Like surfers shooting a gnarly curl, sound travels via waves. And, just as many a surfer moves better on the water than he does on land, sound moves better through some mediums than others. Using this simple experiment, you can help students gain a better understanding of the effect these medium have on sound waves.
Easier Than Falling Off A Log
If you’re a schoolteacher, you almost certainly have everything you need for this demo already. All it takes is a wooden table or desk, at least one finger, and at least one ear that works. Most of your students probably have all this equipment, as well, so they can conduct the experiment themselves without even leaving their seats. Huzzah! Have the little buggers follow these steps—feel free to simplify or elaborate as you see fit.
First, tap ye olde finger on your table or desk. It will, of course, make a sound—if you do it right, it should sound like tapping. The harder you tap, the louder it will be, but for the sake of the experiment, try to maintain the same tapping hardness throughout.
Next, press an ear against the surface of the table or desk. With your finger about a foot away, tap again. It’s way much louder now, yes? But why?
The Sound of Science (or is it The Science of Sound?)
Sound waves can travel through most solid materials, including the wooden top of a table or desk. Most solids transfer sound waves better than air does, because the molecules in a solid are much, much more closely packed than the molecules in a gas (i.e., air). The more closely packed the molecules, the better sound waves can move through them; better wave movement equals a louder sound.
You can do this experiment a few other, potentially more interesting ways, as well. Place an inflated balloon against your ear and tap on it. Or, place one end of a wooden yardstick against a ticking clock and the other end against your ear.
In the balloon version, the air inside the balloon is more tightly compressed (and the molecules are therefore more closely packed), which makes it a better sound conductor than the freely-moving air around the balloon. In the yardstick version, the wooden material makes a better conductor of sound than air.
- 365 Simple Science Experiments with Everyday Materials, E. Richard Churchill, Louis V. Loeschnig, Muriel Mandell, and Frances Zweifel, 1997. ISBN 978-1884822674