The power delivered to a system is the rate energy is transfered to it. That means it has the dimensions of energy/time. In SI units this is Joules per second. We call that Watts for short. That should be a familiar unit to you, if you and your friends have ever tried to change a light bulb. If you've ever heard a friend bragging about a car, you might be familiar with the unit of horsepower (hp). . So a 25 hp jalopy can keep going a lot of light bulbs!
The average power supplied to say, light bulb, over a
time t is
(1.37) |
(1.38) |
Suppose we have an object and we are pushing it with a force
, what power do we deliver to the object? Well in a time
we do work
. So the power is
(1.39) |