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Q & A: What is Sound?

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Most recent answer: 07/25/2011
What are the sound characteristics? Were does the sound came from?
- Diana Freire (age 13)
Salesianos de Manique, Cascais, Lisboa, Portugal
Sound is a type of wave. Another example of a wave would be a water wave traveling in the ocean. As the wave comes by the water raises up and then lowers down. The water in the wave is called the medium. A medium is what scientists call the thing that waves move through.

Another example of a wave is the waves people make in a stadium. As the wave comes by the person stands up and sits back down. Notice that the people don't move around the stadium, they only move up and down, but the wave does move around the stadium.

Getting back to sound, sound is a wave of pressure that can travel in gasses, liquids or solids. The crests of the wave, which are correspond to the high points on a water wave, are areas of high pressure. The troughs, which are like the low spots on a water wave, are areas of low pressure. Sound is created by a vibration. If you hum a note and press your hand agains your throat you will notice your throat is vibrating. This is your voice box wiggling back and forth making the waves of pressure. You might notice that the higher the pitch note you hum the faster your throat seems to vibrate. These waves of pressure travel through the air and then wiggle the ear drum of the listener. Your ear is designed to detect these wiggles in the ear drum and that is how you can hear.

How fast sound moves is determined by the medium it is traveling in. In general, sound travels faster in materials that are hard to compress and not very dense, and slower in materials that are easy to compress and very dense. Steel is much harder to compress than air, but also much more dense, so the two factors partly cancel. It ends up that sound travels twice as fast in steel as in air.
Unlike light waves, sound needs to have atoms there to travel. In space, where there are not many atoms to pass along the wiggles sound cannot travel (contrary to what you might see in the movies with things blowing up loudly in space).


(published on 10/22/2007)

Follow-Up #1: What is a sound wave?

What is sound wave? How do you stop sound?
- akash (age 8)
Akash- I've combined your two questions and listed them as a follow-up to a similar old question.

Sound in air is a wave with regions where the air is a little more dense and regions where it's a little less dense than average. The waves move around sort of like the ripples you see on a pool of water.

The sound waves can be stopped if they hit something like a very hard wall that doesn't move much when the air pressure on it changes.

Mike W.

(published on 07/25/2011)

Follow-up on this answer.