a. While playing carrom we sprinkle boric powder on the carrom board for
i. make the surface shine
ii. reduce the friction
iii. make the surface rough
iv. increase the friction

Answer: ii. reduce the friction

b. Which of the following is true for friction?
i. Stops a moving object
ii. Changes the shape of an object
iii. Changes the direction of a moving object
iv. Makes a moving object move faster

Answer: i. Stops a moving object

c. We can increase friction by:
i. making the surface smooth
ii. making grooves
iii. applying powder
iv. lubricating

Answer: ii. making grooves

d. Which of the following is correct for a streamlined body?
i. Increases friction
ii. Increases weight
iii. Reduces friction
iv. Reduces weight

Answer: iii. Reduces friction

2. Assertion and Reasoning

(A) In the following questions, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) below:

a. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
b. Both Assertion (A) and Reason (R) are true, and Reason (R) is not the correct explanation of the Assertion (A).
c. Assertion (A) is true, but Reason (R) is false.
d. Assertion (A) is false, but Reason (R) is true.

i. Assertion (A): A heavy bag can be easily pulled on rollers.
Reason (R): Rolling friction is weaker than sliding friction.

Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

ii. Assertion (A): If the sole of the shoe is worn out then we can slip easily.
Reason (R): The friction on a smooth surface is less than the friction on a rough surface.

Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

3. Answer the following questions in one sentence.

a. What is the unit for friction?

• The unit of force, and therefore friction, is the newton (N).

b. How does streamlining reduce friction?

• Streamlining reduces friction by shaping an object to allow fluids (air or water) to flow around it smoothly, minimizing resistance or drag.

c. Define the force of friction.

• Friction is a force that opposes the relative motion between two surfaces that are in contact with each other.

d. What is drag?

• Drag is the frictional force exerted by a fluid (like air or water) on an object moving through it.

4. Answer the following questions in 2-3 sentences.

a. Why are the tyres of vehicles grooved?

Answer. The grooves on tyres are called treads. They are designed to increase friction by providing a better grip on the road surface, which prevents skidding and slipping, especially on wet or muddy roads.

b. What are the two factors on which the force of friction depends?

Answer. The force of friction primarily depends on: (1) The nature of the surfaces in contact (rough or smooth). 2) The force pressing the surfaces together (normal force).

c. Why do athletes use shoes with spikes?

• Athletes use spiked shoes to dramatically increase friction between their shoes and the ground. The spikes dig into the track, providing a superior grip that prevents slipping and allows for a powerful push-off during running or jumping.

d. Arrange the different types of friction in ascending order. Explain your arrangement with the help of an example.

• The types of friction in ascending order (from weakest to strongest) are: Rolling < Sliding < Static.
• For example, a heavy box is hardest to start moving (static friction). Once moving, it’s easier to keep sliding (sliding friction). Easiest of all is to pull it on a cart with wheels (rolling friction).

5. Answer the following questions in 3-4 sentences.

a. What are the three factors on which the fluid friction depends?

• Fluid friction, or drag, depends on three main factors:
• The speed of the object: Friction increases with speed.The shape of the object: Streamlined shapes face less friction.
• The nature of the fluid: Thicker (more viscous) fluids like honey offer more friction than thinner fluids like water or air.

b. Explain the disadvantages of friction.

• Friction has several disadvantages: it causes the wearing and tearing of surfaces like soles of shoes or machine parts. It also generates heat, which can damage engines, and it opposes motion, meaning more force (and thus more energy/fuel) is required to move objects.

c. List two ways to increase friction with examples.

Two ways to increase friction are:

Making surfaces rougher: For example, adding treads to tyres or putting gravel on a slippery road.

Increasing the force pressing the surfaces together: For example, a heavier object experiences more friction than a lighter one on the same surface.

d. What is streamlining and why are ships and boats given streamlined shapes?

Streamlining is the process of designing an object with a narrow, tapered front and a sloping back to allow a fluid to flow around it easily. Ships and boats are given streamlined shapes to reduce water resistance (drag). This allows them to move through water more smoothly, using less fuel and achieving higher speeds.