MadSci Network: Physics |
Hi Robin,
To understand how sound waves might be able to levitate objects or knock
people over, we first need to understand what they really are. There's a
nice description on the Wikipedia site. I'll
summarize here. Sound waves are waves of compression. A passing wave crest
is manifested by a change in local air or water pressure. When you listen
to your stereo these pressure changes are so small that they're
imperceptible to your sense of touch ; if you hold up your hand, you feel
no force acting on it. Only the very sensitive membranes in our ears pick
up the pressure changes.
If, however, the amplitude of the sound waves is large enough and the
object is small and light enough (for example a tiny droplet of some
substance) it can be held aloft by these pressure changes. If you're
interested in learning more about the physics of levitation, there's a nice
article in
Science .
While some sonic weaponry is real, the sound is generally used to create
discomfort and nausea rather than to knock people over. Weapons that knock
people through the air with sound waves are still firmly in the realm of
science fiction. See this Wikipedia article for more on sonic
weapons.
Cheers,
Tetjana
Try the links in the MadSci Library for more information on Physics.