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Friction Calculator

Calculate friction force and coefficient

Force Calculator (F = ma)

kg
m/s²

Friction is the force resisting relative motion between surfaces. Static friction prevents motion from starting; kinetic friction acts during motion. Friction force = coefficient of friction (μ) × normal force (N). Higher μ means more friction.

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Tip: On an incline, an object starts sliding when tan(θ) > μₛ. For μₛ = 0.5, sliding begins at θ = arctan(0.5) ≈ 26.6°. This is called the angle of repose — used in soil engineering.

  1. 1F_friction = μ × N (normal force)
  2. 2Static friction (max): μₛ × N (before motion starts)
  3. 3Kinetic friction: μₖ × N (during sliding, usually μₖ < μₛ)
  4. 4Normal force = weight × cos(θ) on an incline at angle θ
10 kg box, μ = 0.4, flat surface=F_friction = 0.4 × 98.1N = 39.2 NNormal force = mg = 10 × 9.81
SurfacesStatic μₛKinetic μₖ
Rubber on concrete (dry)0.6–0.80.5–0.7
Rubber on wet concrete0.4–0.60.3–0.5
Steel on steel0.6–0.80.5–0.6
Wood on wood0.25–0.50.2–0.4
Ice on ice0.03–0.10.01–0.03
Teflon on Teflon0.040.04

Fun Fact

Car braking uses friction between brake pads and rotors. ABS (Anti-lock Braking System) rapidly alternates between static and kinetic friction — static friction is higher, so ABS keeps you at the max braking force without wheel lockup.

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