In physics, work has a precise meaning: a force doing work only when it moves something, with W = F·d measuring the energy transferred. Power then measures how fast that energy is delivered — the work divided by the time, in watts. The same job (lifting a load, pushing a crate) always takes the same work, but doing it quickly demands more power. That single distinction — total energy versus rate of energy — separates a strong machine from a fast one, and underlies every motor and engine rating.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the definitions of mechanical work and power.
The work & power equations
With force in newtons and distance in metres, work comes out in joules; divide by seconds for power in watts. The cosine term handles a force applied at an angle — only the component along the direction of motion does work, so a force perpendicular to the path (like the tension in a string whirling a ball) does none. The P = F·v form is the handy one for steady motion, linking a pushing force directly to the power at a given speed.
Worked example — pushing a crate
Scenario: Pushing a crate with 200 N over 15 m, taking 10 seconds, force aligned with the motion.
The push transfers 3,000 joules of energy over the 15 m, and at a steady pace over 10 seconds that is 300 watts of power. Do the same job in 5 seconds and the work is unchanged at 3,000 J, but the power doubles to 600 W — you are working twice as fast. If the force were applied at 60° to the motion instead, only cos 60° = half of it would count, halving the work to 1,500 J.
Frequently Asked Questions
W = F × d (× cos θ if angled). 200 N over 15 m = 3000 J. No movement = no work.
P = W/t (watts), or P = F·v. 3000 J in 10 s = 300 W.
Work = energy transferred (J); power = how fast (W). Running upstairs = same work, more power than walking.
hp = W ÷ 745.7. 300 W ≈ 0.40 hp; 1 kW ≈ 1.34 hp. Metric PS uses 735.5 W.
No — no displacement, no work. W = F×d = 0 when d = 0, even though your muscles tire.