What is this a demonstration of?

Question

http://video.stumbleupon.com/#p=67kfd7upiw

Answer 1

Thanks, that was interesting.  It demonstrated resonance.  The surface of a liquid (or membrane) was organized into standing (motionless) waves depending upon the sound frequency.  Sprinkled particles permit the crests and troughs to be visialized.  As the frequency of the sound is increased, the waves become smaller and smaller and their patterns more and more complex.  When you pluck a guitar string it vibrates in a complex manner dividing the string into halves, thirds and fourths, etc. to produce harmonics.  The demonstration is more like the way a drumhead responds depending upon where it is struck with a drumstick.  If you push someone on a swing you can increase (or maintain) their kinetic energy with pushes in step with their swing (which is similar to resonance).

Answer 2

I agree with the first answer and would like to also include that this demonstrates how various sound frquencies are used in medical scanning such as CTs. The sound waves basically bounce off of the internal organs and form a picture for the technician.