Kinetic Friction (College Board AP® Physics 1: Algebra-Based)

Kinetic friction

• When two surfaces are in contact with each other, each surface exerts a contact force on the other

  • The component of the contact force parallel to the contact surface is called friction

• Friction between two solid surfaces is caused by imperfections in the contact surfaces of the objects moving or attempting to move over one another

Imperfections

• There are two forms of friction:

  • kinetic friction

  • static friction

Kinetic friction

• Kinetic friction occurs when two surfaces in contact move relative to each other

  • The word kinetic means movement or motion

• The kinetic friction force is exerted in a direction opposite to the motion of each surface relative to the other surface

Components of friction

• Kinetic friction between two surfaces in contact when one surface moves over the other:

  • decreases the speed of the moving surface

  • increases the temperature of the contact surfaces due to heating 

• The force of friction between two surfaces does not depend on the size of the surface area of contact

  • The magnitude of the force of friction is determined by the nature of the surfaces in contact and the normal reaction force acting between them