II. SHORT ANSWER TYPE QUESTIONS

1. A ball rolled on the ground stops after some time. Why? Name the force responsible for it.

• The ball stops because of friction between the ball and the ground.
• Friction opposes motion and gradually reduces the speed until it stops.

2. Can we walk on a frictionless floor? Give reason.

• No, we cannot walk on a frictionless floor.
• Walking needs friction between our feet and the ground to push backward and move forward. Without friction, our feet would just slip.

3. Give reason for the following:
(a) Luggage trolley has wheels.

• Wheels reduce friction, making it easier to pull or push heavy luggage.

(b) Aeroplanes have streamlined shape.

• Streamlined shape reduces air resistance (drag), allowing airplanes to move faster and more smoothly.

III. LONG ANSWER TYPE QUESTIONS

1. Give two examples showing that friction is necessary in everyday life.

• We are able to walk because friction gives grip to our feet.
• Vehicles can move on the road due to friction between tyres and the road.

2. Give two examples showing the harmful effects of friction.

• Friction causes wear and tear of machine parts and tyres.
• Friction produces unwanted heat in machines, wasting energy.

3. Mention two simple methods for reducing friction.

• Applying lubricants like oil or grease between moving parts.
• Using ball bearings to reduce contact between surfaces.

4. Give reason for the following:
(a) Driving on an icy road is dangerous.

• Because ice reduces friction, tyres cannot grip the road properly, causing vehicles to slip.

(b) Why is machine oil poured on the moving parts of a machine?

• Oil reduces friction and wear, helping parts move smoothly and last longer.

(c) Why do we generally sprinkle a little talcum powder on a carrom board?

• Powder reduces friction between the striker/coins and the board, so they slide easily.

5. Describe various types of friction.

• Static friction: The friction that prevents an object from starting to move.
• Sliding friction: The friction when two surfaces slide over each other.
• Rolling friction: The friction when an object rolls on a surface (less than sliding friction).
• Fluid friction: Friction experienced when an object moves through air or liquid.

IV. HIGHER ORDER THINKING SKILLS

1. Why most forms of land transportation use wheels?

• Wheels convert sliding friction into rolling friction, which is much less.
• This makes movement smoother, faster, and requires less energy.

2. During rainy season sand is spread on wet slippery roads or when it snows. Why?

• Wet roads or snow have very low friction.
• Sand increases roughness, improving grip for tyres and preventing slipping.