CBSE Class 8, NCERT Science
Chapter 12, FRICTION
CBSE Notes - CBSE Guide - Solutions of CBSE Sample Questions
Keep in Mind
=> Friction is the force equal and opposite to the relative
motion between the two surfaces in contact.
=> Friction has no relation with area of contact (exposed to
the force of friction).
=> Sliding friction is less than the static friction.
=> Friction is a necessary evil.
Definitions / Terms
Static Friction
Static Friction is the friction which is produced between two
surfaces in contact with each other at the position of rest. This friction is
more powerful than any other type of friction. It is most difficult to overcome
the static friction because at this position, the irregularities are most
effectively pressed against each other. This type of friction needs a lot of
energy to overcome.
Sliding Friction
This type of friction arises when two objects in contact are in
motion. It is lesser than Static friction. This friction is lesser because the
irregularities of both surfaces do not get enough time to get locked with each
other as the objects are already in motion.
Rolling Friction
Rolling friction is the friction which comes in effect when two
bodies are rolling on each other. Rolling movement of both objects don’t allow
the locking of irregularities, thus it is the smallest force (friction) of all
the three types.
Drag
It is the term used to describe the frictional force which is
exerted by the fluids on the bodies moving in it. This friction needs a lot of
energy to overcome so, bodies of such objects which move in fluids are
streamlined to counter the friction offered by fluids.
Solutions
of CBSE Sample Questions
Question.1: Fill in the blanks:
1) Friction
always works in _____ direction of motion of the surface.
2) Friction
depends on the relative ______ between two surfaces.
3) _______
is also produced with friction.
4) Shape
of the objects moving in the fluid is _____ to overcome friction exerted by the
liquids.
5) _______
are used in machines to protect their surfaces from wear due to friction.
6) Soapy
floor is slippery due to ______ friction.
7) Ball
bearings are used to convert static friction into _______ friction.
8) Sliding
friction is ______ than the static friction.
9) Friction
increases with the increase in _______.
10) _____
type of friction is the most powerful among all types of frictions.
Question.2: What causes friction between two
surfaces?
Question.3: In which direction does friction
work?
Question.4: What is done to tires of the
vehicles to reduce the friction?
Question.5: What does friction produce?
Question.6: Name any machine where ball
bearing is used to reduce friction.
Question.7: What are the factors of friction?
Question.8: Can we eliminate friction
completely?
Question.9:
What causes chalk to write on the black-board?
Question.10:
How does the nature of surface effect friction?
Question.11:
It is easy to move an object on a sliding surface (inclined surface) than on a
plane surface. Why?
Question.12:
Why is it difficult to move an object from its static position?
Question.13: Why friction is called a necessary
evil ?
Question.14: Why do we need to decrease
friction?
Question.15: Explain the different types of
friction.
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