Re: Does sound also have momentum?

Very good question, Darius. Sound is the propagation of acoustic energy 
through a medium such as air or water. Although the energy propagates as 
waves, like light or other electromagnetic energy, acoustic energy is 
mechanical energy. Unlike light, where the waves can also be 
interpreted as particles, sound waves propagate through the oscillation of 
particles in a medium. The individual particles of air or water don't 
actually move very far, they just oscillate in place carrying the sound 
wave further to the next particles ahead. This is why sound doesn't 
propagate in a vaccuum but light does; sound requires a medium of particles 
to propagate the acoustic energy while light sort of propagates itself.

Although the individual particles propagating the sound wave have mass and 
momentum while they're in motion, the wave itself has no momentum. So sound 
waves don't have a dual nature.

However, you can transfer energy with sound--and do work--because the 
individual particles have energy and momentum as they oscillate. Air 
molecules inside your ear set into motion by the energy of an acoustic wave 
hit your eardrum and transfer their momentum to it which cause it to 
vibrate, which lets you hear the sound. Acoustic energy has even been used 
to levitate small objects against gravity--but you need a very loud sound 
to do that. You can find out more about this by searching the web for 
"acoustic levitation".

Hope that answers your question. Please email me if you have any further 
questions.

Best,
  Adams Douglas
  Senior Developer
  Dicon, Inc.