# Acoustics

Sound is defined as the propagation of a mechanical compression front or longitudinal wave, propagating three-dimensionally through space and only in material media such as air or water.

For this propagation to occur, compressions and rarefactions must occur in medium propagation. These waves propagate longitudinally.

As it passes, the sound wave does not drag air particles, for example, it only causes them to vibrate around their equilibrium position.

As sound waves must be periodic, the propagation velocity ratio is valid: Normal human hearing can pick up sound wave frequencies ranging from approximately 20Hz to 20000Hz. These are called infrared waves, waves that have a frequency below 20Hz, and ultrasound ones that have a frequency above 20000Hz.

So that: The speed of sound in water is approximately 1450m / s and in air at 20 ° C is 343m / s.

The propagation of sound in gaseous media strongly depends on the gas temperature, it is even possible to demonstrate experimentally that the velocity of sound in gases is given by: Where:

k = constant depending on the nature of the gas;

T = absolute gas temperature (in kelvin).

As an example we can take the velocity of sound propagation in air at a temperature of 15 ° (288K), which has a value of 340m / s.

Example:

Knowing that at 15 ° C the sound propagates at 340m / s, what will be its propagation speed at 100 ° C?

Remembering that:

15 ° = 288K

100 ° = 373K 