What is noise?

Noise is a complex sound produced by various vibrations, that are often absorbed and are not harmonic.

Sound is an auditory sensation (involving physiological and psychological phenomena) generated by a sound wave (physical phenomenon).

Sound waves

In air, sound propagates as a variation of pressure created by a sound source. Sound is an acoustic wave, where only the compression moves and not the air molecules.

When circles (ripples) are observed in water, the waves move but the water remains in the same place. It only moves vertically and does not follow the waves. A cap placed on water remains in the same position without moving; it merely oscillates up and down. It's the same thing in the case of sound; only the compression moves and not the air molecules.

Speed of sound and calculation of distance

Sound waves travel at about 344 meters/second (in air at 20° C).

How to calculate the distance of a storm?

  • The speed of light is 300,000,000 m/s and can be considered as almost instantaneous.
  • Count the number of seconds between lightning and the rumble of thunder.
  • Divide this by 3 to obtain the number of kilometers that separate us from the storm.

Light takes about 1.3 seconds to reach the moon (384,000 km), while sound will require 310 hours to travel the same path. This example is just to give an idea of the difference between the speed of sound and the speed of light. As we shall see, in space, sound does not travel (vacuum).