NCERT Solutions for Class 8 Science Chapter 8 Force and Pressure

NCERT
SOLUTIONS
CLASS - 8TH

aglase .co

Class : 8th
Subject : Science
Chapter : 11
Chapter Name : FORCE AND PRESSURE

Q1 Give two examples each of situations in which you push or pull to change the state of motion of
objects.?

Answer. Two examples of push force are as follows:
(i) A heavy box at rest is pushed to move it from one room to another. This changes the state of
motion of the box.
(ii) A player pushes a football using his foot. This changes the state of motion of the ball.
Two examples of pull force are as follows:
(i) Rope is pulled to draw water from a well. This changes the state of motion of the water bucket.
(ii) A drawer is pulled to open it. This changes the state of motion of the drawer.

Page : 142 , Block Name : Exercise

Q2 Give two examples of situations in which applied force causes a change in the shape of an
object.

Answer.Two examples of forces that cause a change in the shape of an object are as follows:
(i) Squeezing of a plastic bottle changes the shape of the bottle.
(ii) Deformation of clay by pressing it between the hands.

Page : 142 , Block Name : Exercise

Q3 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.

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

Page : 142 , Block Name : Exercise

Page 1 of 3 Aglasem Schools

Book : Science Ncert Solutions | Chapter-11 Science

Q4 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 ll 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.

Answer. (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.

Q5 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 ngers 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 xed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.

Answer. (a) In squeezing a piece of lemon, we make use of muscular force to extract its juice. This
muscular force acts on the lemon. As a result, the shape of the lemon gets changed.
(b) We use our muscular force to take out paste from a toothpaste tube. The muscular force acts on
the toothpaste tube. As a result, the shape of the tube gets changed.
(c) Here, the suspended load exerts a force on the spring and pushes the spring downwards. As a
result, the spring gets stretched. Hence, its shape gets changed.
(d) An athlete pushes the ground with his feet. His feet exert a muscular force on the ground. This
allows him to jump over the bar. As a result, his state of motion gets changed.

Q6 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. When a blacksmith hammers a hot piece of iron, he uses his muscular force. This
muscular force changes the shape of the iron so that it can be given a desired shape.

Page 2 of 3 Aglasem Schools

Q7 An in ated 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?

Answer. On rubbing an in ated balloon with a piece of synthetic cloth, it becomes charged. A
charged body attracts an uncharged body. When this charged balloon is pressed against a wall, it
sticks to the wall. The force acting between the charged balloon and the wall is the electrostatic
force.

Q8 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.

Answer. We make use of muscular force to hold a 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 but opposite in direction. Therefore, the net force on the bucket is zero.
Hence, there is no change in its state of motion.

Q9 A rocket has been red upwards to launch a satellite in its orbit. Name the two forces acting on
the rocket immediately after leaving the launching pad.

Answer. The two forces acting on the rocket are the force of gravity, which pulls the rocket towards
the ground, and the force of friction due to earth's atmosphere, which opposes its motion.

Q10 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 lled 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.

Answer. (d) The rise of water in the dropper is due to atmospheric pressure. The rise of water in a
dropper is due to atmospheric pressure. When all the air escapes from the nozzle, the atmospheric
pressure, which is acting on the water, forces the water to ll the nozzle of the dropper.

Page 3 of 3 Aglasem Schools