Question

(1) Friction is the force which resists the relative motion of surfaces
(ii) All types of surface like solid, liquid and air offer the force of friction.
(iii) Friction force always applies in the opposite direction of movement.
(iv) Friction is applied when two surfaces in contact move relative to each other.
Examples
(a) A moving wheel on the ground stops after covering a certain distance because surface of ground offers
opposite direction friction to the surface of wheel in motion,
(b) After applying breaks to a moving bike, the surface of brakes offers friction to the surface of moving
wheel and the bicycle stops because of force of friction.
(c) Gently push a book on a table. It stops after moving for some distance because of friction between the
surfaces of book and table.
Factors affecting Friction,
(0) Friction is caused by the irregularities on the two surfaces in contact.
(ii) Even those surfaces which appear very smooth but microscopic view show those irregularities. When
these surfaces come into contact, the irregularities of surfaces get interlocked. We have to apply force to
remove the interlocking, a surface produces friction when it slides or rolls over another surface.
(iii) Friction force will increase with increase in weight. As weight increases irregularities between surfaces
get interlocked tightly because of pressure, and the surface offers more resistance of friction.
Example: It is easier to dragging a mat when nobody is sitting on it than a person is sitting on it because of
friction increases with increase in weight.
(iv) Rougher surface offers more force of friction.
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Answer 1

Answer:

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