How often it shakes
Pluck a rubber band: pull it and let go. Stretch it tighter and pluck again. The note goes higher.
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Rule
Frequency is the number of complete shakes in one second. Its unit is the hertz. A higher frequency is heard as a higher pitch. Frequency × time period = 1.
- Frequency — complete shakes in one second. One shake a second is 1 hertz (Hz).
- Time period — the time for one complete shake.
- Pitch — how high or low a sound seems.
Time period is written T. Frequency is written f or ν (nu). A tighter band shakes more often. So its pitch is higher.
A string shakes 6 times in 3 s. Frequency = 6 shakes ÷ 3 s = 2 Hz. Time period = 3 s ÷ 6 shakes = 0.5 s. Check: 2 × 0.5 = 1.
Watch out!
Pitch is not loudness. A high note can be soft. Frequency sets pitch. Amplitude sets loudness.