Work

Work is a concept relating the amount of energy gained or lost over a time interval. For example, if 5kJ of energy was gained over a time interval of 2 seconds, the work value would be 2.5 kJ/s. This value is represented in watts, in which 1 W = 1J/s, so 2500 W.

Example of work done

Previous picture is a young man climbing stairs. He does this 4 seconds (Hint: it's me!). Minimum energy that he had done can be calculated by potential energy when he reaches the top.

The potential energy is equal to 1455.3 J. Because this energy was exerted over a time interval of 4 seconds, the work value is 363.8 W, or .488 horsepower.

Another example of work done

Picking up a 15 lb (6.81kg) a height of 4 meters in 1 second.

PE/t = 267.0W = .358hp

An example of work not being done analogous to the second example would be holding the object still at 4 meters over a time interval. Over that time interval, no energy is neither gained nor lost. Therefore, no work is done.