Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

1

(a)

Rolling, static, sliding

(b)

Rolling, sliding, static

(c)

Static, sliding, rolling

(d)

Sliding, static, rolling

It is difficult to walk on a wall polished floor because friction between our feet and floor is

1

(a)

increased

(b)

reduced

(c)

same

(d)

None of these

A toy car released with the same initial speed will travel farthest on

1

(a)

muddy surface

(b)

polished marble surface

(c)

cemented surface

(d)

brick surface

Rolling friction is smaller than

1

(a)

sliding friction

(b)

static friction

(c)

fluid friction

(d)

All of these

The fishes swim easily in the water because they have

1

(a)

more energy

(b)

streamlined shape

(c)

Both (a) and (b)

(d)

None of these

Friction opposes the  __________ between the surfaces in contact with each other.

1

(a)

relative motion

Sprinkling of powder on the carrom board ________ friction.

1

(a)

reduces

________ is produced by friction.

1

(a)

Heat

Friction can never be entirely __________

1

(a)

eliminated

The soles of our shoes get worn out after a period of time. It is due to ___________

1

(a)

friction

Static friction is greater than rolling friction.

1

(a) False

(b) True

Birds and fishes have streamlined shape.

1

(a) False

(b) True

Soapy floor is slippery due to less friction.

1

(a) False

(b) True

Fluid friction depends on the shape of an object placed in the fluid and nature of fluid.

1

(a) False

(b) True

Friction is harmful always.

1

(a) True

(b) False

Give an example which shows that friction can produce heat.

2

(a)

Rubbing of palms

Can we reduce friction to zero?

2

(a)

No, because no surface is perfectly smooth

List the parameters on which force of frictio depends.

2

(a)

1. Mention the moment when the rolling friction comes into play.

   2

   (a)

2. Why are oil, creams and grease called lubricants?

   2

   (a)

1. If there was no friction, then what would happen when an object starts moving?

   2

   (a)

2. Explain why sliding friction is less than the static friction.

   2

   (a)

1. Explain why a pencil will write on paper but not on glass.

   4

   (a)

2. Explain with the help of an example that heat is produced by friction.

   4

   (a)

Name any of the five smooth surfaces from your surroundings.

3

(a)

A marble is allowed to roll down an inclined plane from a fixed height. At the foot of the inclined plane, it moves on a horizontal surface (a) covered with silk cloth (b) covered with a layer of sand and (c) covered with a glass sheet. On which surface, will the marble move the shortest distance. Give reason for your answer.

3

(a)

Explain some examples where we have to reduce the friction.

5

(a)

Show with the help of an experiment that smoothness of surface reduces friction.

5

(a)