Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

1

(a)

wet marble floor, dry marble floor, newspaper, towel

(b)

newspaper, towel, dry marble floor, wet marble floor

(c)

towel, newspaper, dry marble floor, wet marble floor

(d)

Wet marble floor, dry marble floor, towel, newspaper

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

We can increase the friction by

1

(a)

polishing

(b)

making grooves and treads

(c)

streamlining

(d)

using ball bearing

If we apply oil on door hinges, the friction will

1

(a)

increase

(b)

decrease

(c)

disappear altogether

(d)

will remain unchanged

Ball bearings reduce friction because they rolls rather than ___________

1

(a)

slide

All objects moving in fluids have ________ shape to reduce friction.

1

(a)

streamlined

The substances are used in machines to protect their surfaces from wear and tear caused by ___________ are called lubricants.

1

(a)

friction

We pour a drop of oil on the hinge of door to __________ friction.

1

(a)

reduce

Friction can never be entirely __________

1

(a)

eliminated

Soapy floor is slippery due to less friction.

1

(a) False

(b) True

Friction increases with increase in smoothness of surface.

1

(a) True

(b) False

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

1

(a) False

(b) True

It is easy to roll the body over one another thanto slide it.

1

(a) False

(b) True

Friction is harmful always.

1

(a) True

(b) False

It is difficult to move on a wet marble floor. Why?

2

(a)

Give a reason for calling friction as a necessary evil.

2

(a)

The pieces of luggage fitted with the rollers. Explain why.

2

(a)

Is frictional force a contact force?

2

(a)

Why it is difficult to move on a wet marble floor?

2

(a)

You might have noticed that when used for a long time, slippers with rubber soles become slippery. Explain the reason.

3

(a)

Name any of the five smooth surfaces from your surroundings.

3

(a)

The handle of a cricket bat or a badminton racquet is usually rough. Explain the reason.

3

(a)

Two boys are riding their bicycles on the same concrete road. One has new tyres on his bicycle while the other has tyres that are old and used. Which of them is more likely to slip while moving through a patch of the road which has lubricating oil spilled over it?

3

(a)

While travelling on a rickshaw, you might have experienced that if the seat cover is very smooth, you tend to slip when brakes are applied suddenly. Explain.

3

(a)

Explain some examples where we have to reduce the friction.

5

(a)

Few days back, Shradha .a student of class VIIIth was driving the car. She went to a crop field. The level of road were just above the level of ploughed field. As she wanted to stop the slow-moving car, the brakes failed to work at that time. Suddenly, she turned the car towards the ploughed field. After sometime, the car came to rest.
(a) Shradha turned the car towards the ploughed field. Explain why.
(b) Explain, how the car came to rest after covering some distance in the ploughed field.
(c) Mention the values that Shradha exhibits here.

5

(a)