• The frictional force between two stationary surfaces is called the static friction,  f_s.
• The frictional force between two sliding surfaces is called the kinetic friction, f_k.

• It can be shown empirically that between two particular surfaces
  • static friction f_s ranges from zero to a maximum value.

0 < f_s < μ_sN

• • kinetic friction f_k is constant and independent of speed.

f_k = μ_kN 

• • maximum static friction is larger than kinetic friction.
• Even though there are exceptions, friction (both static and kinetic) is usually not dependent on the area of contact.

• 03 Dynamics