Friction

Discussion

The force between surfaces in contact that resists their relative tangential motion (slipping).

Types: static & kinetic

Classical Approximations

ƒ = μN

microscopic description

miscellaneous stuff

μs μk interface 
  1.16 rubber rubber
  1.02 rubber concrete
  0.72 car tire asphalt
  0.35 car tire grass
0.8–1.0   skin metals
0.9–1.0   glass glass
  0.9 sheep steel mesh
  0.7 sheep plastic batten (⊥)
  0.6 sheep plastic batten (∥)
  0.6 sheep wood batten (⊥)
  0.5 sheep wood batten (∥)
0.60–0.70   masonry brick
0.68   horseshoe rubber
0.58   horseshoe concrete
0.58   steel steel
0.4   brakes cast iron
0.62   wood concrete
0.6   wood brick
0.2–0.4   wood stone
0.2–0.6   wood metals
0.29 0.22 wood felt
0.28 0.17 wood wood
0.56   leather metals
0.27–0.38   leather oak
0.3   snow nylon
0.04–0.4 0.04–0.4 snow hickory, waxed
0.1   graphite graphite
0.1   graphite steel
  0.03 ice steel
0.05–0.5 0.02–0.09 ice ice
0.2   teflon steel
0.04   teflon teflon
  0.0044–0.0057 ankle cartillage synovial fluid
  0.0013 tendon sheath
Coefficients of Friction for Selected Interfaces
(in order of generally decreasing value)