# Period and frequency

Physics Narrative for 11-14

## The relationship between period and frequency

To find the frequency you simply count the number of vibrations each second. An alternative way to do the counting is to find out how long one complete vibration takes and then to calculate how many of these you can get in one second.

The time for one complete vibration is called the period (T) and is measured in seconds.

For example, if the period of a vibration is 0.1 second (one vibration takes 0.1 second), the frequency of the vibration is 10 vibrations per second or 10 hertz.

Notice that:

- If the period is large the frequency is low (relatively few vibrations each second).
- If the period is small the frequency is high (lots of vibrations each second).

More formally, the frequency is inversely proportional to the period. If you double the period, the frequency is halved.

frequency = 1period

You can also write this out in symbols:

*f* = 1*T*