How does a longitudinal wave differ from transverse and torsional waves?

Question

Also, since sound waves are the most common longitudinal waves, how can I know whether or not it IS a sound wave?

Answer 1

Hello Ashley -

A longitudinal wave is like a compression wave that travels along a Slinky (or similar long, soft spring) when you hold it up by one end and then "bounce" that end down and up again along the axis of the Slinky. The compression wave will travel along the length of the Slinky, and bounce off any obstruction at the end.

A transverse wave is probably best represented by the waves on the surface of the ocean, where the wave form is characterized by peaks and troughs that travel along the medium. Notice that a small object floating on the surface will move up and down as the wave passes, but movement in the direction of the wave propagation will be minimal. A vibrating guitar string is another example of a transverse wave, although the sound it creates forms longitudinal waves in the surrounding air.

A torsional wave is represented by a drive shaft with a wheel mounted to one end. If you twist the shaft back and forth - clockwise and counter-clockwise at the natural frequency, you will set up a torsional wave as the wheel inertia twists the shaft in a torsional resonance.

Sound waves are just pressure waves in the air. As long as they are within the range of human hearing, you can detect them with your ear. Beyond those frequencies, you can still pick them up with a microphone and an amplifier.