Imagine using a flick of your wrist to create a traveling transverse square wave in a string vs. in a long metal dowel. It's actually not so hard to create a s

Imagine using a flick of your wrist to create a traveling transverse square wave in a string vs. in a long metal dowel. It's actually not so hard to create a smooth sinusoidal wave in a metal dowel. (It will be long wavelength, but it will be easily visible if you put your eye near one end and look down it.) But it would be impossible for you to make a square wave.