By Zencalcy Editorial TeamLast reviewed About us
Friction always opposes sliding, so it does negative work on a moving object: it removes mechanical energy and turns it into heat and sound. On a level surface the friction force is μmg; on a slope only the normal component, mg cos θ, matters.
Energy dissipated by sliding friction over a distance.
W_f = μ m g cos θ · d
W_f is the (negative) work done by friction, μ the kinetic friction coefficient, m the mass, g standard gravity, θ the slope angle and d the distance slid. On level ground cos θ = 1.
| Symbol | Meaning |
|---|---|
| W_f | Work done against friction (energy dissipated), in joules. |
| μ | Coefficient of kinetic friction, dimensionless. |
| m | Mass, in kilograms. |
| d | Sliding distance, in metres. |
| θ | Angle of the surface above the horizontal. |
On a level floor the friction force is 0.3 × 10 × 9.80665 = 29.42 N, so 5 m of sliding dissipates 147.1 J — enough to raise the block's temperature slightly.
Continue with the Efficiency Calculator, Elastic Potential Energy Calculator, or the Kinetic Energy Calculator — or browse more work, energy and power tools and all physics calculators.
The friction force points opposite the displacement, so the angle between them is 180° and cos θ = −1. The magnitude is the energy removed from the object's motion.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Content updated: September 2026