GSEB Class 8 Science Solutions Chapter 11 Force and Pressure

Question 1. Give two examples of each of the situations in which you push or pull to change the state of motion of objects.
Answer: We push a bicycle to make it move forward. We pull a table to change its position.
In simple words: To make a bicycle go, we push it. To move a table, we pull it to a new spot.

Exam Tip: When providing examples, make sure they clearly illustrate either a 'push' or a 'pull' action and the resulting change in motion or position of the object.

Question 2. Give two examples of situations in which applied force causes a change in the shape of an object.
Answer: When we press the foam, its shape changes. When we stretch a rubber band, its shape also changes.
In simple words: Pushing foam makes it change shape. Pulling a rubber band also changes its shape.

Exam Tip: Think of materials that are easily deformable when force is applied, like clay, dough, or sponges, for good examples.

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.
Answer:
(a) apply force
(b) attracts
(c) push
(d) repels
In simple words: To get water from a well, you need to use force on the rope. A charged object pulls an uncharged object towards it. To move a heavy cart, you must push it. The north end of one magnet pushes away the north end of another magnet.

Exam Tip: Understand the basic actions of forces (push, pull, attract, repel) and how they apply in different scenarios involving objects, charges, and magnets.

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 it's
(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 air.
Answer:
(a) shape
(b) muscular
(c) contact
(d) gravity, friction
In simple words: When the archer pulls the bow, its shape changes. The force from the archer's muscles is called muscular force. The force that changes the arrow's movement is a contact force. As the arrow flies, gravity pulls it down, and air friction slows it.

Exam Tip: Distinguish between contact and non-contact forces, and remember that forces can change an object's shape, speed, or direction of motion.

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.
Answer:
(a) The fingers are the agents; the lemon is the object. The force's effect is that lemon juice is expelled by squeezing.
(b) The hand is the agent; a toothpaste tube is an object. The force's effect is the paste coming out from the toothpaste tube.
(c) The suspended load is the agent; the spring is the object. The force's effect is the spring elongating due to the load's suspension.
(d) The athlete is the agent; the bar is the object. The force's effect is the jump.
In simple words: (a) Your fingers push the lemon, and juice comes out. (b) Your hand squeezes the tube, and paste comes out. (c) A weight pulls the spring, making it stretch longer. (d) The athlete pushes off the ground to jump over the bar.

Exam Tip: Clearly identify who or what is performing the action (agent) and what is being acted upon (object). Then, describe the specific result of that action.

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?
Answer: The force from hammering changes the shape of the iron. This allows the iron to be molded into the shape of the desired tool.
In simple words: The hammering force helps to reshape the hot iron, making it possible to form it into the tool needed.

Exam Tip: Recall that forces can change an object's shape, especially when the object is malleable like hot metal.

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?
Answer: Electrostatic force.
In simple words: When the balloon is rubbed, it gets an electric charge. This charge creates an electrostatic force that makes it stick to the wall.

Exam Tip: Remember that rubbing certain materials together can transfer electrons, creating static electricity and resulting in electrostatic attraction or repulsion.

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.
Answer: Muscular and gravitational forces act on the plastic bucket. The force acting on the bucket does not cause a change in its state of motion because these forces act in opposite directions with equal magnitudes. Consequently, the net force on the bucket remains zero.
In simple words: Your muscles push up on the bucket, and gravity pulls it down. These two forces are equal and opposite, so they cancel each other out. This means the bucket doesn't move up or down, staying still.

Exam Tip: For an object to remain stationary or move at a constant velocity, the net force acting on it must be zero, meaning all forces are balanced.

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.
Answer:
(i) Gravitational force
(ii) Force of friction.
In simple words: Right after the rocket lifts off, two main forces are working on it: Earth's gravity pulling it down, and friction from the air pushing against it.

Exam Tip: Understand that even after launch, gravity always acts on an object, and air resistance (friction) is present as long as the object moves through the atmosphere.

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 dropper. The rise of water in the dropper is due to
(a) pressure of water
(b) gravity of the earth.
(c) the shape of a rubber bulb.
(d) atmospheric pressure.
Answer: (d) atmospheric pressure
In simple words: When you let go of the dropper bulb, the air pressure outside pushes the water up into the dropper, because the pressure inside the dropper is lower.

Exam Tip: Remember that atmospheric pressure is a significant force and is responsible for many everyday phenomena, including how droppers, straws, and vacuum cleaners work.