Friction Stopping Distance Calculator
Find how far and how long an object slides to a stop under kinetic friction from its speed and the friction coefficient.
How it works
a = μ·g · d = v² ÷ (2·μ·g) · t = v ÷ (μ·g)
On a level surface the only force stopping a sliding object is kinetic friction, which produces a deceleration a = μg — independent of mass, since the friction force and the inertia both scale with weight. The stopping distance grows with the square of speed, so doubling your speed quadruples the distance needed to stop; that is why highway braking distances are so much longer than city ones.
Worked example
A car sliding at 20 m/s on dry asphalt (μ = 0.7, g = 9.81 m/s²) decelerates at 0.7 × 9.81 = 6.867 m/s². Stopping distance = 20² / (2 × 6.867) = 400 / 13.734 ≈ 29.1 m, taking 20/6.867 ≈ 2.9 s to stop.
Sources: Friction — Wikipedia
Frequently asked questions
Does a heavier object stop in a shorter distance?
No. Mass cancels out: both the friction force and the momentum scale with mass, so the deceleration μg — and therefore the stopping distance — is the same for a light car and a heavy truck on the same surface.
Why does doubling speed more than double the distance?
Stopping distance depends on speed squared (d = v²/2μg). Twice the speed carries four times the kinetic energy, so it takes four times the distance to dissipate through friction.
Does this include reaction time?
No — this is the pure sliding (braking) distance once friction acts. Total stopping distance for a driver would add the reaction distance travelled before the brakes engage.
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This calculator is for educational purposes. Double-check important results before acting on them.