Coefficient of Friction: Steel on Steel (Dry)

Friction Data: Steel on Steel

Hard steel on hard steel. Most common engineering friction pair.

Type	Coefficient (μ)	Description
Static (μs)	0.5-0.8	Force to start motion
Kinetic (μk)	0.42	Force during sliding

How to Use This Value

The coefficient of friction is used in the fundamental friction equation:

F_friction = μ × N

Where F is the friction force, μ is the coefficient of friction, and N is the normal force (perpendicular to the surface).

Example Calculation

A 100 kg block of steel rests on a steel surface (dry). How much force is needed to keep it sliding?

F = μ × m × g = 0.42 × 100 kg × 9.81 m/s² = 412.0 N (42.0 lbf)

Static vs. Kinetic Friction

Two types of friction coefficients exist for every material pair:

• Static friction (μ_s) — the force needed to start an object moving. Almost always higher than kinetic friction.
• Kinetic friction (μ_k) — the force needed to keep an object sliding. Lower because contact asperities are continuously breaking and reforming.

This is why objects “jerk” when they first start moving — the force drops suddenly as you transition from static to kinetic friction.

Practical Tips

• Surface finish: These values assume typical machined or ground surfaces. Polished or rough surfaces will differ.

Related Material Pairs

• Steel on Steel (lubricated) — μ = 0.16
• Aluminum on Steel (dry) — μ = 0.61
• Brass on Steel (dry) — μ = 0.51
• Brass on Steel (lubricated) — μ = 0.19
• Bronze on Steel (lubricated) — μ = 0.16
• Copper on Steel (dry) — μ = 0.53