Power is a measure of the amount of work that is being done at a given point in time. If a bulldozer is pushing a pile of soil (or any other device doing work) at a given rate of speed, it is doing a certain amount of work. The actual amount of work being done is determined by the load presented by the soil (the amount of soil being moved) and the rate that the dozer is pushing it. To push the pile faster, the engine would have to produce more power. To push more soil at the original speed, the engine would have to produce more power. Think of pushing more soil as adding more speakers to an amp (wired in parallel - to be covered later). Think of pushing the original amount of soil at a faster rate as driving the speakers harder.
Power to a Speaker:
The power that an amplifier can produce is determined by the load presented by the speaker's voice coil and the amount of electrical force that the amp can apply to the woofer's voice coil. I'll go into more detail on these topics (amplifiers, electrical power, speakers, speaker loads...) later in this tutorial. In the following demo, you can see that the cone only moves a little at low power but more at high power. Click the buttons to switch between no power, low power and high power.
It seems that most everyone wants to get the most power from their car audio amplifiers. Later chapters will cover just how to maximize the output from your amplifier.