Friction and Friction Coefficients of some Common Materials

Friction theory and friction coefficients for some common materials and materials combinations

Sponsored Links

Frictional force can be expressed as

F_f = μ N (1)

where

F_f = frictional force (N, lb)

μ = static (μ_s) or kinetic (μ_k) frictional coefficient

N = normal force (N, lb)

For an object pulled or pushed horizontally, the normal force - N - is simply the weight:

N = m g (2)

where

m = mass of the object (kg, slugs)

g = acceleration of gravity (9.81 m/s², 32 ft/s²)

Frictional Coefficients for some Common Materials and Materials Combinations

Materials and Material Combinations		Static Frictional Coefficient - μs
		Clean and Dry Surfaces	Lubricated and Greasy Surfaces
Aluminum	Aluminum	1.05 - 1.35	0.3
Aluminum-bronze	Steel	0.45
Aluminum	Mild Steel	0.61
Brake material	Cast iron	0.4
Brake material	Cast iron (wet)	0.2
Brass	Steel	0.35	0.19
Brass	Cast Iron	0.31)
Brick	Wood	0.6
Bronze	Steel		0.16
Bronze	Cast Iron	0.221)
Bronze - sintered	Steel		0.13
Cadmium	Cadmium	0.5	0.05
Cadmium	Mild Steel	0.461)
Cast Iron	Cast Iron	1.1, 0.151)	0.071)
Cast Iron	Oak	0.491)	0.0751
Cast iron	Mild Steel	0.4, 0.231)	0.21, 0.1331)
Carbon (hard)	Carbon	0.16	0.12 - 0.14
Carbon	Steel	0.14	0.11 - 0.14
Chromium	Chromium	0.41	0.34
Copper-Lead alloy	Steel	0.22
Copper	Copper	1	0.08
Copper	Cast Iron	1.05, 0.291)
Copper	Mild Steel	0.53, 0.361)	0.181)
Diamond	Diamond	0.1	0.05 - 0.1
Diamond	Metal	0.1 - 0.15	0.1
Glass	Glass	0.9 - 1.0, 0.41)	0.1 - 0.6, 0.09-0.121)
Glass	Metal	0.5 - 0.7	0.2 - 0.3
Glass	Nickel	0.78	0.56
Graphite	Steel	0.1	0.1
Graphite	Graphite (in vacuum)	0.5 - 0.8
Graphite	Graphite	0.1	0.1
Iron	Iron	1.0	0.15 - 0.20
Lead	Cast Iron	0.431)
Leather	Oak	0.61, 0521
Leather	Metal	0.4	0.2
Leather	Wood	0.3 - 0.4
Leather	Clean Metal	0.6
Magnesium	Magnesium	0.6	0.08
Nickel	Nickel	0.7 - 1.1, 0.531)	0.28, 0.121)
Nickel	Mild Steel	0.641)	0.1781)
Nylon	Nylon	0.15 - 0.25
Oak	Oak (parallel grain)	0.62, 0.481)
Oak	Oak (cross grain)	0.54, 0.321	0.0721
Phosphor-bronze	Steel	0.35
Platinum	Platinum	1.2	0.25
Plexiglas	Plexiglas	0.8	0.8
Plexiglas	Steel	0.4-0.5	0.4 - 0.5
Polystyrene	Polystyrene	0.5	0.5
Polystyrene	Steel	0.3-0.35	0.3 - 0.35
Polythene	Steel	0.2	0.2
Polystyrene	Polystyrene	0.5	0.5
Rubber	Dry Asphalt	0.5 - 0.81)
Rubber	Wet Asphalt	0.25 - 0.751)
Rubber	Dry Concrete	0.6 - 0.851)
Rubber	Wet Concrete	0.45 - 0.751)
Silver	Silver	1.4	0.55
Sapphire	Sapphire	0.2	0.2
Silver	Silver	1.4	0.55
Steel	Steel	0.8	0.16
Teflon	Teflon	0.04	0.04, 0.041)
Teflon	Steel	0.04	0.04
Tungsten Carbide	Steel	0.4-0.6	0.1 - 0.2
Tungsten Carbide	Tungsten Carbide	0.2 - 0.25	0.12
Tungsten Carbide	Copper	0.35
Tungsten Carbide	Iron	0.8
Teflon	Teflon	0.04	0.04
Tin	Cast Iron	0.321)
Wood	Clean Wood	0.25 - 0.5
Wood	Wet Wood	0.2
Wood	Clean Metal	0.2 - 0.6
Wood	Wet Metals	0.2
Wood	Concrete	0.62
Wood	Brick	0.6
	Wet snow	0.14, 0.11)
Wood - waxed	Dry snow	0.041)
Zinc	Cast Iron	0.85, 0.211)
Zinc	Zinc	0.6	0.04

¹⁾ Kinetic frictional coefficient

Kinetic versus Static Frictional Coefficients

Kinetic frictional coefficients are used with relative motion between objects. Static frictional coefficients are used for objects without relative motion. Static coefficients are somewhat higher than kinetic coefficients.

Example - Friction Force

The friction force of a 100 lb wooden crate pushed across a concrete floor with friction coefficient of 0.62 can be calculated as:

F_f = 0.62 100 (lb)

= 62 (lb)

·         1 lb = 0.4536 kg