Sunday, May 25, 2008

Sound waves

4 comments:

jb said...

Ahh, modal resonance of plates. How I don't miss some things from my college studies...

shannon said...

whoa- someone please explain!

ScrewGoogle said...

As I recall, this is just a function of the frequencies at which a structure will resonate. The classic engineering example is the Tacoma Narrows Bridge. The sand settles at the zero-crossing points of the waves (imagine a sine wave crossing the x axis) and as frequency increases, these points become more frequent. How they arrange themselves is specific to the plate.

I'd need to do some fact checking to be sure, but that's how I remember it. Jello is the structural engineer... so he could correct me.

jb said...

You're absolutely correct in your explanation. I could pull out a textbook or two and give the mathematics of each mode, but I don't want to.

Only bit to add is that the messy time between perfect resonance is due to multiple vibration waves occuring, i.e. no constantly zero crossover point. Waves of one frequency added to waves of another frequency (and etc) scatters the sand.