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What is sound?

String players in an orchestraSound is made when something vibrates (shakes). The molecules in the air (or a liquid or solid) are rapidly pushed together and pulled apart. Musical instruments make pleasing sounds. Noise is an unpleasant mix of many sounds.



The many sources of sound on a busy street


Birdsong, a high-pitched sound

Pitch

Slow vibrations make low sounds. Fast vibrations make high sounds. The low-ness or high-ness of a sound is called its pitch. An example of a low-pitched sound is the rumble of a jet engine or the beat of a pop song. Birdsong is an example of a high-pitched sound. 

Sound travels more slowly through air than through water, and more slowly through water than through steel. Sound travels more than 10 times faster through steel than through the air.

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