The friction calculator computes static and kinetic friction forces using F = μN, with a built-in database of 13 common surface material pairs. Supports inclined surfaces and both metric and imperial units.
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How to Use the Friction Calculator
Friction is the force that resists relative motion between surfaces in contact. This calculator computes both static friction (preventing motion) and kinetic friction (opposing ongoing motion) using F = μN, where μ is the coefficient of friction and N is the normal force.
Example: Car Braking Distance
A 1500 kg car brakes on dry concrete (μk = 0.8). Normal force N = 1500 × 9.81 = 14,715 N. Kinetic friction force = 0.8 × 14,715 = 11,772 N. Using Newton's second law (F = ma): deceleration a = 11,772 / 1500 = 7.85 m/s². From 60 km/h (16.67 m/s) to stop: d = v²/(2a) = 277.9/15.7 ≈ 17.7 m.
Using the Material Database
Select a surface pair from the dropdown to auto-fill static and kinetic coefficients. These are typical published values — actual coefficients vary with surface condition, temperature, and lubrication. Use "Custom" to enter your own values.
Inclined Surfaces
Enter an incline angle to account for slope effects. On an incline at angle θ, normal force = mg × cos θ, and the gravitational component along the slope is mg × sin θ. The calculator checks whether the object would slide (if gravity component exceeds maximum static friction) and shows the acceleration down the slope if it does.
Applied Force and Acceleration
Enter an optional applied force (parallel to the surface) to find the net force and resulting acceleration. If the applied force exceeds maximum static friction, the object slides and kinetic friction applies. Net force = Applied force − Kinetic friction force.
FAQ
What is the friction force formula?
Friction force is calculated using F = μN, where μ (mu) is the coefficient of friction and N is the normal force. On a flat surface, N = mg (mass × gravity). On an incline at angle θ, N = mg × cos θ. Static friction (μs) is typically higher than kinetic friction (μk).
What is the difference between static and kinetic friction?
Static friction acts on objects at rest — it opposes the tendency to slide and can vary from zero up to a maximum of μs × N. Kinetic (sliding) friction acts when objects are already moving — it equals μk × N. Since μs > μk for most surfaces, it takes more force to start sliding than to maintain it.
What is a typical coefficient of friction for tires on road?
Rubber on dry concrete has μs ≈ 1.0 and μk ≈ 0.8. Rubber on wet concrete drops to μs ≈ 0.7 and μk ≈ 0.5. This is why stopping distances increase significantly in wet conditions — braking force is reduced by about 40%.
How does an incline affect friction?
On an incline at angle θ, the normal force is N = mg × cos θ instead of mg, which reduces friction. However, the component of gravity along the slope is mg × sin θ, which tends to slide the object. The object stays put if μs × cos θ ≥ sin θ, i.e., if the incline angle θ ≤ arctan(μs).
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally in your browser. Nothing is transmitted to any server.
What surface has the lowest coefficient of friction?
Teflon on Teflon has one of the lowest friction coefficients — μs ≈ 0.04. Steel on ice (skate blade) is also very low at μk ≈ 0.01. Ice on ice has μk ≈ 0.03. In contrast, rubber on dry concrete (μs ≈ 1.0) is among the highest for common surfaces.