Work is a measure of energy.
If I lift a book of mass **m = 1 kg**
upward a distance of **L = 1 m**
against the force of gravity,
I need to produce

a total of 9.8 Joules of work. Fine.

But it takes the same amount of energy whether I lift the book quickly, in just 1 second, or if I very very sl-o-o-o-o-wly raise the book over 20 seconds. The same number of Joules, yes .... but something is different.

The difference there is in the RATE at which I do work.
We have a name for the rate at which energy is used:
**power**.

Q: What are the units of power?

Let's see how much power a person can produce. We'll run an experiment:

- a volunteer of mass
**m** - will run up a flight or two of stairs, a vertical distance
**H** - over a period of time
**T**

Q: How much work will the volunteer do? Q: How much power will the volunteer produce?

After we've made the measurements and computed the power
of our student volunteer,
we can compare it to the power produced by a
horse.
You may have heard of a "horsepower" -- it is based
on the amount of work that a horse could do over
an entire day.
In metric terms, one horsepower is
about **746 Watts**.

Is our volunteer equal to one horse?

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.