8.2 - Period
Period: The amount of time it takes for an
object to return to the same position.
The concept of period is useful in analyzing motion that repeats itself. We use the
example of the toy train shown in Concept 1 to illustrate a period. The train moves
around a circular track at a constant rate, which is to say in uniform circular motion. It
returns to the same position on the track after equal intervals of time. The period
measures how long it takes the train to complete one revolution. In this example, it
takes the train six seconds to make a complete lap around the track.
When an object like a train moves in uniform circular motion, that motion is often
described in terms of the period. Many other types of motion can be discussed using
the notion of a period, as well. For example, the Earth follows an elliptical path as it
moves around the Sun, and its period is called a year. A metronome is designed to
have a constant period that provides musicians with a source of rhythm.
The equation on the right enables you to calculate the period of an object moving in
uniform circular motion. The period is the circumference of the circle, 2 ʌr, divided by
the object’s speed. To put it more simply, it is distance divided by speed.
Period
Time to complete one revolution