Power
Rate of doing work.
Formula
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Example
Doing 600 J of work in 3 s delivers P = 600/3 = 200 W.
How it works
Power tells you how quickly work is being done. If the same amount of work is completed in less time, the power is larger, because the energy transfer happens faster. Since work is measured in joules and time in seconds, power is measured in watts, where 1 W = 1 J/s.
When to use it
Use this formula when you know the amount of work done and how long it took, such as lifting objects, moving against friction, or comparing the output of machines and engines. It is also useful anytime you want to measure the rate of energy transfer.
Worked example, step by step
A machine does 900 J of work in 15 s. P = W / t P = 900 / 15 P = 60 W So, the power output of the machine is 60 watts.
Common mistakes to avoid
- Using the formula with time in minutes instead of converting to seconds first
- Confusing power with total work or energy
- Reversing the formula and calculating W / P instead of W / t
Did You Know?
One horsepower was defined by James Watt from how much a real horse could lift in a minute.
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