Sound frequency

The shape of waves is rolling peaks and valleys. If the wave moves faster, the peaks and valleys form closer together. If it moves slower, the waves spread out.

• The speed of a sound wave - how fast the waves move from peak to trough - is called frequency, but we also know it as pitch. We measure sound frequency in hertz (Hz), which is the cycles per second.
• Understanding frequencies is useful. For example, you can tune an instrument - middle C on the piano is tuned to the frequency of 261.63 Hz.