How often it shakes

Pluck a rubber band: pull it and let go. Stretch it tighter and pluck again. The note goes higher.

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.

Try the lab to finish this lesson.