Good, good, good vibrations
Sound is actually nothing more than moving air and the way we perceive that moving air with our ears. Now you may be saying “Wait a minute Geek Slop… sound is made by moving air?”. Sure. Think about it. Your dad moves a lot of air – right? And he makes a nasty sound when he moves it – yes? Let Geek Slop explain…
- Cut off a piece of two foot string (2′).
- Using a rubber band, attach a metal spoon to the midpoint of the string.
- Wrap the ends of the string around your fingers.
- Rest your fingers in your ears (don’t stick ’em in too far or you’ll poke your brains out!).
- Standing next to a table, rock your body back and forth so that the spoon taps against the side of the table.
What do you hear? When the metal spoon taps against the table, it sends a vibration up the string, through your fingers, and into your ears. Your eardrums pick up the vibrations and send them to your brain where they are translated into what the brain perceives as sound.
Everything around is is matter and all matter is made of molecules. The molecules in matter can be packed at different densities. Molecules in a solid are packed together more tightly while molecules in a liquid or gas are packed together more loosely. When energy, such as the moving air that makes sound, strikes the molecules in matter, it causes the molecules to vibrate back and forth which produces a wave of sound energy. If the molecules are packed together closely, the sound can be transmitted easier. In a solid, where the molecules are packed together tight, the vibrating molecules do not have to move very far and hence, the sound travels faster. Solids are excellent transmitters of sound. Steel can transmit sound at 5,200 meters per second vs. 340 meters per second when traveling through the air. This explains why putting your ear to a railroad track, although very dangerous and stupid, lets you hear the train much further away than simply listening for the train sound coming through the air.
By the way, sound travels faster through hotter objects too.
Supplies: Rubber Band, String, Spoon