Friction Calculator

Friction is the force that resists the sliding of one surface against another, and this calculator works out both its static and kinetic values from the coefficient of friction and the normal force. Static friction is what you must overcome to start an object moving; kinetic friction is what acts once it is already sliding. Both are proportional to the normal force, the force pressing the surfaces together, but they use different coefficients, with static typically being slightly higher. On a flat horizontal surface the normal force equals the object's weight (mass times gravity), so you can enter either the mass in kilograms or type the normal force directly in newtons. The default example uses a static coefficient of 0.5 and a kinetic coefficient of 0.4, each applied to a normal force of 100 N, giving a maximum static friction of 50 N and a kinetic friction of 40 N. This matches the common physics textbook setup where an object at rest on a surface requires more force to start sliding than to keep sliding. The coefficient of friction depends on the pair of surfaces: rubber on dry concrete is around 0.7, steel on steel about 0.2, and ice on ice as low as 0.03. You can also find the normal force from mass alone using g = 9.81 m/s2. Results update as you type. Use this calculator for physics homework, for estimating braking and traction forces, or for understanding why materials with different surface textures behave differently under the same load.

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Friction force = coefficient x normal force. Static friction is the maximum before sliding starts; kinetic applies once sliding. Assumes a flat surface. Rounded for display.