1.What is Friction?

Friction is a force that opposes motion between two surfaces that are in contact.
Whenever an object moves or tries to move over another surface, friction acts in the opposite direction of motion.

Example:

  • A ball slows down when rolled on the ground.

  • Rubbing hands together produces heat.

2. When Does Friction Occur?

Friction occurs when:

  • Two surfaces touch each other, and

  • One surface moves or tries to move against the other.

Friction does not act when there is no contact between surfaces.

Examples:

  • Sliding a book on a table

  • Walking (your foot and the ground create friction)

  • A tyre rolling on the road

3. Friction as a Contact Force

Friction is called a contact force because it acts only when surfaces are in physical contact.
It arises due to irregularities (tiny bumps) present on all surfaces.
These irregularities interlock when surfaces touch, causing friction.

Key idea:
More roughness → More friction
More smoothness → Less friction

PreviousNext