Lesson: Force and Pressure
Exercise:

# Question: 1

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

## Solution:

Two examples of push force are as follows:

·         Moving a box from one place to another on a table.

·         A player kicks a football using his foot.

Two examples of pull force are as follows:

·         Opening a drawer.

·         A fishing net is pulled to draw fish from sea.

# Question: 2

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

## Solution:

Two examples of situations in which applied force causes a change in the shape of an object are as follows:

·         Making of chapatti from the dough

·         Stretching a rubber band

# Question: 3

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.

## Solution:

(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 push or pull it.
(d) The north pole of a magnet repels the north pole of another magnet.

# Question: 4

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.

## Solution:

(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.

# Question: 5

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.

## Solution:

(a)   Agent exerting the force $–$ Fingers
Object on which force acts $–$ Lemon
Effect of force $–$ Change in shape of lemon

(b)   Agent exerting the force $–$ Fingers
Object on which force acts $–$ toothpaste tube
Effect of force $–$ Change in shape of toothpaste tube.

(c)   Agent exerting the force $–$ Load
Object on which force acts $–$ Spring
Effect of force $–$ Change in shape of spring.

(d)   Agent exerting the force $–$ Muscles of Athlete
Object on which force acts $–$ Athlete’s body
Effect of force $–$ Athlete jumps over the bar.

# Question: 6

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

## Solution:

A blacksmith uses his muscular force to hammer a hot piece of iron. His muscular force changes the shape of the iron so that the desired shape can be given to the hot piece of iron.

# Question: 7

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

## Solution:

When a balloon is rubbed with a synthetic cloth, it gets charged. When the charged balloon is placed near a wall, a force is exerted by the charged balloon on the uncharged wall. The attraction force between the balloon and the wall is due to the electrostatic force.

# Question: 8

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.

## Solution:

In this case, the force of gravity is acting in downward direction and the muscular force is acting in upward direction. Both the forces are acting in opposite directions, hence nullifying the effect of each other. Thus, there is no change in the state of motion of the bucket.

# Question: 9

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.

## Solution:

There are two forces acting on the rocket,

a)      Gravitational force which pulls the rocket towards the ground

b)      The force of friction 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, 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
(a) pressure of water
(b) gravity of the earth
(c) shape of rubber bulb
(d) atmospheric pressure

## Solution:

(d) Atmospheric pressure