EVENTS CONVENT HIGH SCHOOL
27/11/2021 CLASS- 8 SESSION 2021-22
SUBJECT : SCIENCE
CHAPTER-12
FRICTION
______________________________________
Question 1.Fill in the blanks.
(a) Friction opposes the ______ between the surfaces in contact with each other.
(b) Friction depends on the ______ of surfaces.
(c) Friction produces ______
(d) The sprinkling of powder on the carrom board _______ friction.
(e) Sliding friction is _______ than the static friction.
Solution:
(a) relative motion
(b) smoothness (or irregularities or nature)
(c) heat
(d) reduces
(e) less
Question .2 Very Short Questions and Answers
Question 1.
Define friction.
Answer:
Friction is the force which resists the motion of a body, while moving on a surface.
Question 2.
What is meant by sliding friction ?
Answer:
When one surface is sliding over the other, sliding friction comes into play.
Question 3.
When does static friction come into play ?
Answer:
Static friction comes into play to counter balance the applied force on the body.
Question 4.
What are lubricants ?
Answer:
The substances which reduce friction are called lubricants.
Question 5.
What is rolling friction ?
Answer:
When one body rolls over the surface of another body, the resistance to its motion is called the rolling friction.
Question 6.
What are fluids ?
Answer:
Fluids is the common name given to gases and liquids.
Question 7.
Do fluids exert friction ?
Answer:
Yes, fluids also exert friction.
Question 8.
What is meant by air resistance ?
Answer:
There is friction between a moving object and the air through which it moves, known as air resistance.
Question .3 Short Questions and Answers
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.
