Power is the ability to do useful work. Car engines and other motors like garage door openers are often rated by their number of horsepower. Watts, as in a 60 watt lightbulb, is another measure of power. In the case of a car engine, the useful work is the rotational motion that turns the wheels. For a lightbulb, the useful work is the amount of light that it provides.

There are two components of power, force and speed. In the rotational case, this becomes torque and rotational speed. This can be written as power = force x velocity or power = torque x rotational speed. In the metric system, power is measured in units of Watts. A Watt is 1 Newton (force) times 1 meter per second (speed). For rotational power, 1 Watt is 1 Newton-meter (torque) times 1 radian per second (rotational speed). A radian is 180/pi or about 57.296 degrees.

In the English system, power is measured in foot-pounds per second. Many times, we hear the expresssion horsepower. 1 horsepower is 550 foot-pounds per second of power. Motors, like the Lego‘ motor, can only deliver a finite amount of power that cannot change. What does change is the tradeoff between the amount of torque and the amount of speed. For instance, the Lego motor rotates at a very high speed, but does not have much torque. By using gears, you can increase the amount of torque that your robot has, but with a decrease in speed. So, machines can either be strong and slow, or fast and weak. You must decide which is best depending on the type of problem that you are trying to solve.