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Physics -- Units and Concepts: Energy |
Work is done when a force travels some distance. The weight driving a grandfather clock overcomes the friction of the clockwork and during its work the weight goes down a certain distance, say 1m, before you have to lift it up again. If the weight has a mass of 1020 g (slightly more than a kg) it will pull on the chain with a force of 10 N. This force has travelled in its own direction by 1m. The amount of work done is 10 Nm, 10 Newton-metre.
The unit of work is 1 Nm, which is named a Joule or J in honour of James Joule who demonstrated the equivalence of mechanical work and heat in 1845.
Work or energy can be stored e.g. as chemical energy, for later use. Originally there was a measure of heat, separate from that of work: the calorie, a bad unit. Electrical energy is often measured in kWh, another bad unit.