Sound waves are longitudinal waves that can travel at different speeds through any medium (solids, liquids, or gases) depending on the properties of the medium. When sound travels through a medium, the medium's particles vibrate in the wave's propagation direction. Individual molecules are displaced longitudinally from their mean positions in this displacement. This causes compressions and rarefactions, which are a series of high and low-pressure areas.
Categories of sound waves based on their frequencies
(a) Audible waves:
These are sound waves with a frequency of \(20\) to \(20,000\) \(hertz\). Vibrating bodies, such as stretched strings, vocal cords and so on, produce these sound waves.
Sound produced by guitar.
(b) Infrasonic waves:
Sound waves with a frequency less than \(20\) \(Hz\) that the human ear cannot detect are known as infrasonic waves.
Seismic waves, ocean waves, whale sounds, and so on.
Sound produced by whales
(c) Ultrasonic waves:
Ultrasonic waves are sound waves with a frequency greater than \(20\) \(kHz\) that are undetectable to the human ear but can be detected by certain animals such as mosquitos, dogs, bats, and dolphins.
Sound produced by bats