


Power
Power is an important physical quantity that
frequently, though not always, appears on SAT II Physics. Mechanical
systems, such as engines, are not limited by the amount of work
they can do, but rather by the rate at which they can perform the
work. Power, P, is defined as the
rate at which work is done, or the rate at which energy is transformed.
The formula for average power is:
Power is measured in units of watts (W), where 1 W
= 1 J/s.
Example

Power is a measure of the amount of work done in a given
time period. First we need to calculate how much work the piano
mover does, and then we divide that quantity by the amount of time
the work takes.
Be careful not to confuse the symbol for watts, W,
with the symbol for work, W.
Instantaneous Power
Sometimes we may want to know the instantaneous power
of an engine or person, the amount of power output by that person
at any given instant. In such cases, there is no value for to draw upon. However, when a steady force
is applied to an object, the change in the amount of work done on
the object is the product of the force and the change in that object’s
displacement. Bearing this in mind, we can express power in terms
of force and velocity:
