Vibrations in the air

Principle
The cork particles have been set in motion by the vibration of the tuning fork. Since the tuning fork has no direct contact with the cork flour, the movement must have been passed on via the air lying between them. By the movement of the cork flour one has thus made the vibrations of the air visible. This is how the perception of sounds and noises can be explained: The movement of a body causes a vibration of the air, which continues to the ear, where it is registered by the sensory cells.