Power
How fast energy is transferred, P = work / time. The unit is the watt, one joule per second.
Last updated
Analogy
Two people climb the same stairs. The faster climber has more power.
Example
W = 60 x 9.8 x 3 = 1764 JP = 1764 / 5P = 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.