Force and Pressure Class 8 Extra Questions and Answers

These AP 8th Class Physics Important Questions and 1st Lesson Force and Pressure Class 8 Extra Questions will help students prepare well for the exams.

Class 8 Science Force and Pressure Extra Questions

Force and Pressure Class 8 Important Questions

Question 1.
What is force ?
Answer:
The push or pull of an object is called force.

Question 2.
What is muscular force ?
Answer:
The force resulting due to the action of muscles is known as the muscular force.

Question 3.
What is contacting force ?
Answer:
The force results when there is a direct physical contact between two interacting objects is called contacting force.

Question 4.
What is friction ?
Answer:
The resistance to the movement of a body over the surface of another body is called friction.

Question 5.
What is magnetic force ?
Answer:
The force exerted by a magnet on another magnet is called magnetic force.

Question 6.
What is a gravitational force ?
Answer:
The attractive forces between any two massive objects is called gravitational force.

Question 7.
What is electrostatic force ?
Answer:
The force exerted by a charged body on other charged or uncharged body is called electrostatic force.

Question 8.
What is pressure ?
Answer:
The force acting on a unit area of a surface is called pressure.

Question 9.
What is atmospheric pressure ?
Answer:
The pressure exerted by,air around us is known as atmospheric pressure.

Question 10.
Why do tools meant for cutting always have sharp edges ?
Answer:
The tools meant for cutting have sharp edges because of smaller contact area they exerts more pressure on objects and cutting of objects are easy.

Question 11.
When a boy jumps from a branch of tree, what forces act on him ?
Answer:

1. The gravitational force
2. The muscular force

Question 12.
How do you increase the pressure by keeping (a) area unchanged and (b) force unchanged ?
Answer:

1. by increasing the force
2. by decreasing the area

Question 13.
What about repulsion between similar poles of two magnets ? Is it a pull or push ?
Answer:
As it is a non-contact force, so it is neither pull or push. It is called as magnetic repulsive force.

Question 14.
What happens to the air in the bicycle tube, when it has a puncture ?
Answer:
Air exert pressure on the walls of the tube. When it gets puncture, air of the tube comes out rapidly.

Question 15.
Can you lift or push a book lying on a table without touching it ?
Answer:
No, we cannot lift or push a book lying on a table without touching it because lifting or pushing is a type of contact forces.

Question 16.
What is non- contact force? Give examples.
Answer:
The force exerts on an object without contact it is called non-contact force.
Eg : 1.Gravity 2. Magnetic force 3. Electrostatic force.

Question 17.
A ball was rolled on a playground. The ball stops after a certain distance.
a) What force is responsible for the ball stopping ?
b) Describe the force in your own words.
Answer:
a) The force responsible for changing the state of motion of the ball is the force of friction.

b) Friction is a force that resists motion between two surfaces that are in contact with each other. The force of friction arises due to contact between surfaces. The force of friction between the surface of the ball and the ground brings the moving ball to rest.

Force and Pressure Extra Questions

Question 1.
Give two examples each for a contact force and a non-contact force.
Contact force :
e.g. 1) Muscular force
2) Frictional force

Non-contact force :
e.g. 1) Magnetic force
2) Electrostatic force

Question 2.
Find net forces from the following diagrams.

Answer:
a) Net force is 3N along horizontal direction towards right.
b) Net force is 10 N along horizontal direction towards right.
c) Net force is zero.
d) Net force is 2N upwards in vertical direction.

Question 3.
Distinguish bepreen a Contact force and a Non-contact force.
Answer:

Contact force	Non-contact force
1) Force which results when there is a direct physical contact between two interacting objects;	1) The force which occurs without any physical contact between two objects is known as a non-contact force.
2) The two objects have direct contact.	2) No contact.
3) ex : Pushing a bicycle.	3) ex.: The attraction of two magnets.

Question 4.
Imagine that Motion has disappeared from the earth. What will happen ? Explain.
Answer:
If friction has disappeared from the earth, then

1. we cannot walk or run.
2. we will not be able to hold the things.
3. vehicles will not move if they are in rest. Vehicles will not stop if they are in motion.
4. no building could be constructed.
5. it will not be possible to write with pen or pencil.
6. we could not fix nail on the wall.

Question 5.
Give two daily life examples each of situations in which you push or pull to change the state of motion of object.
Push :

1. Hitting a football with leg.
2. Moving a loaded cart.

Pull :

1. Opening a door
2. Moving a table towards you

Question 6.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:

1. Pressing a sponge
2. Stretching of rubber band

Question 7.
What changes can be observed when we apply force on an object ?
Answer:

1. Change in the shape of the object.
2. Change in direction of motion of an object.
3. Change in speed of an object if the object is moving.
4. Movement of an object from rest.

Question 8.
Give examples of force exerted by muscles in our body ?
Answer:

1. Inhalation and exhalation of air by lungs.
2. Blood circulation in our body.
3. We push an object like a school bag or lift a bucket of water.

Question 9.
Have you ever seen a game of tug of war ? In this game two teams pull a rope in opposite direction. But sometimes the rope does not move, explain why.
Answer:

1. When two forces acts on an object in opposite direction then the net force is difference of two forces.
2. If two teams pull the rope with equal force, the forces will be in opposite direction and will cancel with each other and the rope wili not move.

Question 10.
Does application of force can only change the speed of an object ?
Answer:
No, on the application of force, the shape of a body may also changes. If force acts in the direction of velocity, it increases its speed and if it acts opposite to the direction of velocity, it decreases its speed.

Question 11.
What is a force ? When can we be sure that a net force is actiug on a body ?
Answer:

1. A push or a pull on an object is called a force.
2. We can be sure that a net force is acting on a body when the body changes its state of motion or direfction of motion or shape.

Question 12.
If a force is applied on a wheel at a point as shown in the figure which makes it roll on the ground, then where is the force of friction acting ?

Answer:
The force of friction acting between the wheel and the ground at the point of contact.

Question 13.
Give a scientific explanation for the following.
A porter (coolie) keeps a round piece of cloth before lifting a heavy load.
Answer:

1. According to the pressure definition, area of a surface is increased then the pressure is decreased.
2. So a porter keeps a round piece of cloth to increase the surface area.
3. That’s why the heavy load is been carried by him easily.

Extra Questions of Force and Pressure Class 8

Question 1.
Observe the vessels A, B, C and D as shown in figure carefully.

Volume of water taken each vessel is as shown. Arrange them in the order or decreasing pressure at the base of each vessel. Explain.
Answer:
Pressure at depth due to liquid column depends upon

1. gravitational acceleration (g)
2. density of liquid
3. height of liquid

And in this case, g and density are same. so only thing that can change pressure is height.
So, the order of pressure exerted by the fluid A, B, C and D at the base is given by P_D > P_B > P_A > P_C.

Question 2.
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 which walking on a sandy beach ? Give reasons for your answer.
Answer:

1. While walking on a sandy surface, one needs the foot wears of larger area.
2. So, that pressure exerted on the ground is minimum.
3. So, in this case, the woman having the sandals with pointed heels will be less comfortable in walking.
4. While the other woman wears sandals with flat soles feels more comfortable while walking on sandy beach.

Question 3.
Design and conduct experiment to test few ways how friction may be reduced.
Answer:
Friction is due to the roughness of surfaces. It can be reduced by the following methods.

1. By polishing the rough surface
2. By applying lubricants like oil and grease to the surfaces.
3. By spreading powder on the rough surface like carrom board.
4. By using soap and detergent solutions, etc.

Experiment: The rusted pulley makes a rattling noise. By applying some oil in between the wheel and axle, the sound in reduced and now it works smoothly.

Question 4.
IdentifyIng actions as push or pull.

Answer: