Friction

Science

Definition

A contact force that opposes the relative motion or tendency of motion between two surfaces. Static friction prevents motion from starting, while kinetic friction acts on objects already sliding. Friction depends on the surfaces involved and the normal force.

Examples

  • Brake pads using friction to slow a car's wheels
  • Rubber shoe soles providing grip on a wet floor
  • Sandpaper using friction to smooth wood surfaces
Key Fact

f = μN, where μ is the coefficient of friction and N is the normal force

Related Terms

Free-body diagrams Net force Newton's three laws Work

Study This Concept

Practice friction with free review games in these units:

AP Physics 1 Unit 2: Forces and Newton's Laws Physics Unit 2: Forces and Newton's Laws