Sound is caused by the vibration of particles but not all vibrations can be heard as sound. Common ideas about sound come from the limited range of vibrations that human ears can detect.
Part of Combined ScienceWaves
Sound waves are longitudinalcloselongitudinal waveA wave that moves in the same direction as the way in which the particles are moving. waves.
They cause particles to vibrate parallel to the direction of wave travel.
The vibrations can travel through solids, liquids or gases.
When travelling through air, the speed of sound is about 340 m/s.
Sound cannot travel through a vacuumclosevacuumA volume that contains no matter. because there are no particles to carry the vibrations.
The ear is only stimulated by a limited range of frequencies.
This means that humans can only hear certain frequencies.
The range of normal human hearing is 20 Hz to 20,000 Hz, or 20 Hz to 20 kHz.
Any sound above 20,000 Hz is called ultrasound.