Page 63 - Physics - XI

5. The weights in the pan should be placed gently and carefully.
6. The weights in the pan should be increased in small steps.

Sources of Error
1. The pulley may not be frictionless.
2. The glass plate may not be exactly horizontal.

3. Weights may not be standard.
VIVA VOCE

Q1. What is friction?
Ans. The opposing force which comes into play when a body slides or rolls over the surface of another
body is called force of friction. It acts in the direction opposite to the direction of motion of the body.

Q2. What is limiting friction?
Ans. Limiting friction is the maximum value of the opposing force which comes into play when one body
is just at the verge of moving over the surface of another body.

Q3. Defi ne coeffi cient of limiting friction.
Ans. It is the ratio between force of limiting friction (F ) to the normal reaction (R) between the surfaces
L
in contact.

F L
L
R
µ is the coeffi cient of limiting friction.
L
Q4. What is the cause of friction?
Ans. The force of friction arises on account of strong atomic or molecular forces of attraction between
the two surfaces at the points of actual contact.
Q5. Does static friction depends upon the applied force?

Ans. The static friction is a self adjusting force. It increases with the applied force till the body just starts
moving on a surface.

Q6. Defi ne rolling friction.

Ans. The force of friction which comes into play when a body rolls over the surface of another body is
called rolling friction.

Q7. What is dynamic friction?
Ans. It is the opposing force that comes into play when one body is actually moving over the surface of
another body.

Q8. What are the factors upon which limiting friction depends?
Ans. It depends upon the normal reaction and the nature of the two surfaces in contact.

Q9. On what factors does the coeffi cient of limiting friction (µ ) depend?
L
Ans. The value of μ depends upon the nature of the two surfaces in contact and the condition of the
L
surfaces.

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