Sound bends around obstacles because pressure changes cannot end abruptly at shadow boundaries

Evidence

Diffraction occurs because the variations in air pressure, due to the com­ pressions and rarefactions in the sound wave, cannot go abruptly to zero after passing the edge of an object. This is because there is interaction between the adjacent molecules that are propagating the wave. In order to allow the compressions and rarefactions to die out gracefully in the bound­ ary between the wave and the shadow, there must be a region in which part of the propagating wave changes direction, and it is this bent part of the wave that forms the diffracted component. — David Howard, Jamie Angus, coustics and Psychoacoustics, 417

Categorization

• DEFINE: Explains the physical mechanism underlying diffraction of sound waves.