by slightly heating one end of the glass tube and then quickly inserting it near the bottom of the bottle. Make sure that water does not leak from the joint. If there is any leakage seal it with molten wax. Cover the mouth of the glass tube with a thin rubber sheet. Now fill the bottle up to half with water. We observe the bulge in the rubber sheet. Pour some more water in the bottle. We see more bulge in rubber sheet. This activity indicates that water exerts pressure on the walls of the container.

14: Explain that liquids exert equal pressure at the same depth.

Answer:  Take an empty plastic bottle. Drill four holes all around near the bottom of the bottle. Make sure that all the holes are at the same height from the bottom. Now fill the bottle with water. We observe that different streams of water coming out of the holes fall at the same distance from the bottle. This observation indicates that liquids exert equal pressure at the same depth.

15: What experiment was performed to prove that air has pressure?

Answer: Otto von Guericke, a German Scientist invented a pump in 17th century to extract air out of a vessel. He demonstrated the force of the air pressure. He joined two hollow metallic hemispheres of 51 cm diameter each and pumped air out of them. Then he employed eight horses on each hemisphere to pull them apart. So great is the force of air pressure that the hemispheres could not be pulled apart.

Force and Pressure

Class 8 - ncert science solutions.

Give two examples each of situations in which you push or pull to change the state of motion of objects.

(a) Pull situations (in which state of motion of objects is changed) :

• Moving a book placed on a table towards ourself to read.
• We pull the clothes out of the washing machine after they are clean.

(b) Push situations (in which state of motion of objects is changed) :

• A football player taking a penalty kick, hits (or pushes) the ball towards the goal.
• A cricket ball hit by a batsman.

Give two examples of situations in which applied force causes a change in the shape of an object.

• When we press a lump of dough kept on a plate with our hands, its shape changes.
• When we press a smiley ball, its shape changes.

Fill in the blanks in the following statements.

(a) To draw water from a well, we have to ............... at the rope.

(b) A charged body ............... an uncharged body towards it.

(c) To move a loaded trolley, we have to ............... it.

(d) The north pole of a magnet ............... the north pole of another magnet.

(a) To draw water from a well, we have to pull at the rope.

(b) A charged body attracts an uncharged body towards it.

(c) To move a loaded trolley, we have to pull or push it.

(d) The north pole of a magnet repels the north pole of another magnet.

An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information, fill up the gaps in the following statements using the following terms.

muscular, contact, non-contact, gravity, friction, shape, attraction

(a) To stretch the bow, the archer applies a force that causes a change in its ...............

(b) The force applied by the archer to stretch the bow is an example of ............... force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a ............... force.

(d) While the arrow moves towards its target, the forces acting on it are due to ............... and that due to ............... of air

(a) To stretch the bow, the archer applies a force that causes a change in its shape .

(b) The force applied by the archer to stretch the bow is an example of muscular force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force.

(d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to friction of air.

In the following situations, identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

(b) Taking out paste from a toothpaste tube.

(c) A load suspended from a spring while its other end is on a hook fixed to a wall.

(d) An athlete making a high jump to clear the bar at a certain height.

A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

The muscular force applied by the blacksmith on the hot piece of iron changes the shape of the iron and hence, it can be moulded in any desired shape.

An inflated balloon was pressed against a wall after it had been rubbed with a piece of synthetic cloth. It was found that the balloon stuck to the wall. What force might be responsible for the attraction between the balloon and the wall?

An electrostatic charge develops on the balloon after it has been rubbed with a synthetic cloth. Due to this charge the balloon sticks to the wall. The electrostatic force is responsible for the attraction between the balloon and the wall.

Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

We use muscular force in order to hold the bucket of water above the ground. This muscular force acts against the force of gravity that pulls the bucket towards the ground. The two forces are equal in magnitude and opposite in direction. As a result, the net force on the bucket is zero. Hence, there is no change in the state of motion.

A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.

When a rocket has been fired upwards to launch a satellite in its orbit, two forces acting on it are:

• Force of gravity acting downwards
• Frictional force due to the earth's atmosphere, which opposes its motion.

Question 10

When we press the bulb of a dropper with its nozzle kept in water, the air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to

• pressure of water
• gravity of the earth
• shape of rubber bulb

atmospheric pressure

Reason — When all the air escapes from the nozzle, a low pressure develops inside the tube. Due to this the atmospheric pressure, acting on water becomes more than the pressure inside the tube. As water moves from a higher pressure area to a lower pressure area, hence on releasing the bulb, water gets filled in the dropper.

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8th Class Science Force and Pressure Question Bank

Done force and pressure total questions - 78.

question_answer 1) Force is a

A) push                 done clear

B) pull done clear

C) both (a) and (b) done clear

D) none of these done clear

question_answer 2) 1 newton = _______ dynes.

A) 103                   done clear

B) 104 done clear

C) 105                   done clear

D) 106 done clear

question_answer 3) The CGS unit of force is

A) newton            done clear

B)          pascal done clear

C) dyne                 done clear

D)          None of these done clear

question_answer 4) Which of the following is an example of contact force?

A) Magnetic force done clear

B)          Gravitational force done clear

C) Electric force    done clear

D) Muscular force done clear

question_answer 5) Force per unit area is _______.

A) thrust                 done clear

B)          pressure done clear

C) buoyancy                     done clear

D) density done clear

question_answer 6) As we go to the higher altitude the atmospheric pressure _______.

A) increases       done clear

B) remain same done clear

C) decreases                     done clear

D) cannot say done clear

question_answer 7) Pascal is equal to:

A) \[\text{N/}{{\text{m}}^{\text{2}}}\] done clear

B)                      \[\text{N/m}\times \text{s}\] done clear

C) \[\text{N/c}{{\text{m}}^{\text{2}}}\]                      done clear

D) \[\text{N}\text{.}{{\text{m}}^{\text{2}}}\] done clear

question_answer 8) Two stones A and B of masses 2 kg and 5 kg respectively are released from same height in vacuum. Which will reach on the ground first?

A) Stone A done clear

B) Stone B done clear

C) Both will reach at same time done clear

D) None of these done clear

question_answer 9) Pressure is directly proportional to

A) density done clear

B) height/depth done clear

C) acceleration due to gravity done clear

D) all of these done clear

question_answer 10) Electrostatic force is a

A) contact force done clear

B)          non-contact force done clear

C) balanced force done clear

D) unbalanced force done clear

question_answer 11) When a force of 10 N is applied on a body it starts moving with a constant acceleration of2 m/s2. The mass of the body is

A) 2kg                               done clear

B) 0.2kg done clear

C) 20kg                             done clear

D) 5kg done clear

question_answer 12) When a cricketer catches the ball by his hands the force/forces coming in action is/are

A) non-contact force         done clear

B) gravitational force done clear

C) frictional force  done clear

D) both (b) and (c) done clear

question_answer 13) A stone falling from the roof of a house due to

A) gravitational force done clear

B) magnetic force done clear

D) electrostatic force done clear

question_answer 14) Force has

A) only direction   done clear

B) only magnitude done clear

C) both magnitude and direction done clear

D) neither magnitude nor direction done clear

question_answer 15) The SI unit of force is

A) newton      done clear

B) dyne done clear

C) pascal             done clear

question_answer 16) Which instrument is used for measuring at mospheric pressure?

A) Hygrometer                  done clear

B) Barometer done clear

C) Hydrometer done clear

D) Sphygmomanometer done clear

question_answer 17) A fluid is a substance that

A) has no definite shape done clear

B) has no definite volume and shape done clear

C) has no definite volume done clear

D) is a liquid done clear

question_answer 18) A mass of 2 kg is accelerated at 2 m/sec2. Find the force applied on it.

A) 4N                               done clear

B) N done clear

C) 8N                               done clear

D) N done clear

question_answer 19) A stone of mass 4 kg is dropped from a height. Find the force exerted by it on ground if acceleration due to gravity is 10 m/s2.

A) 20 N                            done clear

B) 2.5 N done clear

C) 40 N                done clear

D) 0.4 N done clear

question_answer 20) How much pressure will be applied on a body. If a force of 4 N is applied on its unit surface area. [Hint: Area = 1 m2]

A) 0.25 Pa                        done clear

B) 2 Pa done clear

C) 8 Pa                             done clear

D) 4 Pa done clear

question_answer 21) A force of 12 N is acting perpendicular on a wooden block. What will be the thrust on it?

A) 12 N      done clear

B)          24 N done clear

C) 48 N                            done clear

D) 6N done clear

question_answer 22) Pressure is the ratio of force to the ____over which it is applied.

A) surface                         done clear

B) volume done clear

C) distance                       done clear

D) area done clear

A) \[A\to (q);B\to (p);C\to (r);D\to (s)\] done clear

B) \[A\to (r);B\to (p);C\to (q);D\to (s)\] done clear

C) \[A\to (p);B\to (r);C\to (s);D\to (q)\] done clear

D) \[A\to (s);B\to (q);C\to (p);D\to (r)\] done clear

D) \[A\to (s);B\to (r);C\to (q);D\to (p)\] done clear

B) \[A\to (r);B\to (s);C\to (q);D\to (p)\] done clear

question_answer 26) DIRECTIONS: Read the passage given below and answer the questions that follow. Passage Liquid pressure in a container doesn't depend on the shape of the container but it any depends on the height of the liquid column. The pressure due to a liquid at a point at a depth h from the surface of the liquid is given by\[P=\rho gh\]where, \[\rho \] is the density of the liquid and g is the acceleration due to gravity. A cylindrical container is full of water. The pressure at the bottom is P. Now, the water is replaced by cooking oil of density twice the density of water. The new pressure at the bottom is

A) 4 P                   done clear

B) 2 P done clear

C) 1.5 P done clear

D) 3P done clear

question_answer 27) DIRECTIONS: Read the passage given below and answer the questions that follow. Passage Liquid pressure in a container doesn't depend on the shape of the container but it any depends on the height of the liquid column. The pressure due to a liquid at a point at a depth h from the surface of the liquid is given by\[P=\rho gh\]where, \[\rho \] is the density of the liquid and g is the acceleration due to gravity. A cylindrical container is full of water. The pressure at the bottom is P. Now, the water is replaced by cooking oil of density twice the density of water. If half of the water is taken out, what is the pressure at the bottom?

A) P                      done clear

B) \[\frac{1}{2}P\] done clear

C) \[\frac{3}{2}P\]                      done clear

D) 2P done clear

question_answer 28) DIRECTIONS: Read the passage given below and answer the questions that follow. Passage Liquid pressure in a container doesn't depend on the shape of the container but it any depends on the height of the liquid column. The pressure due to a liquid at a point at a depth h from the surface of the liquid is given by\[P=\rho gh\]where, \[\rho \] is the density of the liquid and g is the acceleration due to gravity. A cylindrical container is full of water. The pressure at the bottom is P. Now, the water is replaced by cooking oil of density twice the density of water. If the container is carried on a mountain then what will be the pressure at the bottom?

A) less than P       done clear

B) more than P done clear

C) equal to P         done clear

question_answer 29) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: Steel nails are pointed at one end to have least area of contact with surface. Reason: Least area exerts high pressure.

A) Both A and R are true and R is the correct explanation of A. done clear

B) Both A and R are true but R is not the correct explanation of A. done clear

C) A is true but R is false. done clear

D) A is false but R is true. done clear

question_answer 30) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: Magnetic force is a non-contact force. Reason: Unlike poles of magnet attracts each other.

question_answer 31) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: A moving toy car stops after a little distance. Reason: Friction opposes the motion.

question_answer 32) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: Apple falls on the ground, due to gravitational force. Reason: Gravitational force is a contact force.

question_answer 33) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: Sea divers wear special suits. Reason: There is no effect of gravity under the sea.

question_answer 34) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: Fluid exerts pressure on the walls of container. Reason: Fluids have definite shape and size.

question_answer 35) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: There is high atmospheric pressure in the space. Reason: Astronauts wear special suits.

question_answer 36) Direction: The questions in this segment consist of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: When a stone is thrown vertically upward, after getting a certain height' it comes back to the earth. Reason: Stone has to work against the force of friction of air.

question_answer 37) DIRECTIONS: Read the following two statements carefully and choose the correct options. Statement-1: When one body moves or tries to move on the surface of another body, its speed continuously decreases. Statement-2: Friction is a contact force.

A) Statement (1) is correct while statement (2) is incorrect. done clear

B) Statement (2) is correct while statement (1) is incorrect. done clear

C) Both statements are correct done clear

D) Both statements are incorrect. done clear

question_answer 38) DIRECTIONS: Read the following two statements carefully and choose the correct options. Statement-1: Atmospheric pressure increases with increase in depth of sea. Statement-2: Pressure is directly proportional to depth/height.

A) move in the direction of force A done clear

B) move in the direction of force B done clear

C) not move          done clear

A) point A            done clear

B)          point B done clear

C) point C                        done clear

D) point D done clear

A) Same in A and B         done clear

B) Container B done clear

C) Container A      done clear

D)         None of these done clear

A) 160 Pa done clear

B)          80 Pa done clear

C) 40 Pa   done clear

D) 240 Pa done clear

question_answer 43) Opening a door is an example of

C) magnetic force done clear

D) balanced force done clear

question_answer 44) When a body is said to be under balanced forces then the resultant force applied on the body is

A) one                  done clear

B)          infinite done clear

C) zero     done clear

D)          none of these done clear

question_answer 45) Two bodies of masses m and 6m are moving under same magnitude of force. The ratio of their accelerations will be

A) 1 : 6                 done clear

B)          6 : 1 done clear

C) 1 : 36               done clear

D)          36 : 1 done clear

question_answer 46) The pressure of the water at the bottom of the pond is _______ at the surface of the pond.

A) lower than        done clear

B)          same done clear

C) higher than done clear

D) either lower or higher done clear

question_answer 47) If a pressure of 8 Pa acts on the surface of area2m2, then the force acting on the surface is

A) 10 dynes           done clear

B)          4.00 N done clear

C) 16N           done clear

D) 4.00 dynes done clear

question_answer 48) The pressure exerted by a column of liquid is independent of the ______.

A) density of the liquid done clear

B) weight of the liquid done clear

C) depth of the liquid done clear

D) shape of the container done clear

question_answer 49) A force \[{{F}_{1}}\] acting on a body of 2 kg produces an acceleration of 2.5 m/sec2. Another force \[{{F}_{2}}\]acting on the body of mass 5 kg produces an acceleration of 2 m/sec2. Find the ratio of\[{{F}_{2}}/{{F}_{1}}.\]

A) 2                      done clear

B)          4 done clear

C) 6                                  done clear

D) 8 done clear

question_answer 50) An astronaut with all her equipment has a mass of 95 kilograms. How much will the weight on the moon, where the acceleration due to gravity is \[1.67\,\text{m}{{\text{s}}^{-2}}?\]

A) 159 N  done clear

B)          169 N done clear

C) 149 N             done clear

D) 100 N done clear

question_answer 51) What force is needed to a accelerate a 60 kg wagon from rest to \[5.0\,\text{m}{{\text{s}}^{-2}}\] in 2.0 seconds?

A) 100 N             done clear

B) 120 N done clear

C) 150 N          done clear

D) 130 N done clear

question_answer 52) A 500 kg rocket is fired straight up from the earth, the engine providing 7500 newton of thrust. Its acceleration is

A) 4.5 m/s2           done clear

B) 5.2 m/s2 done clear

C) 9.8 m/s2           done clear

D) 15 m/s2 done clear

question_answer 53) When a body is stationary

A) there is no force acting on it done clear

B) the force acting on it not in contact with it done clear

C) the combination of forces acting on it balances each other done clear

D) the body is in vacuum done clear

question_answer 54) What force would be required to produce an acceleration of 4 m/s2 in a moving wall of mass6kg?

A) 1.2 N               done clear

B) 1.5 N done clear

C) 24 dynes           done clear

D)          24 N done clear

question_answer 55) Two forces 200 N and 300 N acting on a body in same direction. What is resultant force?

A) 1.5 N               done clear

B)          100 N done clear

C) 0.66 N            done clear

D) 500 N done clear

question_answer 56) What will be the change in acceleration of as liding brick, if its mass is doubled, while a constant force is acting on it. Acceleration will be

A) 2a                    done clear

B)          a/2 done clear

C) a/4                               done clear

D) 4a done clear

question_answer 57) A car of mass 1000 kg can produce an acceleration of 8 m/s2.Calculate the force produced by the engine ignoring friction.

A) 10,000 N          done clear

B)          100,000 N done clear

C) 8000 N           done clear

D) 18000N done clear

question_answer 58) When an object is at rest on a surface - what canbe said about the forces on it?

A) they all are equal done clear

B) they are unbalanced done clear

C) there are not acting on it done clear

D) all the forces cancel out done clear

question_answer 59) What is the surface area of table top if a force of120 N exerted on it produces a pressure of20 Pa?

A) 2400m2            done clear

B) 60m2 done clear

C) 6m2                  done clear

D) 240m2 done clear

question_answer 60) The pressure at a point in a liquid is proportional to the________ of the liquid and the depth of the point.

B)          force done clear

C) area done clear

D) gravitational acceleration done clear

question_answer 61) Gaurav wants to accelerate a body of mass2 kg at 10 m/sec2. On the other hand, Sahil wants to get accelerate a body of mass 5 kg at 2.5m/sec2. Who will need to apply more force?

A) both will apply same force done clear

B) Gaurav done clear

C) Sahil done clear

question_answer 62) Stones A, B, C and D of same masses are thrown on a wall. Acceleration produced in them are \[2m/se{{c}^{2}},\text{ }3\text{ }m/se{{c}^{2}},\text{ }5\text{ }m/se{{c}^{2}},\text{ }4\text{ }m/se{{c}^{2}}\] respectively. Arrange the force exerted by the stones in descending order.

A) \[{{f}_{A}}>{{f}_{B}}>{{f}_{C}}>{{f}_{D}}\] done clear

B)          \[{{f}_{D}}>{{f}_{C}}>{{f}_{B}}>{{f}_{A}}\] done clear

C) \[{{f}_{A}}>{{f}_{B}}>{{f}_{D}}>{{f}_{C}}\]           done clear

D) \[{{f}_{C}}>{{f}_{D}}>{{f}_{B}}>{{f}_{A}}\] done clear

D) \[A\to (s);B\to (p);C\to (q);D\to (r)\] done clear

C) \[A\to (q);B\to (r);C\to (s);D\to (p)\] done clear

A) Book 1             done clear

B) Book 2 done clear

C) Both exert equal pressure done clear

D) Can't be determined done clear

A) 5N/m2  done clear

B)          100 N/m2 done clear

C) 200 N/m2         done clear

question_answer 67) Directions: The questions in this segment consists of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: The acceleration produced by a force in the motion of a body depends only up on its mass. Reason: Larger is the mass of the body, lesser will be the acceleration produced.

B) Both A and R are true and but R is not the correct explanation of A. done clear

C) A is true but R is a false. done clear

question_answer 68) Directions: The questions in this segment consists of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: If the net external force on the body is zero, then its acceleration is zero. Reason: Acceleration does not depend on force.

question_answer 69) Directions: The questions in this segment consists of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: An object can move with constant velocity if no net force acts on it. Reason: No net force is needed to move an object with constant velocity.

question_answer 70) Directions: The questions in this segment consists of two statements, one labelled as ?Assertion A? and the other labelled as ?Reason R?. You are to examine these two statements carefully and decide if the Assertion A and Reasons R are individually true and if so, whether the reason is a correct explanation of the assertion. Select your answers to these items using codes given below. Assertion: A body is momentarily at rest when it reverses the direction. Reason: A body cannot have acceleration if its velocity is zero at a given instant of time.

question_answer 71) DIRECTIONS: Read the following three statements carefully and choose the correct option. Statement-1: It is easier to push a nail into a wooden box by the pointed end. Statement-2: Nail's head is easier to hit. Statement-3: Pressure applied on all nails is same whatever is their size.

A) Statement (1) and (3) are incorrect while statement (2) is correct. done clear

B) Statement (1) and (2) are incorrect while (3) is correct. done clear

C) All the statements are correct. done clear

D) All the statements are incorrect. done clear

question_answer 72) DIRECTIONS: Read the following three statements carefully and choose the correct option. Statement-1: Porters place a round piece of cloth on their heads. Statement-2: Pressure is inversely proportional to area on which it acts. Statement-3: Pressure is independent of area of surface in contact.

A) A                                  done clear

B) B done clear

C) Both A and B               done clear

A) 5kg                   done clear

B) 70kg done clear

C) 2.5kg                            done clear

D) 17.5kg done clear

A) 10 N                done clear

B)          20 N done clear

C) N                     done clear

A) Pa                    done clear

B)          0.2 Pa done clear

C) 20 Pa               done clear

D) 200 Pa done clear

A) east             done clear

B)          west done clear

C) north             done clear

D)          south done clear

A) spring scale      done clear

B) voltmeter done clear

C) thermometer    done clear

D) graduated cylinder done clear

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Force and Pressure Class 8 Notes, Question Answers, Explanation

by admin | Jan 31, 2019 | CBSE Class 8 Science Lessons Explanation, Notes, NCERT Question Answers | 0 comments

Force and Pressure Class 8 Science Chapter 11 as per NCERT Book used in CBSE and other Schools. The lesson covers the complete explanation of class 8 Chapter 11 Force and Pressure. Topics covered are force and types of force, fluids and fluids pressure. The lesson covers all important questions based on force and pressure. NCERT solutions to book questions have also been provided for convenience of the students.

Force plays a great role in our life as it is helpful in doing any work. Like in playing cricket and basketball. We need force to play. Force is defined as a push or a pull or we can say force is a physical quantity that can change the speed, state, direction and dimension of an object. For example, when we put the force on the door it opens.

Force and Pressure Class 8 Video Explanation

The changes that force can bring are written as follows:

If someone pushes your bicycle, it starts moving faster. In this case, the force that we apply on the bicycle changes the speed of the bicycle. Speed can be increased or decreased also.

Note: Force comes into play when at least two bodies interact. Or we can say that two bodies are necessary to put force comes into play.

In this case, the body which is at rest can be put into motion or the body in motion goes in rest. For example: If a football placed on the ground is at rest, when you kick the football, it moves (comes in motion). We can also say that it changes the state of the body.

Dimension means shape and size. When you blow a metal rod with a hammer, the dimension changes.

For example: For brushing the teeth, we need to squeeze the toothpaste and apply it on our brush. This leads to a change in the shape of the toothpaste.

Force also leads to a change in direction. While playing cricket, the one who throws the ball, throws it in straight position with respect to the one who is doing batting. But the one who is batting hits the cricket ball in different direction.

Another example is that while we drive the car, we push the force on staring due to which car moves or changes the direction.

Types of Forces

There are two types of forces which are as follows:

Contact Force

• Non-contact force

Examples of contact Force:

Muscular Force

Frictional force.

• Mechanical Force

Let us discuss them one by one-

Muscular force is the force that is caused by action of muscles inside the body. It is also a contact force. Like we cannot push or pull the book kept on a table without touching it. Or bucket filled with water cannot hold without touch. For this, we need to apply force that will be exerted with hands. This means our muscles play a role.

Animals make use muscular force to carry out physical tasks. Animals like bullocks, horses, donkeys etc need muscular force for different tasks.

Coolies use muscular force to lift luggage.

Athletes use this muscular force for running.

It is the force that opposes the motion of one body over the surface of another body. It is a contact force. We can say that in this force, one body tries to move on the surface of another body.

For example, writing anything with pen, book lying on the table, and walking on floor.

Mechanical force

It is the force exerted by any kind of machine and obviously it needs contact of another body due to which it is also called a contact force. For example: Turbines in Hydel power station.

Non-Contact Force

It is the force that acts when bodies are not physically in contact with each other. For example: Falling of apple from trees.

Apples always fall down without being in contact with tree and it is due to the gravitational force of earth.

Examples of Non-Contact Force:

Magnetic force

Electrostatic force, gravitational force.

It is the force exerted by magnets on iron objects.

The force between magnet and iron is attractive type of force, which means it always attract toward each other and never repel each other. It is used in extracting scrap iron from garbage.

It is the force of attraction or repulsion exerted between charged particles.

It can be either between same charges (repulsive, this means they repel each other) or between opposite charges (attractive, this means that they both attract each other).

It is the force exerted by earth’s gravity on all objects. It is always attractive in nature.

For example: Falling of apple from tree or falling of any object when we through anything up.

Question: Give two examples of each of situations in which you push or pull to change the state of motion of objects?

a. When we push a bicycle to move it.

b. When we pull the table it leads to change in position of table.

Question: Give two examples of situation in which applied force causes a change in the shape of an object?

Answer: When we press the foam, its shape is changed.

The shape of rubber band changes while we stretch the rubber band.

Question: A blacksmith hammers a hot piece of iron while making a tool, How does the force due to hammering affect the piece of iron?

Answer: The force due to hammering cause the change in shape of iron and iron can be molded in the shape of the required tool.

Question: Name the forces acting on a plastic bucket containing water held above ground level in our hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion?

Answer: The forces exert on the bucket are muscular and gravitational force. The force acting on the bucket do not bring a change in state of motion because they are acting in opposite directions with equal magnitudes. Therefore, the net force acting on bucket remains zero.

So we can say that pressure is the force exerted per unit area. Another example for this is that when we add hot water into a plastic bottle it melts due to pressure (atmospheric pressure).

Factors on which pressure depends are as follows:

• It is directly proportional to force. This means if pressure increases automatically force increases. Alternatively, if pressure decreases force also decreases.
• It is inversely proportional to area. This means that if pressure increases area decreases. But if pressure decreases area increases. We can say that they both are opposite to each other.

Formula: Pressure = Force/Area

Unit of pressure

S.I (system Internationale) Unit of pressure (System international unit) : PASCAL

1 PA= 1 NEWTON/1 METER SQUARE

Pressure is defined as 1 pascal when 1 Newton (it is SI unit of force) force is applied on 1-meter square (SI unit of area) area.

Let us discuss few facts of daily life which are based on Pressure:

School bags have wide and thin straps, but we select the bag with a wide strap. Wide strapped bags are used because they are easy to handle.

We know that pressure is inversely proportional to area, therefore, the larger the area the lesser the pressure exerted therefore it becomes easy to carry a school bag with a wide strap.

As we know that pressure is inversely proportional to area, therefore, the more the area the lesser the pressure exerted. Therefore high pressure exerted by dams can be born on ground and that avoids breakage of the dam. That is the reason why dams are always constructed with a wide base.

As we know that pressure is inversely proportional to area, therefore, the lesser the area the more the pressure exerted therefore it becomes easy to hammer that nail. That is the reason sharp nails are preferred over blunt nails.

It is difficult to walk on sandy floor with pencil heels

It is easy to peel vegetables with sharp knife instead of using blunt knife. This is because and also we know that pressure is inversely proportional to area therefore less is the area more is the pressure exerted.

Fluids are those that can flow. For example: Liquids including water and gases including air. As we know that there are three sources of matter solid, liquid, and gas. In solid, particles are tightly packed and it is very difficult for those particles to flow. In liquid, the particles are loosely packed and it can flow easily. In gases, particles are extremely loosely packed and can also flow easily.

Fluid Pressure

It is defined as the pressure exerted by fluids.

Properties of Fluid Pressure

There are different properties of fluid pressure which are as follows:

• Pressure increases with an increase in depth. Like if we take a container filled with water. Suppose A is placed at the bottom and B is placed at the top of container. As per this property, the point A has high pressure.
• Pressure decreases with height. Like the one person who stands on plane experiences high pressure with respect to the one who stands on the top of a hill. Thus we can say that pressure decreases with depth.
• Pressure applied at any point is equally transmitted in all directions. Like we see water coming out from leaking pipes and taps flows in all directions. In case of a bath shower and fountain, water comes out tiny holes and flows in all directions.

While climbing the hills, the pressure decreases with height. That is why we always carry oxygen cylinder with us while climbing. This cylinder is helpful in proper respiration.

Pressure applied at any point is equally transmitted in all directions

Like a flask which is filled with water. This flask has multiple holes. When we push the piston (placed at the top of flask), by doing this we are giving force per unit area (pressure). Due to this pressure applied, water flows equally in all direction.

Let us take an example. Suppose there is a flask filled with water. Also suppose, there is a point A which is at the bottom of the flask and another point B which is placed at the top of the flask. The point A experiences high pressure with respect to point B.

Q. Why a camel can easily walk on sand?

Answer: This is due to the fact that nature has provided the camel with broad feet. Hence, when a camel walks on sand, the pressure exerted by it on the sand is quite small due to the increased area of contact, its feet do not sink much in the sand. Therefore, a camel can easily cross vast regions in deserts.

Q. Why do some people suffer from nose bleeding at high altitudes?

Answer: The atmospheric pressure is at a maximum on the surface of the earth. When we go to a higher altitude (say a high mountain), then the atmospheric pressure decreases. So, at high altitudes, the atmospheric pressure becomes much less than our blood pressure. Since our blood is at a higher pressure than the outside pressure, therefore, some of the blood vessels in our body burst and nose bleeding can occur at high altitudes.

Question: Why do climbers take oxygen cylinder along while climbing height?

Answer: Atmospheric Pressure decreases with height, therefore, oxygen available for breathing is comparatively less. As a result, nausea kind of disorder is commonly seen and sometimes the blood vessels get burst and mountaineers bleed through the nose (due to increased pressure). This is the reason that mountaineers carry oxygen cylinders with them.

Q. Why do astronauts wear special suits in space?

Answer: Spacesuits help astronauts in several ways. Spacewalking astronauts face a wide variety of temperatures. In the Earth’s orbit, conditions can be as cold as minus 250 degrees Fahrenheit. In the sunlight, they can be as hot as 250 degrees. A space suit protects astronauts from those extreme temperatures.

Spacesuits also supply astronauts with oxygen to breathe while they are in the vacuum of space. They contain water to drink during spacewalks. They protect astronauts from being injured from impacts of small bits of space dust.

Question: Why do deep sea divers wear special suits while diving?

Answer: Liquid pressure increases with depth: Pressure is high at the bottom therefore deep sea divers have to wear special suits to protect themselves from high pressure otherwise it may crush their bodies.

Q. Why an apple always falls to the ground from the tree?

Answer: The earth pulls the apples down due to the force of gravity or gravitational force.

Q. Why is a heavy truck fitted with six to eight wheels?

Answer: A heavy truck is fitted with six to eight wheels because increased area reduces the pressure on wheels so they do not burst or damage on the road. That is why truck has broad tyres so that there is less pressure on the ground and the tyres do not sink in the soil.

Q. Why do skiers use long flat skies to slide over snow?

Answer: Skiers use long and flat skies to slide on the snow. A large area of the cross-section of skies reduces the pressure on the snow and prevents the skiers from sinking into the soft ground. So, the skiers easily slide over snow without sinking their feet into the ground.

Time to check knowledge by answering the following questions-

Fill in the blanks :

• _________ is a push or pull acting on an object.
• Magnetic and gravitational forces are the types of _______ force.
• The S.I. unit of pressure is_______
• It is easier to carry school bags with ________straps.
• Foundations of high-rise buildings are kept________
• Iron nails can be separated from husk by using_________
• non – contact
• wide foundation

State whether True or False: 

• The pressure in a liquid at greater depths is greater. 
• A piece of rubber regains its shape on squeezing. 
• Cutting and piercing tools have blunt edges. 
• Camel cannot walk on sand due to its broad feet. 
• Non-contact force can act from a distance. 
• The syringe works on a principle of atmospheric pressure. 
• People at plains suffer from nose bleeding. 
• Fluids exert pressure. 

Let’s do some Activities:

Activity to show that pressure increases with depth

• Firstly,  we need to take a plastic container.
• Then we need to make 3 holes at different heights.
• Put the container under a tap.
• Then we need to observe the force with which water flows out through all holes
• It is observed that water flows with great pressure from last hole as compare to the other holes.
• This shows that pressure increases with depth.

Question: How can gas pressure be measured?

Answer: Gas pressure can be measured by using an instrument called  Manometer. It consists of u-shaped glass tube which contains mercury. The level of mercury is initially same in both arms to measure gas pressure. Then to measure gas pressure, we need to connect one side of the manometer with gas supply. By doing so, we can observe the pressure of gas.

Working of Manometer

The gas present in the manometer exert pressure therefore mercury level moves down in one limb and rises in other limb. The difference in the level of mercury in both arms determines gas pressure.

We know that air is all around us. The atmosphere envelope of air around us called as atmosphere. It extends up to many kilometers.

There are five different layers present in the atmosphere.

Exosphere (topmost)

Thermosphere

Stratosphere

Troposphere (bottom)

Atmospheric Pressure

It is the pressure exerted by the atmospheric air.

Question: Why does a rubber sucker stick to the wall when it is pressed against the wall?

Answer: When we press the rubber sucker most of the air between surface and rubber escapes out and sucker sticks to wall due to atmosphere pressure acting on it. To pull it back, one needs to apply certain force which should be enough to overcome atmospheric pressure.

Atmospheric pressure can be measured by instrument barometer:

It consists of a trough which contains mercury with inverted tube. As atmosphere exerts pressure the mercury level from trough moves up which gives the value of atmospheric pressure that is 760mm on mercury scale.

NCERT Book Solutions

MULTIPLE CHOICE QUESTIONS (MCQS)

• Opening the door is an example of which type of force?
• (a) contact force
• (b) spring force
• (c) non-contact force
• (d) magnetic force

Answer: (a) contact force

• What is the cause of change in motion or change in the state of motion?
• (a) Pressure
• (b) Friction
• (c) Atmospheric Pressure

Answer: (d) Force

• A charged balloon attaches to a wall because of which force?
• (a) muscular force
• (b) magnetic force
• (c) electrostatic force
• (d) gravitational force

Answer: (c) electrostatic force

• A ball rolling on the ground slows down and finally stops. This is because of:-
• (b) less force applied
• (c) friction
• (d) none of the above

Answer: (c) friction

• In a tug-of-war, two teams pulling a rope does not move towards any team, it implies that:-
• (a) An equal force is being applied in the same direction
• (b) An equal force is being applied in opposite direction
• (c) no force is applied in any directions
• (d) cannot be explained

Answer: (b) An equal force is being applied in opposite direction

• Gravity is a which type of force?
• (a) repulsive force
• (b) attractive or Repulsive force
• (c) attractive force
• (d) not a force

Answer: (c) attractive force

• A push or pull on an object is called as?
• (a) pressure
• (b) Push-pull
• (d) all of above

Answer:  (c) force

• The pressure of the water at the bottom of the pond is at the surface of the pond?
• (a) lower than
• (c) higher than
• (d) either lower or higher

Answer: (c) higher than

• The force involved in falling of an apple from a tree is known as?
• (a) magnetic force
• (b) electrostatic force
• (c) contact force

Answer: (d) gravitational force

• Which of the following is an example of a non-contact force?
• (a) The force exerted by us to lift a bucket
• (b) push a stationary car
• (c) The force exerted by magnets
• (d) hit a cricket ball for a 6 run

Answer: (d) hit a cricket ball for a 6 run

• Pressure is defined as?
• (a) Area/Force on which it acts
• (b) Force/Area on which it acts
• (c) Volume/Force on which it acts
• (d) Force/Volume on which it acts

Answer: (b) Force/Area on which it acts

Question: When a comb rubbed against hair and is brought near the small pieces of paper?

Answer: When a comb or a plastic ballpoint pen is rubbed on dry hair, an electric charge is produced on it. This electric charge exerts a pull on the bits of paper. Thus the force exerted by an electrostatic charge is called an Electrostatic Force.

Question: Why do bodies not get crushed due to intense atmosphere pressure?

Answer: It due to pressure inside our bodies which is just equal to atmospheric pressure.

Question: Activity to show liquid exerts pressure at the bottom of container?

• Firstly, we need to take a tube of approximately length of 15cm.
• Take a piece of good quality rubber balloon.
• Stretch the rubber balloon over the end of tube.
• Then we need to hold the pipe in middle at vertical position.
• Now pour the water into it.
• You will notice balloon starts bulging.
• As more and more water is poured balloon bulges more.

Question: Activity to show liquid exerts pressure on walls of container also on the side of container.

For this activity

• We need to take a plastic bottle.
• Then fix cylindrical glass tube near to the bottom.
• Stretch rubber balloon on the mouth of tube.
• Now fill half of the bottle with water.
• Then, balloon starts bulging.
• It shows pressure is exerted on the walls of the container.

Question: Activity to show liquid exerts pressure at same depth?

• For this activity initially we need to take empty plastic bottle.
• Drill four holes near the bottom at same height.
• Now fill the bottle with water.
• Observe the streams of water coming out.
• Then we will see water flows with same pressure.
• This indicates that liquid exert equal pressure at same depth.

Question: Explain which type of force following are experiences:

• A horse pulling a cart — 
• A sticker attached to steel almirah without glue—
• A coin falling to the ground—–
• A plastic comb rubbed in dry hair picking up tiny pieces of paper——– 
• contact force
• magnetic force
• gravitational force
• electrostatic force

Question: Why does a sharp knife cut objects more effectively than a blunt knife?

A sharp knife has a very thin edge of its blade. A sharp knife cuts objects (like fruits, vegetables) better because due to its very thin edge, the force of our hand falls over a very small area of the object.

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Force and Pressure Class 8 Extra Questions and Answers Science Chapter 11

September 5, 2020 by Prasanna

In this page, we are providing Force and Pressure Class 8 Extra Questions and Answers Science Chapter 11 pdf download. NCERT Extra Questions for Class 8 Science Chapter 11 Force and Pressure with Answers will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 11 Extra Questions and Answers Force and Pressure

Extra Questions for Class 8 Science Chapter 11 Force and Pressure with Answers Solutions

Force and Pressure Class 8 Extra Questions Very Short Answer Type

Question 1. What is the name of the instrument used to measure atmospheric pressure? Answer: Barometer

Question 2. Give two examples of contact force. Answer:

• Muscular force
• Force of friction

Question 3. Name the force exerted on a ball of dough to make a flat chapati. Answer: Muscular force

Question 4. What kind of force is an electrostatic force? Answer: Non-contact force

Question 5. Is the gravity a property of earth only? Answer: No

Question 6. Name the force due to which every object falls on earth. Answer: Gravitational force

Question 7. What do you mean by pressure? Answer: Force per unit area (Force/Area)

Question 8. Do liquids and gases also exert pressure? Answer: Yes

Question 9. What are the two states of motion? Answer:

• The state of rest.
• The state of motion.

Question 10. What kind of force is friction? Answer: Contact force

Question 11. What type of force is gravitational force? Answer: Non-contact force

Question 12. Is it true that force acting on an object can also change its shape? Answer: Yes, it is true.

Question 13. While sieving grains, small pieces fall down. Which force pulls them down? Answer: Gravitational force

Question 14. How can we change the speed and the direction of a moving body? Answer: By applying force.

Question 15. What is the distance moved by an object in unit time called? Answer: Speed

Question 16. Does force of gravity act on dust particles? Answer: Yes

Question 17. Does the force of gravitation exist between two astronauts in space? Answer: Yes

Question 18. What is a force? Answer: A push or pull on an object is called force.

Question 19. What is the SI unit of pressure? Answer: Pascal (Pa)

Question 20. At least how many objects are needed to apply a force? Answer: At least two objects are needed to apply a force.

Question 21. Give one example of gravitational force. Answer: An apple falling from the tree to ground.

Question 22. What is meant by atmospheric pressure? Answer: The weight of air acting per unit area is known as atmospheric pressure.

Question 23. What do you mean by magnitude? Answer: The strength of a force is usually expressed by its magnitude.

Question 24. What is muscular force? Answer: The force resulting due to the action of muscles is known as muscular force.

Question 25. What is contact force? Answer: Force that can be applied only when it is in contact with an object is called contact force.

Question 26. What do you mean by the term atmosphere? Answer: The envelope of air all around us is known as atmosphere.

Force and Pressure Class 8 Extra Questions Short Answer Type

Question 1. Define pressure. Answer: The force acting per unit surface area is called pressure. SI unit of pressure is measured in Newton/ Metre2, which is equal to 1 Pascal (Pa).

Question 2. How do fluids exert pressure? Answer: Fluids exert pressure in all directions. Fluids also exert pressure on the walls of the container that hold them.

Question 3. A force of 100 N is applied on an area of 4 m 2 . Compute pressure being applied on the area. Answer: Given: Force = 100 N, Area = 4 m 2

Question 4. Which force is responsible for downward movement of a parachutes? Will he come down with the same speed without the parachute? Answer: Force of gravity is responsible for this downward movement. No, without parachute he will come down with a higher speed.

Question 5. Two thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain. Answer: Electrostatic force is responsible for this phenomenon. The two balls have similar charges, that’s why they move away due to repulsion between them.

Question 6. How does an applied force changes the speed of an object? Answer: If the applied force is in the direction of motion, the speed of the object increases. But if the force applied in the direction opposite to the motion, then it decreases the speed of the object.

Question 7. Name the forces acting on the car sticking to an electromagnet in a Junkyard. Which one of them is larger? Answer: Magnetic force (in the upward direction) and force of gravity or the weight of the car (downward). Magnetic force is larger than the force of gravity.

Question 8. What is the similarity between electrostatic and magnetic forces? Answer:

• Both are non-contact forces.
• Both are attractive as well as repulsive forces.

Question 9. What are the effects of force on an object? Answer:

• Force can change the state of motion of an object.
• Force changes the speed of a moving object.
• Force can cause an object to turn or change direction.
• Force can change the shape of an object.

Force and Pressure Class 8 Extra Questions Long Answer Type

Question 1. What is force? State the difference between contact force and non-contact force. A push or pull on an object is called a force. Answer:

Question 2. Define the different types of forces. Answer: Force can act on a body from a distance or by being in contact with it. Depending on this, forces can be classified as contact and non-contact forces. (a) Contact forces: When force is applied on an object by direct or indirect physical contact the applied force is called contact force. Muscular and frictional force are example of contact force.

• Muscular force: The force resulting due to the action of muscles is known as the muscular force.
• Frictional force: The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

(b) Non-contact forces: When a force is applied to an object by another body that is not in direct contact with it is called non-contact force. Gravitational, magnetic and electrostatic force are example of non-contact force.

• Gravitational force: The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity.
• Electrostatic force: The force exerted by a charged body on another charged or uncharged 1 body is known as electrostatic force.
• Magnetic force: The force exerted between a magnet and other magnet or magnetic material is known as magnetic force.

Question 3. Why it is easier to walk on soft sand if we have flat shoes rather than shoes with sharp heels (or pencil heels)? Answer: A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this the ‘flat’ shoes do not sink much in soft sand and it is easy to walk on it. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts a greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on it.

Question 4. What is pressure? What is the relation of pressure with area on which it is applied? Answer: Force exerted on per unit area is called pressure. Pressure is related with area on which it is applied. When the area is increased the pressure exerted is less. But when the area on which pressure is exerted is decrease the pressure increases. So we can conclude that pressure increases with decrease in area. List the characteristics of pressure exerted by a liquid.

• Liquid exerts pressure in all directions.
• Pressure in liquid does not depends on shape, size and surface area of the container.
• Pressure increases with depth.
• All points at the same level in a liquid are at the same pressure.
• Pressure does not depend on the surface of the immersed object.

Force and Pressure Class 8 Extra Questions HOTS

Question 1. We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect why? Answer: The pressure of air inside our body is same as that of the atmosphere. Therefore, we do not experience its effect

Question 2. Why do sea divers wear specially designed suits? Answer: Since the pressure of liquid increases with the increasing depth of sea. Specially designed suits protect scuba divers from the huge pressure of the water underneath.Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction.

Question 3. What do you infer about the magnitudes and direction of the forces applied? Answer: Both the persons are applying forces from opposite direction with equal magnitudes.

Question 4. An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down. Answer: The initial force is muscular force which sets the arrow in motion. The force of gravity that acts on the arrow in the downward direction brings it to the ground.

Question 5. Two rods: A and B, having same weight and equal length have different thickness. Rod A is thinner while Rod B is thicker. They are held vertically on the surface of sand. Which one of them will sink more? Why? Answer: Rod A will go deeper as it has a smaller area of contact, therefore the same force produces more pres¬sure. In case of rod B the same force produces less pressure.

Question 6. It is difficult to cut cloth using a pair of scissors with blunt blades. Explain. Answer: Blunt blades have larger area compared to the sharp-edged blades. Thus, the applied force produces a lower pressure in case of blunt blades, which makes it difficult to cut the cloth.

Force and Pressure Class 8 Extra Questions Value Based (VBQs)

Question 1. On Lokesh’s birthday Shreya was given charge to amuse children with some little tricks. Shreya sticked balloons to the wall by just rubbing them in her clothes. She bent the water stream from a tap without touching it. She did so by bringing big balloon near to the flowing water. All children were very happy on seeing this little magic. Everybody praised Shreya.

(a) How do balloons stick to walls? (b) How Shreya bent the water stream by bringing a big balloon near it and without touching it? (c) What values of Shreya is shown here? Answer: (a) On rubbing the balloon with hair or clothes, it acquire negative charges. The negative charges are attracted to the positive charges on the wall and balloon sticks to the wall. (b) Negative charge on the balloon attracts positive charge on water molecules. Thus, bent the water molecules. (c) Shreya is dutiful, friendly with scientific aptitude.

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure

Chapter 11 Force and Pressure Class 8 Science NCERT Solutions

Class 8 science chapter 10 reaching the age of adolescence ncert questions and answers - topics, chapter 11 force and pressure ncert solutions for class 8 science  - notes, chapter 11 force and pressure class 8 science questions and answers - mcq questions with answers.

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NCERT Exemplar Class 8 Science Chapter 11 Force and Pressure

June 20, 2022 by Sastry CBSE

NCERT Exemplar Class 8 Science Chapter 11 Force and Pressure are part of NCERT Exemplar Class 8 Science . Here we have given NCERT Exemplar Class 8 Science Chapter 11 Force and Pressure.

Multiple Choice Questions

Question. 3 During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is (a) force of gravity (b) electrostatic force (c) force of frictio’n . (d) magnetic force Answer. (b) The electrostatic force is responsible for it, since on combing the hair, the comb and hair get oppositely charged.

Question. 5 Two objects repel each other. This repulsion could be due to the (a) frictional force only (b) electrostatic force only (c) magnetic force only (d) either a magnetic or an electrostatic force Answer. (d) The reason for repulsions may be either an electrostatic (in case of similar charges) or a magnetic (in case of similar pole_s) force.

Question. 6 Which one of the following forces is a contact force? (a) Force of gravity (b) Force of friction (c) Magnetic force (d) Electrostatic force Answer. (b) Force of friction is a contact force. It always acts when the bodies are in contact.

Very Short Answer Type Questions

Question. 9 A ball of dough Is rolled into a flat chapatti. Name the force exerted to change the shape of the dough. Answer. The shape of dough is changed due to the muscular force applied by the hand.

Question. 10 Where do we apply a force while walking? Answer. We apply a force on ground while walking and ground applies reaction force on our foot due to which we are able to move forward.

Question. 11 A girl is pushing a box towards East direction. In which direction should her friend push the box SQ that it moves faster in the same direction? Answer. Her friend should push the box towards East direction, so that it will start moving more fast towards East because the magnitude of force increases.

Question. 13 During dry weather, clothes made of synthetic fibre often stick to the skin. Which type of force is responsible for this phenomenon? Answer. The electrostatic force starts working between the cloth made of synthetic fibre and sticks to skin.

Question. 14 While sieving grains, small pieces fall down. Which force pulls them down? Answer. It is the force of gravity which is responsible for the grains to fall down.

Question. 15 Does the force of gravity act on dust particles? Answer. Yes, force of gravity acts on the dust particles.

Question. 16 A gas filled balloon moves up. Is the upward force acting on it larger or smaller than the force of gravity? Answer. The upward force will be greater than the force of gravity.

Question. 17 Does the force of gravitation exist between two astronauts in space? Answer. Yes, there will be gravitational force between the astronauts because every object in universe, whether small or large, exerts a force on every other object, it is the universal law of gravitation.

Short Answer Type Questions

Question. 18 A chapatti maker is a machine which converts balls of dough into chapatties. What effect of force comes into play in this process? Answer. The force on unit area is called pressure, works on the chapaties. This is the pressure which works on the dough balls and make them chapatties with the help of machine.

Question. 21 Two thermocol balls held close to each other but move away from each other, when they are released. Name the force which might be responsible for this phenomenon. Explain. Answer. This is electrostatic force which is created due to the rubbing and since, same charges are induced on two balls, so they move away from each other.

Question. 22 Fruits detached from a tree fall down due to the force of gravity. We. know, that a force arises due to the interaction between two objects. Name the objects interacting in this case. Answer. The interacting objects in this case are: earth and fruits. Earth applies force of gravity on fruit towards its centre. So, fruit falls down.

Question. 23 A man is pushing a cart down a slope. Suddenly the cart starts moving faster and he wants to sloyy it down. What should he do? Answer. Man can do following things: (i) He can start pulling the cart instead of pushing it in order to balance the downward force due to gravity. (ii) He can go the other side by moving himself very fast in the direction of motion and try to slow down the speed of cart by giving an opposite force to the moving cart.

Long Answer Type Questions

Question. 25 An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down? Answer. The archer shoots an arrow by applying muscular force to stretches the string of the bow. When the string is released, it regains its original position that provides the initial force to set the arrow in motion horizontally. The force of gravity that acts on the arrow in the downward direction and hence, the arrow ultimately falls to the ground.

Question. 28 Two women are of the same weight. One wears sandals with pointed heels while the other wears sandals with flat soles. Which one would feel more comfortable while walking on a sandy beach? Give reasons for your answer. Answer. While walking on a sandy surface, one needs the footwears of larger area so that the pressure exerted on the ground is minimum. So, in this case, the woman having the sandals with pointed heels will be less comfortable in walking while the other woman wears sandals with flat soles feels more comfortable while walking on sandy beach.

Question. 29 It is much easier to burst an inflated balloon with a needle than by a finger. Explain. Answer. Because needle tip has very less area of cross-section in comparison to that of our finger and we know that pressure exerted by a force is inversely proportional to the area where it has been applied, so pressure exerted will be more by the needle tip than the finger. –

NCERT Exemplar Class 8 Science Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials : Metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Combustion and Flame
• Chapter 7 Conservation of Plants and Animals
• Chapter 8 Cell Structure and Functions
• Chapter 9 Reproduction in Animals
• Chapter 10 Reaching the Age of Adolescence
• Chapter 11 Force and Pressure
• Chapter 12 Friction
• Chapter 13 Sound
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

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Force and Pressure

1.1 INTRODUCTION A table can be moved from one place to another by either pushing it or pulling it

Similarly, you can open a door by either pushing or pulling it. When a ball is thrown with more force, it travels a longer distance. The shape of a bottle can change when it is squeezed. Also, the direction of a moving ball can change by striking it. Have you wondered how the shape of a bottle changes when squeezed? Or how can the direction of a moving ball change by kicking it in different ways? All the above activities can be associated with pushing or pulling . Therefore, whenever an object is moved, we can say that it has either been pushed or pulled. This push or pull is known as force. In other words, a body moves whenever a force is applied to it. Therefore, a body cannot move unless a force is applied. Apart from push or pull, force is any action that has the tendency to change the position, shape, or size of an object. Everyday actions such as pushing, pulling, stretching, lifting, squeezing, and twisting are also examples of force. Let us try to list some examples of everyday force and see if we can classify them as push or pull. Examples 1. Hitting a cricket ball with a bat 2. Opening a door 3. Plucking a flower 4. Flying a kite 5. Moving a wheel barrow 6. Hitting a tennis ball with a racquet 7. Taking a carrot out of the ground 8. Playing on a swing 9. Picking up a shopping bag 10. Squeezing a toothpaste tube

1.11 NEWTON’S FIRST LAW OF MOTION Let us suppose that a book is lying on a table. It is at rest. Can the book change its position by itself? Obviously, no. The book will not move by itself, unless you push or pull or lift it. Thus, the position of the book can change its position, only when some force is applied. A person riding a bicycle along a level road does not come to rest immediately after he stops pedaling, unless he applies the brakes. Here, on applying the brakes, the state of motion is changed to a state of rest. These examples contribute to Newton’s First law of motion. A body continues to be in the state of rest or of uniform motion along a straight line unless it is compelled by an external force to change its state. “Objects keep on doing what they are doing, unless they are acted upon by an unbalanced force”. The of Newton’s First law of motion introduces the concept of inertia and defines force. Therefore the first law of motion is also known as the law of inertia.

  ∴ 1   n e w t o n   ( N )   =   1   k g   m / s 2   1   d y n e   =   1   g   c m / s 2 Note : i) 1 newton is that much force which produces an acceleration of 1 m/s 2 in a body of mass 1 kg. ii) The force is said to be 1 dyne if it produces 1 cm/s 2 acceleration in a body of 1g mass. Relation between newton and dyne : 1 newton (N) = 1 kg m/s 2 = 1000 g × 100 cm/s 2 = 100000 g cm/s 2 = 10 5 gcm/s 2 = 10 5 dyne

Acceleration Due To Gravity The earth attracts every other body lying near or on its surface towards its centre. The origin of this force between the earth and a body is due to interaction between their masses. The force of attraction exerted by the earth on a body is called gravitational pull or gravity. We know that when force acts on a body, it produces acceleration. Therefore, a body under the effect of gravitational pull must accelerate. The acceleration produced in the motion of a body under the effect of gravity is called acceleration due to gravity. It is denoted by g. The value of acceleration due to gravity near the surface of the earth is 9.8ms -2 . The value of acceleration due to gravity does not depend upon, whether the body falling under gravity is a light one or a heavy one i.e., the value of g is independent of the mass of the body. If ‘g’ is acceleration due to gravity, ‘m’ is the mass of a body; then the gravitational force on the body is ‘mg’ and is called the weight of the body. weight = mass × acceleration due to gravity i.e. W = mg.

PRESSURE 1.16 INTRODUCTION

• Have you ever thought of these:
• How does a glider move in the air?
• Why a sudden outbreak of sand storm blew off the tops of the tents in desert.
• Why the paste comes out from the front end when it is pressed from the rear end?
• Why a camel moves faster than a horse in the desert?
• Why a sharp knife can cut easily in contrast to a blunt knife.
• How could we empty a cool drink bottle using a straw? The answers for these questions can be answered from this topic.

1.17 THRUST All bodies have a certain weight and a certain base area. When a body rests on a surface, it exerts a force equal to its weight, normal to its surface. This force is called thrust. Thrust is the total force or total weight acting normal to the surface. Weight of the body is the product of mass and acceleration due to gravity i.e., W = mg (where ‘g’ is acceleration due to gravity)

 Pressure  ( P ) =  Thrust  ( T )  Area  ( A ) Units: C.G.S. units: dyne/cm 2 or g.wt/cm 2 S.I. units: N/m 2 or kg.wt/m 2 Note: i) The S.I. unit N/m 2 is also known as Pascal. It is denoted by ‘Pa’. ii) The other units of pressure are bar, torr, cm of Hg and mm of Hg. iii) 1 atm = 10 5 Pascal = 10 5 N/m 2 = 10 6 dyne /cm 2 = 76 cm of Hg = 760 mm of Hg = 760 torr iv) Pressure on a body can be exerted from any direction. Hence, it has a no particular direction and is considered as a scalar quantity. Applications of Pressure i) Design of Wheels of different vehicles: Depending on the requirement, wheels of different vehicles are designed accordingly. Two illustrations are cited here under: Double wheel at rear end In general, the weight (force) is more at the rear end of the trucks, buses etc. This results in the development of greater pressure between the tyres and the road. If the pressure is more, the rate of damage is more and it may lead to accidents.

F 1 a 1 = F 2 a 2 = F 3 a 3 = F 4 a 4 = F 5 a 5

where a 2 , a 3 , a 4  and  a 5 are the areas of cross-section of pistons at B, C, D and E respectively. This indicates that pressure is transmitted equally in all directions as stated by Pascal’s law. Application of Pascal’s Law Pascal’s law is used to multiply force in machines such as the hydraulic press or Bramah press, hydraulic lift and hydraulic brake.

Principle of a Hydraulic Machine (Hydraulic Press or Bramah Press) Hydraulic press works on the principle of Pascal’s law. Construction : It consists of two cylindrical vessels X and Y of different cross sections. Let the cross sectional area of X be ‘A 1 ’ and that Y be ‘A 2 ’

=  Area of larger piston   Area of smaller piston  = π R 2 π r 2 = R 2 r 2

MA = (  Radius of larger piston  ) 2 (  Radius of smaller piston  ) 2

Note : i) Larger piston is generally referred as press plunger ii) Smaller piston is referred as pump plunger

Uses of Hydraulic Press 1. It is used for compressing the cotton bales and straw. 2. It is used for extracting oil from oil seeds. 3. It is used for punching holes in metals. 4. It is used for giving specific shapes to metal sheets. 5. It is used for servicing automobiles in service stations. 1.21 ATMOSPHERIC PRESSURE The atmosphere is a mixture of gases. Above the ground, the Earth’s atmosphere extends to a few hundred kilometers in height. Very close to the Earth’s surface, we find millions of gas molecules in every cubic centimeter. It is calculated that roughly around molecules per cubic centimeter are present. These molecules are all zipping around in different directions, colliding into each other and rebounding. They make an impact on each and every object by bombarding their surface resulting in pressure. The weight of the atmosphere also exerts force resulting in pressure. This pressure is known as Atmospheric pressure. The weight of thrust of air exerted on unit area of earth’s surface is called Atmospheric pressure. It is to be noted that the atmospheric pressure decrease as the altitude increases. The reason being that the number of molecules present at a higher altitude is less than the number of molecules present at the sea level. So, as the number of air molecules decreases with increases in altitude, the air pressure also decrease. Measurement of Atmospheric Pressure Atmospheric pressure is measured by using a barometer. It was invented by Torricelli in 1643. “The Mercury Barometer” Measurement of Atmospheric Pressure using Barometer Atmospheric pressure (P) can be obtained by a barometer, using the formula. P = h × d × g Where, ‘h’ is the height of liquid column, ‘d’ is the density of the barometeric liquid and ‘g’ is the acceleration due to gravity. If ‘h’ is expressed in meters, ‘d’ in Kg/m 3 and ‘g’ in m/s 2 , the pressure obtained by this formula is in terms of ‘Newton/m2 or ‘dyne/cm 2 . Pressure measured in this way is called Absolute pressure. In the formula ‘P = hdg’, the terms ‘d’ and ‘g’ for a given barometer are constant and the atmospheric pressure is proportional to the height of the mercury column. 1 atm is the pressure exerted by a vertical column of mercury of 76 cm (or 760 mm) height. ∴ 1 atm = 76 cm × 13.6 g cm -3 × 9.8 ms – 2 (using hdg for pressure exerted by a liquid) = 0.76 m ×13.6 × 10 3 kg m -3 × 9.8 ms – 2 = 101292.8 N m -2 =1.013×10 5 Pa Other units usually used in measurement of pressure are torr and bar 1 torr = 1 mm of Hg, 1 bar = 10 5 Pa 1.22 BUOYANCE A four – year child was questioned. ‘How do you wash your hands’ ? He promptly answered, ‘With the water form the tap’. A twelve – year boy was questioned: How do you get water in your tap ? He answered, ‘We have a storage tank the upstairs, which gets filled up when we switch on the motor’. Okay! This is how, in this modern age, we get water effortlessly. But in most of the villages the situation is entirely different. Even agricultural fields are watered by manual drawing, from wells, leave alone the domestic purpose. For their daily requirements, village people draw water from wells with the help of a bucket tied to a rope. When the bucket is released into the well, it gets filled up with water and then sinks to a certain depth in water. Now, try to pull out the rope and observe. While drawing water form a depth to the surface, we feel that the bucket of water is very light or almost weightless, but when we draw the water from the surface to the required height, we feel some heaviness or weight of water. From this act, it is clear that an object can be raised or lifted easily inside water. Heave you ever thought, what makes this raising or lifting easy ? This is due to the invisible force that is exerted by the liquid on the body in an upward direction. This upward force is called Buoyant force. From the above activity, it is very clear that some invisible force acts in upward direction when the body is immersed in water. This force makes the weight of the body (bucket) less than its actual weight. The loss in weight is caused due to the upward force acting on the body. It is called buoyant force and the property is called buoyancy. The upward force which is acting on a body when it is completely or partially immersed in a fluid is called up thrust or the buoyant force, and the phenomenon is known as buoyancy. Examples of Buoyant Force 1. When we lift a stone in air, we feel it heavier but inside the liquid we feel it to be lighter because water exerts and invisible force (upthrust) on the body, which decreases the weight of the body. That is why we feel it lighter inside the water than in the air. 2. When a swimmer jumps into water from a height, he finds himself being pushed towards the surface of the water without any effort on his part. 3. A stone which is dropped, falls down with an acceleration of 9.8 ms – 2 in the air. The same stone (density = 5 g cm -3 ) moves down in water with an initial acceleration of 7.8 ms – 2 due to upward buoyant force. Cause of Buoyant Force We know that a liquid contained in a vessel exerts pressure at all points and in all directions. According to Pascal’s law, the direction of pressure is normal (perpendicular) to the surface of the body.

The pressure at a given point depends on the depth (h) of the point inside the liquid. (P = hdg) Now, consider a body ABCD inside the liquid, as shown in the figure.

i) Side – wise Pressure : Consider two points ‘x’ and ‘y’ on the sides AD and BC respectively at the same depth as shown in the figure.

ii) Upward and Downward Pressure : The downward pressure acts on the upper surface of the body and an upward pressure acts on its lower surface. The lower face is at a greater depth than the upper face.

1.23 ARCHIMEDES’ PRINCIPLE Two thousand years ago there lived a Greek philosopher, Archimedes’. He was a scientist in the court of a king. The king had a doubt about the purity of gold with which his crown was made. So he asked Archimedes to invent a method of testing the purity of gold without spoiling the crown. One day, Archimedes noticed that when he had entered a fully filled bath tub, some water overflowed. Furthermore, he noticed that he felt considerably lighter in bath the tub. He reasoned that the loss in weight of his body in water must have some connection with the amount of water displaced by his body. He performed a simple experiment and came out with the relation between the apparent loss of weight and the weight of water displaced. This relation is called Archimedes’ principle.

Let us understand it form the following Take a spring balance and suspend 200 g stone to it. The weight of the stone in air is found to be 200 gf. Now, take an empty jar and fill it with water, till the water is one the verge of overflowing.

= W air  – W liquid  = 200 gf – 150 gf = 50 gf

The liquid displaced by the metal block is collected in a beaker and its weight is obtained. Let it be W gf. It is observed that the weight of the liquid displaced is equal to the loss of weight of the object. Weight of liquid displaced (W) = loss of weight W air  – W liquid  We also know, Loss of weight = Buoyant force ________ (2)     ∴ (1) = (2) Hence, we can say that buoyant force is equal to the weight of the liquid displaced. Thus, we can conclude that “Whenever a body is partly or wholly immersed in a fluid, it experiences an upward buoyant force which is equal to weight of the liquid displaced by the body”. This is known as Archimedes’ principle, which, in short, is Buoyant force = weight of liquid displaced Calculation of Buoyant Force We know that buoyant force is equal to the weight of the liquid displaced. Let the weight of the liquid displaced be ‘mg’. Buoyant force (mg) = V × d × g ( ∵ mass = volume × density) V liquid displaced  × d liquid  × g        _____ (1) If the body is inside the liquid, then the volume of the liquid displaced is equal to the volume of the body, Now the equation changes as Buoyant force = V body  × d liquid  × g    _____ (2) V liquid displaced  = V liquid 

i) Buoyant Force and Volume of Body Dip an iron block and a thermocol sheet of the same mass into the water. in which case do you feel the Buoyant force more? We know, buoyant force = V body  × d liquid  × g As they are dipped in the same liquid and at the same place, d liquid  and g are constants. ∴  Buoyant force  ∝ V body  Let us check their volumes. Volume of a body (V) = mass ( m ) density ( d ) As mass is same for both the bodies,  V ∝ 1   d As the density of thermocol is less than that of iron, volume of thermocol is more and therefore, it displaces more volume of water. Therefore, buoyant force is more on the thermocol sheet. Conclusion: If two bodies of the same mass are immersed in water, then the body with greater volume or less density experiences more buoyant force. In other words, the loss of weight is more for the body with greater volume. ii) Buoyant Force and Density of Liquid Take two beakers, one filled with water and the other with oil. Try to observe the loss of weight by immersing the body completely in water and oil separately. In which case do you feel more loss of weight ? The loss of weight can be found out, if buoyant force is known. We know, buoyant force = V body  × d liquid  × g As the same body is immersed at a given place, V body  and g are constant. ∴  Buoyant force  μ   d liquid  Let us check the densities of water and oil. As the density of oil is less than the density of water, buoyant force is more for water. Conclusion: If a body is immersed in water and oil, as the liquid with greater density produces more buoyant force, here, water with greater density produces more buoyant force. iii) Buoyant Force and Gravity Take a body of volume ‘V”, and immerse it in a liquid of density dliquid on the surface of the earth and on the surface of the moon respectively. In which case do you feel the buoyant force more? We know, buoyant force = V body  × d liquid  × g As the body and liquid are the same on both the surfaces, V body   and  d liquid  are constant. ∴  Buoyant force ∝ g Acceleration due to gravity on the earth is six times greater than the acceleration due to gravity on the moon. So, buoyant force is more on the earth than on the moon. Conclusion: A body in a given liquid experiences greater buoyant force at a place with greater value of ‘g’. Planets on which a body experiences highest and least Buoyant Force Of all the planets, the value of ‘g’ is least for Pluto and the planet with greater value of ‘g’ is Jupiter. So, buoyant force for a body in a liquid is the least on Pluto and greater on jupiter. The value of ‘g’ on Saturn is almost equal to that on earth. Hence, buoyant force experienced by a body in a given liquid on Saturn is the same as that on the earth.

1.24 FLOATATION Consider the following cases: Case-1: Stone in water A stone in water is acted upon by two forces as shown.

Case-3: Wood in Water What happens if the weight of the body is equal to the buoyant force ? If the weight of the body is equal to the buoyant force, the body neither sinks like the stone nor moves up like the balloon. But it floats.

Conditions 1. Sinking of a Body

2. Flotation of a Body

1.25 RELATIVE DENSITY Density Density of a substance is defined as its mass per unit volume,

i.e.,  Density  =  mass   volume 

The SI unit of density is kg m -3 . Its CGS unit is gcm -3 . Let us consider mercury of density 13.6 g cm -3 , alcohol of density 0.8 g cm -3 and aluminium of density 2.7 g cm -3 . If you compare the densities of mercury and aluminium, aluminium has less density than mercury, whereas if you compare aluminium and alcohol, aluminium is denser than alcohol. In this way, any substance can be heavier or lighter when compared to the other substance. To avoid this confusion, another term is devised, which is called relative density. In relative density, the density of a substance is compared to the density of water at 4 °C. The relative density of a substance is the ratio of the density of the substance to the density of water at 4°C. Relative density of a substance

=  Density of the substance   Density of water at  4 ° C _____ (1)

Note: i) Relative density is also known as specific gravity. ii) Relative density is the ratio of densities. So, it has no unit, but is a pure number. Significance of Relative Density Relative density of a substance tells us how many times a substance is denser than water. Example: If the relative density of a substance is ‘6’, it means that the substance is 6 times denser than water. Relative Density in terms of Weight of Body and Weight of Water displaced by the Body

We know, Relative density =  Density of substance   Density of water 

Relative Density = m substance  V substance  m water  V water 

If the volume of a substance is equal to the volume of the water, then, Relative density =  Mass of any volume of substance   Mass of water of an equal volume 

Multiplying the numerator and the denominator by ‘g’, then, we get, Relative density =  Mass of any volume of substance  × g  Mass of water of an equal volume  × g

∵   Relative   density   of   a   substance   ( or   body )

=  weight of any volume body in air   weight of equal volume of water  _____ (2)

We know that the weight of equal volume of water is equal to the loss of weight of the body in water. Loss of weight in water = Weight in air – Weight in water = Weight of water displaced _________ (3) Using (2) and (3), we can write

Relative density of a body =  weight of the body   loss of weight of the body in water  _________ (4)

Relative density of a body =  weight of the body in air   weight of the body in air – weight of the body in water  _________ (5)

Determination of Specific Gravity or Relative Density of Liquids Take a body which sinks in both the liquid and the water. Determine its weight in air, let it be W 1 . Now, determine its weight in the given water and liquid with a spring balance. Let it be W 2 and W 3 respectively. The body displaces the liquid equal to its volume(V) Loss of weight of the body in water = Weight of the body in air – Weight of the body in water = W 1 – W 2 Loss of weight of the body in the given liquid = weight of the body in air – weight of the body in liquid = W 1 – W 3

Relative density of liquid = w e i g h t   o f   ‘ V   ‘   v o l u m e   o f   l i q u i d w e i g h t   o f   ‘ V   ‘   v o l u m e   o f   w a t e r

But, we know that the weight of V volume of liquid = loss of weight of the body in liquid. Similarly, weight of ‘V’ volume of water = loss of weight of the body in water.

Relative density = L o s s   o f   w e i g h t   o f   t h e   b o d y   i n   l i q u i d   L o s s   o f   w e i g h t   o f   t h e   b o d y   i n   w a t e r

Relative density = W 1 – W 3 W 1 – W 2

By substituting the measured values of W 1 ,   W 2 , the relative density of the liquid can be determined.

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MCQs on Force and Pressure Questions for Class 8 with Answers

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In Class 8 Science, understanding force and pressure is important. Multiple Choice Questions (MCQs) help check and improve knowledge. These MCQs cover key topics like how force and pressure are related, how they are measured, and how they are used. You can find MCQs on force and pressure for Class 8 t o help you learn and remember these science basics. For extra help, you can get MCQs with answers for class 8 , even in PDF format.

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Force and Pressure for Class 8 with Answers

Ques. Which of the following is a contact force?

A) Gravitational force

B) Magnetic force

C) Frictional force

D) Electrostatic force

Ans: C) Frictional force

Ques. The force that opposes the motion of an object is called:

A) Friction

D) Normal force

Ans: A) Friction

Ques. The SI unit of force is:

Ans: A) Newton

Ques. Pressure is defined as:

A) Force per unit area

B) Force per unit volume

C) Work done per unit area

D) Work done per unit volume

Ans: A) Force per unit area

Ques. Which of the following is a scalar quantity?

B) Pressure

C) Velocity

D) Acceleration

Ans: B) Pressure

Ques. When a force is applied on an object in the direction of its motion, it:

A) Increases its speed

B) Decreases its speed

C) Changes its direction

D) Stops moving

Ans: A) Increases its speed

Ques. The force exerted by a liquid on an object immersed in it is called:

A) Buoyant force

C) Friction

Ans: A) Buoyant force

Ques. The force of gravity acting on an object is also known as:

Ans: A) Weight

Ques. Which of the following is an example of a non-contact force?

B) Friction

C) Magnetic force

Ans: C) Magnetic force

Ques. The pressure exerted by a liquid depends on:

A) The depth of the liquid

B) The density of the liquid

C) Both depth and density of the liquid

D) Neither depth nor density of the liquid

Ans: C) Both depth and density of the liquid

Ques. The force that acts on an object in a direction opposite to its motion through a fluid is called:

B) Drag force

Ans: B) Drag force

Ques. The pressure at a point in a fluid is:

A) The same in all directions

B) Higher in the horizontal direction

C) Lower in the vertical direction

D) Dependent on the shape of the container

Ans: A) The same in all directions

Ques. Which of the following is an example of a balanced force?

A) Pushing a heavy box

B) Tugging a rope in opposite directions

C) Holding a book stationary on a table

D) Kicking a football

Ans: C) Holding a book stationary on a table

Ques. The force required to keep an object moving at a constant speed is:

A) Frictional force

C) Net force

Ans: A) Frictional force

Ques. The force that opposes the relative motion between two surfaces in contact is called:

A) Normal force

D) Buoyant force

Ans: C) Friction

Ques. The pressure exerted by a gas depends on:

A) Its temperature

B) Its volume

C) Both temperature and volume

D) Neither temperature nor volume

Ans: C) Both temperature and volume

Ques. The force exerted by a stretched spring is an example of:

C) Elastic force

Ans: C) Elastic force

Ques. The force that acts on an object at rest on a surface is:

C) Normal force

Ans: C) Normal force

Ques. The pressure at the bottom of a container filled with liquid is highest because of:

A) Atmospheric pressure

C) Depth of the liquid

D) Density of the liquid

Ans: C) Depth of the liquid

Ques. The force that keeps an object moving in a circular path is called:

A) Centripetal force

B) Centrifugal force

D) Friction

Ans: A) Centripetal force

Ques. The pressure exerted by a solid object on a surface depends on:

A) Its mass

B) Its area of contact

C) Both mass and area of contact

D) Neither mass nor area of contact

Ans: C) Both mass and area of contact

Ques. The force that acts on an object due to the Earth’s gravitational pull is called:

Ans: D) Weight

Ques. The force that acts on an object when it is pushed or pulled is called:

D) Applied force

Ans: D) Applied force

Ques. The pressure exerted by a liquid on the walls of a container is:

A) Constant

B) Increases with depth

C) Decreases with depth

D) Depends on the shape of the container

Ans: B) Increases with depth

Ques. The force that acts on an object when it is lifted is called:

Ans: A) Tension

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