The frequency of a wave or vibration is the number of times the wave or vibration passes by completely per second. The frequency is measured in Hertz (Hz). This is a unit equal to one cycle per second.
The formula to determine the frequency is
f = 1 / T
where 'f' is the frequency and 'T' is the period of the wave or vibration. The period is the time it takes for one complete cycle.
Imagine you have a swing. As the swing goes back and forth, it does this in a certain amount of time. We call this time the period. If, for example, it takes 2 seconds for the swing to go from one extreme to the other and back again, then the period is 2 seconds.
To calculate the frequency, we divide 1 by the period. So in our example, we would divide 1 by 2 to get a frequency of 0.5 Hz. This means that the swing completes a full cycle half a time per second.