A sound wave is called a longitudinal wave because compressions and rarefactions in the air produce it. The air particles vibrate parallel to the direction of propagation.
The vibration of the medium that travels along or parallels the direction of the wave is called a longitudinal wave. Sound waves can only travel in space if enough particles are around to transmit the energy in the wave from the source to the listener.
- The frequency of a sound wave is what your ear understands as pitch.
- A higher frequency sound has a higher pitch, and a lower frequency sound has a lower pitch.
- The human ear can detect a wide range of frequencies. Frequencies from 20 to 20000 Hz are audible to the human ear.
- Any sound with a frequency below 20 Hz is known as infrasound, and any sound with a frequency above 20000Hz is known as an ultrasound.