Do you want to hear the most annoying sound in the world? What about watching the most annoying sound in the world levitate objects? Acoustic levitation takes intense sounds and reflects them back on themselves, producing what's known as a standing wave—a sound wave that seems to kind of vibrate in place, rather than traveling the way a normal wave does.
Ordinary standing waves can be relatively powerful. For example, a standing wave in an air duct can cause dust to collect in a pattern corresponding to the wave's nodes. A standing wave reverberating through a room can cause objects in its path to vibrate. Low-frequency standing waves can also cause people to feel nervous or disoriented — in some cases, researchers find them in buildings people report to be haunted.
The kind of high-decibel standing waves used in acoustic levitation can actually create pockets of air pressure strong enough that objects inside them can resist the pull of gravity. This particular acoustic levitator was designed by physicist David Deak in 1987, to help NASA mimic the low-gravity environment of the space shuttle, on Earth.
How Stuff Works: How Acoustic Levitation Works
Thumbnail image courtesy Flickr user trialsanderrors via CC
