BDeTar@AOL.COM wrote: > > List, > > If you think about string vibration, it's easy to see that the string > vibrates up and down. It also vibrates side to side AND back and forth. > It's this back and forth vibration that is the longitudinal wave. To > demonstrate this, try clamping a long (4-6 foot or so) metal bar to a table. > Place a marble at one end of the rod, making sure it is touching the end of > the rod. Next tap the other end of the rod with a small mallet. Watch as > the marble is propelled away from the end of the rod. You have just > witnessed a LONGITUDINAL WAVE in action! > > Here's a quick way to test a bass note to discern whether that high "squeal" > or harmonic is coming from a longitudinal wave or a hard spot in the hammer. > Drop the pitch about 1/2 or 1 whole step. Because the AMPLITUDE (volume) of > the longitudinal wave is a product of tension, it will disappear when the > tension of that string is reduced. In fact, as you drop the tension of the > string, you can listen for when the longitudinal wave disappears! If, > however, when you drop the tension that high harmonic is still present, your > culprit is typically a hard spot very near the crown of the hammer. > > Hope this answers your question! > > As a PS, if anyone is interested, I believe I still have the formula for > predicting the frequency of a longitudinal wave. It's a nice formula, but > frankly, I think a formula to predict the AMPLITUDE of the wave is of more > value. > > Ain't information wunnerfull?! > > Brian De Tar, RPT > Portland, OR > BDeTar@aol.com > NO OBSTACLES... ONLY OPPORTUNITIES! Oh, so there is real longitudinal motion in a string? I'd be interested at which frequencies this takes place! Jos.
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