Important Questions Class 8 Science Chapter 11

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. 

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.

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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.

Answer 1

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

1. The Pull situations are- 
2. 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.
3. 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.
4. The Push Situations are
5. 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.
6. 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.

Answer 2

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

1. i) By pressing the clay between our hands, it deforms.
2. 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.

Answer 3

(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

Answer 4

1. 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.
2. 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.

1. 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?

Answer 5

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?

Answer 6

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.

Answer 7- 

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.

Answer 8

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

Answer 9

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.

Answer 10

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

Answer 11

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

Answer 12

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?

Answer 13

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.

Answer 14

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.

Answer  15

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.

Answer 16

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.

Answer 17

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.

Answer 18

 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-

1. 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-

1. 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.
2. b) Electrostatic Force: The force applied by a charged body to another charged or uncharged body is called electrostatic force.
3. 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?

Answer  22

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- 

Force can

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”?

Answer 24

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?

Answer 25

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?

Answer 26

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

1. a) May move the object.

1. b) Change the shape of an object and may move the object.

1. c) May stop a moving object.

1. 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.

1. 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.

1. 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.

Answer 33:

 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:

1. The shape of an object can be changed.

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

1. 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.

1. 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.

1. 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-

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