Wed. Jul 6th, 2022

2 Mark Questions for NCERT Solutions for Class 8 Science Chapter 12

Question 1.
When your writing desk is tilted a little, a book kept on it starts sliding down. Mention the direction of the frictional force acting on it.
Answer:
The frictional force acts in the upward direction.

Question 2.
You spill a bucket of soapy water on a marble floor accidently. Would it make easier or more difficult for you to walk on the floor ? Why ? [NCERT]
Answer:
It would be more difficult to walk on the floor with soapy water because when we walk on a soapy floor, there is little friction between the floor and the feet, so it becomes difficult to walk.

Question 3.
Put a tick mark on the correct choice :
When one object moves over the surface of other object.

  • surface of only lower object exerts frictional force on the upper object.
  • surface of only upper object exerts frictional force on the lower object.
  • surfaces of both the objects exert force on each other.
  • surfaces of both the objects exert force in a direction opposite to each other.

Answer:
Surfaces of both the objects exert force in a direction opposite to each other.

Question 4.
Four children have got similar toy cars. They run the car on the dry marble floor, wet marble floor, newspaper and towel simultaneously. The force of friction between the car and different surfaces in increasing order will be :

  • Wet marble floor, dry marble floor, newspaper and towel.
  • Newspaper, towel, dry marble floor, wet marble floor.
  • Towel, newspaper, dry marble floor, wet marble floor.
  • Dry marble floor, wet marble floor, towel, newspaper.

Answer:
Wet marble floor, dry marble floor, newspaper and towel.

Question 5.
Explain why sportsmen use shoes with spikes. [NCERT]
Answer:
Sportsman use shoes with spikes to increase the friction. In this way, the sportsman can run faster.

Question 6.
Iqbal has to push a lighter box and Seema has to push a similar heavier box on the Who will have to apply a larger force and why ? [NCERT]
Answer:
Seema will have to apply more force because the weight of the box increase and the friction increases. For a heavier box the ridges of the surfaces get interlocked more.

Question 7.
Explain why sliding friction is less than static friction. [NCERT]
Answer:
Sliding friction is less than static friction because it comes into play once the body has started sliding. To make the body slide, more force is required to overcome the irregularities in the surface of the body.

Question 8.
Explain why objects moving in fluids must have special shapes. [NCERT]
Answer:
Fluids also exert a frictional force on the body moving through them. Therefore, the shape of the body is streamlined to over the frictional force of fluids and to move smoothly through them.

Question 9.
Why does the force of friction exist ?
Answer:
Friction is caused by the irregularities on the two surfaces in contact.

Question 10.
Can we have surfaces with zero friction ?
Answer:
No, the friction can be less in some surfaces, but it can never be zero.

Question 11.
Which surface have more friction – rough or smooth ? Why ?
Answer:
Rough surfaces have more friction because they have larger number of irregularities.

Question 12.
Why is it possible to write on rough blackboard with chalk ?
Answer:
The chalk is rubbed on the rough blackboard while writing. In the process soft chalk particles get stuck to the irregularities of rough blackboard susfare making the writing visible.

Question 13.
A ball is set rolling on the ground. Will it stop by itself ? Why ?
Answer:
The ball will stop after sometime because the force of friction is acting from the opposite direction.

Question 14.
Why do the soles of shoes wear out ?
Answer:
The soles of shoes wear out due to the friction between the soles and the ground.

Question 15.
Why are the soles of shoes grooved ?
Answer:
Soles of shoes are grooved so as to provide better grip between the shoes and the ground.

Question 16.
Give two examples where rolling friction is utilized.
Answer:
Rolling friction is utilized by using ball bearings between the hub and the axle of a ceiling fan and the bicycle.

Question 17.
What is function of ridges on your palm and bottom of your feet ?
Answer:
The function of the ridges is to increase the friction.

Question 18.
Name the two factors on which the magnitude of frictional force depends.
Answer:
Frictional force depends on

  • The weight of the body and
  • The nature of the surface in contact.

Question 19.
Give two methods by which friction is reduced in the wheels of the car.
Answer:

  • The wheels of the car are provided with ball bearings along the axle which reduce the friction.
  • The tube and tyres are inflated which reduce friction.

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