Page 1 - lesson notes -Types of friction

SAI INTERNATIONAL SCHOOL
Class8
Lesson Notes
Subject-Physics
CH-Friction
Subtopic-Types of Friction

Types of Friction
There are three types of friction that exist between solid surfaces. They are
1) static friction,
2) sliding friction and
3) rolling friction.

STATIC FRICTION: Frictional force that comes into action before the start of the
motion of an object is called static friction. Example: We tried to push a box placed
on the floor but not able to move it.

1) Maximum value of static friction is called limiting friction.
2) Acts when an object is stationary.
3) Must be overcome to initiate motion.
4) Self-adjusting up to a maximum limit (limiting friction).

Examples:
• A book resting on a table.
• A ladder leaning against a wall.

SLIDING FRICTION: When an object slides over another surface, the frictional force
that comes into action is sliding friction. Example: a boy sliding on a slide.
1) Sliding friction is smaller than limiting friction.
2) Acts when an object is in motion.
3) It is because irregularities do not get time to interlock properly when one
surface is sliding over the other.
Examples:
• Pushing a box across the floor.
• Applying brake, a bicycle to a stop.

ROLLING FRICTION: The frictional force exerted when an object rolls over a
surface is called rolling friction. Example: rolling ball on the ground.
1) Rolling friction has the minimum value.
2) Enables smooth motion of wheels and balls.
3) Wheels or rollers are used to reduce friction significantly.

Examples:
• A ball rolling on the ground.
• Wheels of a moving car.