Class 8 Science

Chapter 5 Solutions — Exploring Forces

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Solutions

Overview

Step-by-step NCERT solutions for Exploring Forces (Chapter 5, NCERT Class 8 Science) — every question and answer worked out in full, not just the final result. You can also read the Exploring Forces textbook chapter.

Solved

What these solutions cover

All 10 questions in Exploring Forces are solved in the PDF. Here's what's inside, exercise by exercise:

Keep the Curiosity Alive

1.
Match items in Column A with the items in Column B. Column A (Type of force) | Column B (Example)
- (i) Muscular force |
- (a) A cricket ball stopping on its own just before touching the boundary line
- (ii) Magnetic force |
- (b) A child lifting a school bag
- (iii) Frictional force |
- (c) A fruit falling from a tree
- (iv) Gravitational force |
- (d) Balloon rubbed on woollen cloth attracting hair strands…
2.
State whether the following statements are True or False.
- (i) A force is always required to change the speed of motion of an object.
- (ii) Due to friction, the speed of the ball rolling on a flat ground increases.
- (iii) There is no force between two charged objects placed at a small distance apart.
Two balloons rubbed with a woollen cloth are brought near each other. What would happen and why?
When you drop a coin in a glass of water, it sinks, but when you place a bigger wooden block in water, it floats. Explain.
5.
If a ball is thrown upwards, it slows down, stops momentarily, and then falls back to the ground. Name the forces acting on the ball and specify their directions.
- (i) During its upward motion
- (ii) During its downward motion
- (iii) At its topmost position
6.
A ball is released from the point P and moves along an inclined plane and then along a horizontal surface as shown in Fig. 5.16. It comes to stop at the point A on the horizontal surface. Think of a way so that when the ball is released from the same point P, it stops
- (i) before the point A
- (ii) after crossing the point A.
Why do we sometimes slip on smooth surfaces like ice or polished floors? Explain.
Is any force being applied to an object in a non-uniform motion?
The weight of an object on the Moon becomes one-sixth of its weight on the Earth. What causes this change? Does the mass of the object also become one-sixth of its mass on the Earth?
10.
Three objects 1, 2, and 3 of the same size and shape but made of different materials are placed in the water. They dip to different depths as shown in Fig. 5.17. If the weights of the three objects 1, 2, and 3 are w_1, w_2, and w_3, respectively, then
- (i) w1 = w2 = w3
- (ii) w1 > w2 > w3
- (iii) w2 > w3 > w1
- (iv) w3 > w1 > w2

Sample

Worked examples

3 questions from Exploring Forces, solved step by step.

Keep the Curiosity Alive

Two balloons rubbed with a woollen cloth are brought near each other. What would happen and why?

When a balloon is rubbed with a woollen cloth, static electric charges build up on its surface. Both balloons are rubbed in the same way with the same material, so both acquire the same kind of charge.

When two similarly charged objects are brought near each other, like charges repel.

Therefore, the two balloons will repel each other and move away from each other.

The force responsible is the electrostatic force, which is a non-contact force that acts even without physical contact between the charged objects.

Answer: The two balloons will repel each other and move apart, because both acquire the same kind of static charge after rubbing with wool, and like charges repel.

Keep the Curiosity Alive

When you drop a coin in a glass of water, it sinks, but when you place a bigger wooden block in water, it floats. Explain.

Two forces act on any object placed in a liquid: the gravitational force (weight) acting downward, and the buoyant force (upthrust) applied by the liquid acting upward.

For the coin:

A coin is made of metal (dense material). Its weight is much greater than the buoyant force exerted by the water on it. Since the downward gravitational force exceeds the upward buoyant force, the coin sinks.

For the wooden block:

Wood is less dense than water. Even though the wooden block is bigger and may weigh more in absolute terms, when placed in water it displaces a volume of water whose weight equals (or exceeds) the block's own weight before the block is fully submerged. At that point, the upward buoyant force balances the downward gravitational force, so the block floats.

In summary: an object floats when the buoyant force equals its weight; it sinks when its weight exceeds the buoyant force.

Answer: The coin sinks because its weight (gravitational force) is greater than the buoyant force water exerts on it. The wooden block floats because the buoyant force from the water equals its weight before the block is fully submerged, so the two forces balance.

Keep the Curiosity Alive

If a ball is thrown upwards, it slows down, stops momentarily, and then falls back to the ground. Name the forces acting on the ball and specify their directions. (i) During its upward motion (ii) During its downward motion (iii) At its topmost position

(i) During upward motion:

Gravitational force acts on the ball in the downward direction (towards the Earth). Air resistance (friction of air) also acts in the downward direction, opposing the upward motion. The combined effect of these forces opposes the ball's upward movement, causing it to slow down.

(ii) During downward motion:

Gravitational force acts on the ball in the downward direction (towards the Earth), which is now in the direction of motion — this accelerates the ball. Air resistance acts in the upward direction, opposing the downward motion.

(iii) At the topmost position:

The ball is momentarily at rest. Gravitational force still acts on the ball in the downward direction. This unbalanced downward force causes the ball to begin moving downward. There is no air resistance at this instant since the ball has zero velocity.

Answer: (i) Upward motion — gravitational force (downward) and air resistance (downward). (ii) Downward motion — gravitational force (downward) and air resistance (upward). (iii) Topmost point — gravitational force (downward) only.

All 10 questions in Exploring Forces are solved step by step in the Solutions PDF above.

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Chapter 5 Solutions — Exploring Forces

Overview

What these solutions cover

Keep the Curiosity Alive

Worked examples

Two balloons rubbed with a woollen cloth are brought near each other. What would happen and why?

When you drop a coin in a glass of water, it sinks, but when you place a bigger wooden block in water, it floats. Explain.

If a ball is thrown upwards, it slows down, stops momentarily, and then falls back to the ground. Name the forces acting on the ball and specify their directions. (i) During its upward motion (ii) During its downward motion (iii) At its topmost position

More solutions in Curiosity

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