Anacoustic zone
Encyclopedia
The anacoustic zone is the region of the atmosphere of Earth above about 160 kilometres (99.4 mi) where there are still enough gas molecules to produce substantial drag
, but they aren't close enough to transmit sound
because the probability of molecular collisions is so low.
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
, but they aren't close enough to transmit sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
because the probability of molecular collisions is so low.