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When work is done on an object, energy is transferred. The rate at which this energy is transferred is called power. So the more powerful a device is, the more energy it will transfer each second.

Calculating power

The equation used to calculate power is:

This is when:

• power (P) is measured in watts (W)
• work done (W) is measured in joules (J)
• time (t) is measured in seconds (s)

One watt is equal to one joule per second (J/s). This means that for every extra joule that is transferred per second, the power increases by one watt.

Example

Two electric motors are used to lift a 2 N weight through a vertical height of 10 m.

Motor one does this in 5 seconds.

Motor two does this in 10 seconds.

For both motors:

For motor one:

For motor two:

Since twice as much energy is transferred by motor one each second, it is possible to say that motor one is twice as powerful as motor two.

Learn more on power in this podcast

Listen to the full series on ����ý Sounds.