Don't talk behind my back-but why not?

In grade school we all learn that when you have a secret, you whisper it behind someone's back.

Why? Isn't whispering alone sufficient, even in front of someone?

Believe it or not, whispering actually works better behind someone's back than in front of them, and not just because they can't see you.

The trick to whispering has to do with the nature of sound. Sound proceeds outward from its source in waves. When these waves reach someone's ear, they are translated in the brain into a perception of sound.

However, not all waves travel around things equally well. A long wave has an easy time going around a corner, for example, because longer waves can bend to get around things. Short waves, on the other hand, can't bend as much. When they hit an object they bounce back or become scattered.

Your head is such an object. Because they bend, longer sound waves can get around your head easily and be heard even when coming at you from behind. Not so short waves.

Now, long waves are what we perceive to be low-pitched sounds. Short ones we perceive as high pitches. The higher the pitch, the shorter the wave. That's the secret to whispering; you not only make your words faint, you give them a higher pitch. Try it and you'll see, whispering naturally ups the pitch of your words.

A high-pitched whisper, with its shorter, non-bending sound waves, will be much harder to hear from behind, unless your ear is very close to its source. If that's the case, you're already in on the secret.