Class 6,ch- 3 Force

📘 Subjective Questions – Detailed Answers

1. State the effects of a force on a stationary body and a moving body.

When applied to a stationary body, it can make the object start moving.
When applied to a moving body, it can:
– Change its speed (increase or decrease)
– Change its direction
– Stop it completely

2. Distinguish between a contact and a non-contact force.

Contact Force	Non-contact Force
1.Acts only when objects touch	1.Acts without any physical contact
(Example: Friction, muscular force)	(Example: Gravity, magnetic force)
2.Needs direct interaction	2.Works even from a distance

3. Distinguish between static and rolling friction.

Static Friction	Rolling Friction
1.Acts on a stationary object	1.Acts on an object that is rolling
2.Prevents an object from starting to move	2.Slows down a rolling object
3.It is generally greater	3.It is lesser than static friction

4. Write any three disadvantages of frictional force.

1. Friction causes wear and tear of machine parts, shoes, tyres, etc.
2. It produces heat which may damage machines or cause energy loss.
3. Friction reduces efficiency of moving parts, requiring more energy to work.

5. Why is frictional force called a necessary evil?

Friction is essential because it helps us walk, hold things, write, and drive vehicles.
At the same time, it has disadvantages like wear and tear, heat generation, and energy loss.
So, though it is troublesome, it is unavoidable and helpful in many ways.
That’s why friction is called a necessary evil – we need it but it also creates problems.

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💡 Exemplar Problems – Explained Answers

1. Cite a real-life example to justify that friction between two surfaces increases when they are pressed harder.

When you press a rubber eraser harder on paper and try to slide it, you’ll find it harder to move.
This is because greater force increases the contact between the surfaces, thus increasing friction.

2. Suggest a way to prevent the skidding of vehicles during rainy days.

Use tyres with deep grooves or tread patterns.
These grooves allow water to escape and maintain good grip between the tyres and road surface, preventing skidding.

3. Does a raindrop falling towards the Earth experience any force of friction?

Yes, the raindrop experiences air resistance, which is a type of fluid friction.
As the drop falls, it rubs against air particles, slowing it down slightly.

4. Think of one indoor sport and one outdoor sport of your choice. Discuss the role of frictional force in each case.

Indoor Sport – Table Tennis:
Friction between the ball and the paddle helps players control the spin and direction of the ball.
Outdoor Sport – Football:
Friction between the shoes (studs) and the ground prevents slipping and helps players run and stop quickly.

5. What will happen if frictional forces disappear?

We will not be able to walk, as our feet would slip.
Vehicles will not stop, even with brakes.
Writing will be impossible because the pen will slide on paper without leaving marks.
Machines will not function properly as their parts will keep slipping.