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Friction - Important Questions Model Paper In 8th Science

Published on: 02/08/2018

In Friction contains important questions in CBSE 8th Standard Science. It also covered with the most important questions in Friction.
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Questions:

Multiple Choice Question

10 x 1 = 10

A boy rolls a rubber ball on a wooden surface. The ball travels a short distance before coming to rest. To make the same, ball travel longer distance before coming to rest, he may

(a)

spread a carpet on the wooden surface

(b)

cover the ball with a piece of cloth

(c)

sprinkle talcum powder on the wooden surface

(d)

sprinkle sand on the wooden surface

Rolling friction is smaller than

(a)

sliding friction

(b)

static friction

(c)

fluid friction

(d)

All of these

Fine powder is poured on the carromboard to

(a)

increase friction

(b)

decrease friction

(c)

Both (a) and (b)

(d)

None of these

If we apply oil on door hinges, the friction will

(a)

increase

(b)

decrease

(c)

disappear altogether

(d)

will remain unchanged

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

(a)

increased

(b)

reduced

(c)

same

(d)

None of these

Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play

(a)

only if the objects are solid

(b)

only if one of the two objects is liquid

(c)

only if one of the two objects is gaseous

(d)

irrespective of whether the objects are solids, liquids or gases

Friction is due to

(a)

polishing of surface

(b)

streamlining of body

(c)

interlocking of irregularities

(d)

None of the above

The force of friction always

(a)

opposes motion

(b)

helps the motion

(c)

Both of these

(d)

None of the above

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

(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

10.

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.

(a)

Rolling, static, sliding

(b)

Rolling, sliding, static

(c)

Static, sliding, rolling

(d)

Sliding, static, rolling

Generic 3

5 x 3 = 15

11.

Name any of the five smooth surfaces from your surroundings.

12.

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

13.

Give examples to show that friction is both a friend and a foe.

14.

You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?

15.

Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Generic 2

5 x 2 = 10

16.

Can we eliminate friction completely?

17.

Why are oil, creams and grease called lubricants?

18.

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

19.

Is frictional force a contact force?

20.

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

Generic 5

2 x 5 = 10

21.

In physics classroom a teacher told to his students that when a cricket player want to catch a ball then first he rub the hands. Thus, there is less chance of slipping the ball from hands.
(a) Explain the reason of not slipping of ball from hand
(b) If the player makes his hands oily instead of rubbing them. Would he be able to catch the ball?
(c) Mention the type of teaching skills of teacher is being represented here?

22.

We have two identical metal sheets. One of them is rubbed with sand paper and the other with ordinary paper. The one rubbed with sand paper shines more than the other. Give reason.

Fill up / 1 Marks

5 x 1 = 5

23.

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

24.

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

25.

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

26.

Ball bearings reduce friction because they rolls rather than ___________

27.

Static friction is ________ than the sliding friction.

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Answers Key:

Multiple Choice Question

10 x 1 = 10

(d)
All of these

(b)
decrease friction

(b)
decrease

(b)
reduced

(d)
irrespective of whether the objects are solids, liquids or gases

(a)
opposes motion

The correct arrangement is as follows: Wet marble floor, dry marble floor, newspaper, towel.

10.

Generic 3

5 x 3 = 15

11.

The five smooth surfaces are
(i) Glazed tiles
(ii) Surface of an oily plot
(iii) Surfaces of wet soaps
(iv) Mirror surface
(v) Floor of polished room

12.

It is due to continuous rubbing of soles with the ground, the spikes on the sole get damaged slowly and the soles become Slippery.

13.

Friction as a friend
(i) It allows us to walk comfortably.
(ii) It allows us to minimise the speed or to stop the moving objects.
(iii) It allows us to write on a board with chalk.
Friction as a foe
(i) It causes wear and tear in objects.
(ii) It causes damage to the parts of machines.
(iii) It does not allow the free movement of objects.

14.

After spilling a bucket of soapy water on a marble floor, it would be more difficult for us to walk on the floor. Because the layer of soapy water reduces the friction and the foot cannot make a proper grip on the floor.

15.

A book kept on tilted writing desk starts sliding down. The direction of frictional force is in the opposite direction. Thus, frictional force will act in upward direction.

Generic 2

5 x 2 = 10

16.

No, we cannot eliminate friction completely because it is the characteristic property (molecular property) of material.

17.

Oil, creams and grease when applied on a surface make it smooth, thus reduce friction, so these are called lubricants.

18.

On a wet marble, floor, frictional force between the foot and floor decreases making it slippery, thus we feel difficult to move on a wet marble floor.

19.

Yes, because friction acts only when two surfaces are in contact with each other.

20.

In order to reduce single friction, pieces of luggage are fitted with rollers so that even a child can pull the luggage easily.

Generic 5

2 x 5 = 10

21.

(a) Since, the player rub his hand due to which the palms become warm which absorb the moisture from the surface and make the surface rough. So, due to roughness of hands, the ball may get a better grip between the hands and does not slip.
(b) Since, the player makes the palm surface oily. So, the number of irregularities decreases and the surface becomes smooth. So, the ball slips off easily from the hand.
(c) As, teacher wants to teach the students through easy example. So, this act of teacher shows the experience and ideality of teacher.

22.

While rubbing with sand paper, more frictional force is produced between the layers of metal sheet and sand paper which causes more force on dust particles and they are removed easily, so it will shine more. But in case of ordinary paper, the force of friction is not sufficient to remove all the dust, so it will shine less in this case.

Fill up / 1 Marks

5 x 1 = 5

23.