# Wave Momentum

1. Sep 17, 2007

### Maxwell's Demon

Apparently what I thought I understood about waves is wrong: there seems to be a net momentum transfer with mechanical waves, as well as photons (it seems they're perfectly analogous). I hope some of the experts on the board can help to clarify this issue; perhaps it’s less surprising to others here than it is to me.

I recently found this discussion on the topic of wave momentum started by Carl Mungan, Associate Professor at the US Naval Academy: http://www.usna.edu/Users/physics/mungan/Scholarship/WaveMomentum.html There’s a list of references at the bottom of the page, and this reference was cited in Dr. Mungan’s last post as his key reference: Reuben Benumof, "Simple harmonic motion in harmonic waves," AJP 48, 387-392 (May 1980)

If this is true, then everything else I’ve read online about wave momentum, and all the applets I’ve seen, are wrong (or at least confined to one special case scenario). And following the discussion in that link, it appears that most physics professors also incorrectly believe that mechanical waves transfer zero net momentum.

This question has gotten me thinking that maybe we can interpret any wave in the manner QM describes photons, as both a wave and a particle.

Help?

2. Sep 17, 2007

### genneth

Indeed any wave can be quantised -- leading to a particle of that particular wave. In condensed matter physics this is often done, leading to phonons, plasmons, etc.

3. Sep 18, 2007

### Maxwell's Demon

Thanks genneth. It gives one a whole new perspective to look at macroscopic phenomena like waves on water as ‘wavicles.’ Weird.

I’m having some trouble finding the method for determining the net momentum of a sound wave – all the papers in Munga’s thread cost $19/ea for us untermenchen. I'd like to see what it would take to build a self-lifting ultrasonic acoustic levitation device (driven by an external power source). Here's a video of acoustic levitation, which I think is pretty cool stuff: http://video.google.com/videosearch?q=acoustic+levitation&hl=en Anyone got those equations handy? I’d be much obliged (well at least$19 worth ;)

Last edited: Sep 18, 2007