Friction

• Friction always opposes motion or the applied force (called a non-conservative force)

• Force due to the rubbing of two surfaces against each other

• Typically…..

• 0< μ < 1

• 0 would be “frictionless” and μ=1 is really “sticky”

5.29 micrometer (μm) = 1/500 inch

A magnified view of a frictionless coating

The road from static to kinetic friction

Friction (types)

• Kinetic Friction: this is moving friction

• Static friction: this is non-moving friction

• Static friction > sliding friction

Both friction types are defined by the coefficient of friction, μ (either kinetic, μk or static, μs)

Fiction Equations

k k N

s s N

f F

f F