The boom of thunder sounds very different from the squeal of a car braking. The difference is basically in the frequency of the waves that produce the sound. If the waves follow each other in quick succession, they produce a high frequency, high-pitched sound. If they follow only slowly, the sound is low frequency or low-pitched. Overtones Most sounds contain a mixture of different frequencies - a basic or fundamental pitch and a range of overtones.
Overtones help make sounds recognizable.
A flute, for instance, has quite a pure sound with most overtones in harmony with the fundamental. A violin has a brighter sound with harsh overtones. Speed of sound Sound travels at different speeds in different substances, and travels faster in warm air than cold air. In pure water, it reaches 1500m per second, and in solid steel it travels at 6000m per second. Sound waves ripple out in all directions from the sound source, gradually losing energy.