Sound is caused by coliding matter resulting in matter vibrating, creating a sequence of pressure wave that propagates through other matter.

Sound can ony be heard if it is composed of frequencies within the range of one's hearing and of a level sufficiently strong to be heard. For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz)[3], although these limits are not definite. The upper limit generally decreases with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz, but are deaf to anything below 40 Hz.

For an example try hitting a empty glass with a steel spoon. Both glass and spoon will vibrate creating sound, but we can only hear the glass vibrate, because the spoon's vibration is outside our range of hearing.

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