Rolling and Using Treads to Change Friction

Q.

What is the purpose of using ball bearings in machines?

Q.

Question 1
Give two examples each of situations in which you push or pull to change the state of motion of objects.

Q.

Ball bearing is a device which usually converts:
(a) rolling friction into sliding friction
(b) static friction into sliding friction
(c) sliding friction into rolling friction
(d) rolling friction into static friction

Q.

Why does a bowler rub the cricket ball on his clothes before his cricket match?

Q.

Why are treads made on the surface of tyres?

Q.

Name any two machines in which ball bearings are used.

Q.

Name the device which is used between the hubs and axles of bicycle wheels to reduce friction.

Q.

Name the device which is attached to heavy luggage (such as a heavy suitcase) to move it easily by pulling.

Q.

State one way in which the friction between wheel and its axle can be reduced.

Q. Slick tyres offer far more grip as compared to treaded tyres on dry surfaces.

1. False
2. True

Q.

Why are the tyres with worn out surface replaced?

Q.

Different types of shoes are worn to walk on melting ice. The soles of these shoes should have

1. smooth surface

2. no grooves

3. spikes.

4. powder

Q.

Why F1 cars have smooth tyres?(30 words)

Q.

Friction in moving parts of a machine can be reduced by using ___________.

1. lubricants

2. ball bearings

3. iron filings

4. Both (A) and (B).

Q. Treads help expel water out of the way so that tyres can grip well on wet roads.

1. True
2. False

Q.

Friction in a moving parts of a machine can be reduced by using ___________.

Q. Why is having treads on tyres undesirable for racing cars (like the Formula1 cars)?

1. Friction would increase as treads increase friction and thus, tyres would start skidding.
2. Friction would reduce as tyres cannot take advantage of the plowing effect on hard roads if they have treads.
3. Friction would reduce because treads would make F1 tyres smaller.
4. Friction would increase as treads increase surface irregularities.

Q.

Force of friction is a disadvantage in moving vehicles on the road.

1. True
2. False

Q. Why is pulling easier than pushing ?

Q. F1 cars don't have treaded tyres and hence cannot develop sufficient friction.

1. False
2. True

Q. A block is placed on a rough surface. John is pushing the block with a force of 20 N, while Rob is pushing it with a force of 10 N. If the block does not move, calculate the frictional force acting on it.

1. 5 N
2. 10 N
3. 15 N
4. 20 N

Q.

Friction cannot be reduced.

1. True
2. False

Q.

Name the forces demonstrated by the following:

The slow movement of ball bearings through a tall jar of oil.

Q. Treaded tyres help in improving grip while moving on soft surfaces.

1. False
2. True

Q. Statement 1: Wrestlers apply oil on their bodies to increase friction.
Statement 2: Grooving provides a better grip.
Choose the correct option.

1. Only statement 2 is correct.
2. Both statements are incorrect.
3. Both statements are correct.
4. Only statement 1 is correct.

Q. A wooden block is lying on a horizontal table. A 2 N force is applied to the block in horizontal direction, and still the block remains at rest. What is the force of friction offered by the table?

1. 1.8 N
2. 2 N
3. 2.2 N
4. 0 N

Q.

Mention three methods of reducing friction in a machine.

Q. Treaded tyres help in improving grip while moving on soft surfaces.

1. False
2. True

Q. A block is placed on a rough surface. John is pushing the block with a force of 20 N, while Rob is pushing it with a force of 10 N. If the block does not move, calculate the frictional force acting on it.

1. 5 N
2. 10 N
3. 15 N
4. 20 N

Q. Why is having treads on tyres undesirable for racing cars (like the Formula1 cars)?

1. Treads increase friction and hence tyres start skidding
2. Tyres cannot take advantage of the plowing effect on hard roads if they have treads and hence friction will reduce
3. Friction would reduce because treads would make F1 tyres smaller
4. None of the above