Coefficient of kinetic friction

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Template:Constitutive coefficient

Definition

Given two surfaces, the coefficient of kinetic friction or coefficient of dynamic friction between them is the constant \mu_k such that, for small speeds of slipping of two bodies with these two as the surfaces of contact, the kinetic friction between the two bodies is \mu_k times the normal force between the two bodies.

The coefficient of kinetic friction is usually slightly, but not much, smaller than the limiting coefficient of static friction.

Units and dimensions

The coefficient of kinetic friction is a dimensionless scalar and does not need units.

Range of values

First surface Second surface Condition \mu_s \mu_k \tan^{-1}(\mu_s) (radians) \tan^{-1}(
\mu_s) (degrees) \tan^{-1}(\mu_k) (radians) \tan^{-1}(\mu_k) (degrees)
Aluminimum Mild steel Dry and clean 0.61 0.47 0.55 31 0.44 25
Aluminimum Aluminimum Dry and clean 1.05 - 1.35 1.4 0.81 - 0.93 46 - 53 0.95 54
Copper Steel Dry and clean 0.53 0.36 0.49 28 0.35 20
Copper Copper Dry and clean 1.0  ? 0.79 45  ?  ?
Wood Concrete Dry and clean 0.62  ? 0.55 32  ?  ?
Wood Metal Dry and clean 0.2 - 0.6  ? 0.2 - 0.54 11.3 - 31  ?  ?
Wood Metal Wet 0.2  ? 0.2 11.3
Wood Wood Dry and clean 0.25 - 0.5  ? 0.24 - 0.46 14 - 26  ?  ?
Wood Wood Wet 0.2  ? 0.2 11  ?  ?
Mild steel Mild steel Dry and clean 0.74 0.57 0.64 37 0.52 30
Hard steel Hard steel Dry and clean 0.78 0.42 0.66 38 0.40 23

For more, see The Engineer's Handbook and Engineering Toolbox.


External links

Instructional video links