Wednesday, January 24th, 2018

Simple Science: How do we make sound?

Posted on March 02, 2015 in Perspectives
By USM Free Press

Ever wondered what why a door creaks or why you makes sounds when you clap?

What is sound? Well sound is the compression of molecules floating around in the air. These compression move in a pattern forming a wave in three dimensions.

To get a better idea, think of throwing a single rock into the center of the pond. You can see the propagation of a wave in two directions. Now imagine the trough (bottom) of the wave to be where the air molecules are less compressed and the crest (top) to be where the air molecules are most compressed. This is sound.

But a door hinge doesn’t have any space in between its hinges so how does it make sound? This is actually due to friction or the resistance one surface or object encounters when moving over another. When two objects are stationary you get more friction than when one of the objects is moving. When you start moving the door, the hinge lock bends and the force gets high enough from the bending for it to jump forward a bit and then it stops and bents a bit then jumps forward again in a cycle. This bending and jumping of the hinge creates a space that becomes compressed when a piece of the hinge jumps forward, causing the sound wave between 50-100 Hertz.

Yeah that is great and all, but what about how humans can create sound?

When you clap, you are actually squeezing the molecules in the air into a finite volume (your cupped hands) and shooting them out away from you. This releases pressure waves propagate out from your hand into the environment and are detected by our ears through a system of drum and fluid filled sacs connected to our nervous system.  Kinda cool right? It gets even better.

In nature some species have evolved to use sound as a means of catching prey. The Alpheidae, more commonly known as the pistol shrimp, currently holds the record for being the world loudest animal. The pistol shrimp snaps its claw that shoots water so quickly that it vaporizes the water around it into a bubble (known as a cavitation bubble). Since the pressure at the bottom of the ocean is 1000 times the pressure at sea level, the bubble gets compressed by the weight. This collapsation of the bubble causes a fraction of a second increase in temperature comparable with the surface of the sun (5,000 C).

So the next time you want to stun an enemy or impress someone with your super powers, give them a standing ovation.