# NCERT Solutions for Class 8 Science Chapter 11 - Force and Pressure

##### Question 1:

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

(a) A batsman hitting a ball (Push)
(b) Drawing water from a well (Pull)

##### Question 2:

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

(a) Pressing a lump of dough on a plate.
(b) A spring fixed in the seat of a bicycle pressed down due to the weight of the rider.

##### Question 3:

To draw water from a well we have to _____________ the rope.

Pull

##### Question 4:

A charged body _____________ an uncharged body towards it.

Attracts

##### Question 5:

To move a loaded trolley we have to _____________ it.

Push or pull

##### Question 6:

The north pole of a magnet _____________ the north pole of another magnet.

Repels

##### Question 7:

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

Shape

##### Question 8:

The force applied by the archer to stretch the bow is an example of __________ force.

Muscular

##### Question 9:

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

Contact

##### Question 10:

While the arrow moves towards the target, the forces acting on it are due to __________ and that due to __________ of air.

Gravity, friction

##### Question 11:

In the following situations identify the agent exerting the force and the object on which it acts. State the effect of force in each case.
(a) Squeezing a piece of lemon between your 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

##### Question 12:

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 force applied by the hammer ﬂattens the piece of iron, i.e., it changes its shape and size.

##### Question 13:

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 sticks to the wall. What force might be responsible for attraction between the balloon and the wall?

Electrostatic force is responsible for the attraction between the balloon and the wall.

##### Question 14:

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.

Forces acting on the plastic bucket are:
(i) Force of gravity acting downwards
(ii) The muscular force of arms acting upwards
The two forces do not bring any change in the state of motion of the bucket because both these forces are equal in magnitude and opposite in direction. Thus, they cancel each other and the net force on the bucket is zero.

##### Question 15:

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 the rocket leaves the launching pad, the following forces act on it:
(i) Gravitational force of the Earth which pulls rocket towards the ground.
(ii) Frictional force due to the Earth’s atmosphere which opposes its motion.

##### Question 16:

When we press the bulb of a dropper with its nozzle in water, 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:

1. Pressure of water
2. Gravity of the Earth
3. Shape of rubber bulb
4. Atmospheric pressure