Two motors can lift the same crate to the same shelf, transferring the same energy, yet one finishes in a second and the other takes a minute. The difference is power: not how much energy is moved, but how quickly it is moved.
Power is the rate of doing work, or the rate of transferring energy: P = W ÷ t = ΔE ÷ t. It is measured in watts (W), where one watt is one joule per second.
Power is the work done, or energy transferred, per unit time.
One watt is one joule per second.
Set the energy to transfer and the time taken, then run it. The power readout shows how the same energy delivered in less time means a higher power.
Four quick checks on the definition, equation and unit of power. Each correct answer earns XP and lights this skill on your star map.
Power is defined as the...
Power is calculated using the equation...
Power is measured in...
One watt is equal to...
The defining equation and its rearrangement for energy:
A pump does 24000 J of work in 40 s. Find its power output.
Power is not the same as energy. Energy, in joules, is the amount transferred; power, in watts, is how quickly it is transferred. Two machines can transfer exactly the same energy while having very different powers, simply because one takes longer than the other. Always divide the energy by the time.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
A motor transfers 600 J of energy in 30 s. Its power is...
A 1500 W heater runs for 60 s. The energy it transfers is...
Two cranes lift identical loads to the same height. Crane A takes 10 s, crane B takes 20 s. Compared with crane B, crane A...
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