NCERT Solutions Class 8 Science
The NCERT Solutions in English Language for Class 8 Science Chapter – 11 (Force and Pressure) has been provided here to help the students in solving the questions from this exercise.
Chapter – 11 (Force and Pressure)
1. Give two examples each of situations in which you push or pull to change the state of motion of objects.
Answer – Examples of situations in which you push or pull to change the state of motion of objects are –
Two examples of push:
1. Dislodging a large block from its initial location by pushing it.
2. We push the door in order to open the door.
Two examples of pull:
1. A bucket of water being pulled from a well.
2. Playing tug of war while pulling ropes.
2. Give two examples of situations in which applied force causes a change in the shape of an object.
Answer – The forces which change the shape of an object are as follows:
1. Stretching the rubber band, changes its shape.
2. Plastic bottles change their shape when squeezed.
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.
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 pull or push it.
(d) The north pole of a magnet repels the north pole of another magnet.
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
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.
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.
Answer – The fingers are the agents, lemon is the object. The effect of force is the lemon juice being expelled by squeezing.
(b) Taking out paste from a toothpaste tube.
Answer – The hand is the agent, toothpaste tube is object and the coming out of the paste from toothpaste tube is the effect of force.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
Answer – Suspended load is agent, spring is the object, the effect of force can be seen in the form of elongation of spring on suspension of load.
(d) An athlete making a high jump to clear the bar at a certain height
Answer – Athlete is the agent, bar is the object. The force can be seen in the form of jump.
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?
Answer – A blacksmith uses their muscular force while hammering a hot piece of iron. The muscular force changes the shape of the iron so that it can be given the desired shape.
7. 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 stuck to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer – Electrostatic force. On the rubbing an object to get charged (static charge) and unlike charges get attracted to each other, such type of force is Electrostatic force.
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.
Answer – Gravitational and muscular forces are acting on a plastic bucket. The forces acting on the bucket do not bring a change in its state of motion because muscular force acts upward direction and gravitational force acts downward direction. Hence net force on bucket is zero.
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.
Answer – The force of gravity is the one which acts on the rocket to pull it towards the ground, and the other one is the force of friction due to the earth’s atmosphere, which opposes its motion.
10. When we press the bulb of a dropper with its nozzle kept in water, the 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
Answer – (d) atmospheric pressure
