# Power

How fast energy is transferred, P = work / time. The unit is the watt, one joule per second.

Physics (university) · Part 03: Work, energy and momentum · Card 6 of 9 · Last updated 2026-10-19

## Analogy

Two people climb the same stairs. The faster climber has more power.

## Example

**Lifting load**

W = 60 x 9.8 x 3 = 1764 J
P = 1764 / 5
P = 353 W

## In practice

Lifting a 60 kg load 3 m in 5 s takes about 350 W.

## Practice

### Flashcards

- **What is one watt?** One joule of energy transferred each second.

## Questions people ask

### How many joules does a 100 W bulb use in an hour?

Energy is the total amount transferred, in joules. Power is how fast it is transferred, in watts. A 100 W bulb uses 100 J every second. Run it for an hour and it uses 360,000 J. Power says the rate, energy says the total.

### How do I convert watts to horsepower?

One mechanical horsepower is about 746 watts. To convert, divide the watts by 746. A 100 kW engine produces about 134 horsepower. Physics courses use watts, but car adverts still use horsepower, so the conversion sometimes appears in exam problems and in car brochures too.

## Related concepts

- [Work](https://studyvisually.com/learn/science/physics-university/physics-university-part-3/physics-university-part-3-concept-1)
- [Kinetic energy](https://studyvisually.com/learn/science/physics-university/physics-university-part-3/physics-university-part-3-concept-2)
- [Work-energy theorem](https://studyvisually.com/learn/science/physics-university/physics-university-part-3/physics-university-part-3-concept-3)
- [Gravitational potential energy](https://studyvisually.com/learn/science/physics-university/physics-university-part-3/physics-university-part-3-concept-4)

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