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Explanation of how to create sound waves by Ron Kurtus - Succeed in Understanding Physics. Also refer to physical science, tuning fork, loudspeaker, guitar string, drum, vocal chords, kazoo, bottle, air, blowing, explosion, compression wave, vibrations, School for Champions. Copyright © Restrictions
Creating Sound Waves
by Ron Kurtus (18 February 2002)
Sound consists of compression waves in some material—usually air. Sound waves are created by the vibration of some object or even air itself. They can be created by a back-and-forth motion of an object, by having air pass over a vibrating object, or by moving air causing the vibrations.
Questions you may have include:
- How is does a vibrating object create sound?
- What is an example of sound created by air passing by a vibrating object?
- How can air cause its own vibrations?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
Useful tools: Metric-English Conversion | Scientific Calculator.
Vibration creates sound waves
Whenever an object in air vibrates, it causes compression waves in the air. These waves move away from the object as sound. There are many forms of the vibration, some not so obvious.
The back and forth movement of a loudspeaker cone, guitar string or drum head result in compression waves of sound. When you speak, your vocal cords also vibrate, creating sound.
Blowing across a bottle top can also create sound. In this case, the air inside the bottle goes in a circular motion, resulting in sound waves being formed. Wind blowing through trees can also create sound this indirect way.
Sound can also be created by vibrating an object in a liquid such as water or in a solid such as iron. A train rolling on a steel railroad track will create a sound wave that travels through the tracks. They will then vibrate, creating sound in air that you can hear, while the train may be a great distance away.
Back-and-forth vibration
A vibrating object will cause these compression waves in air or another medium.
A good example is a tuning fork. The metal rods in the tuning fork move back-and-forth, causing the compression wave in the air. A tuning fork could also be put in water, creating sound waves within the water.
Note that the waves created by the tuning fork on the surface of a pool of water are not sound waves. They are surface waves, which are circular instead of compression waves.
Other examples of something vibrating back-and-forth to cause sound are a guitar string, drum, loudspeaker.
Passing by vibrating object
If something vibrates as air passes through or by it, the air can be also made to vibrate as sound waves. The best example of that method come from your vocal chords.
The air causes some of the vibration and the vibration then amplifies the sound. You can see this by putting a thick blade of grass between your thumbs and blowing on it. Another example is wrapping a comb in wax paper, putting it up to your mouth and blowing on it to make the noise, similar to a kazoo.
Air causes its own vibration
When moving air passes an by object, it can start some air to vibrate and make sound. This type of sound can be heard on a windy day or when you blow across the top of a bottle.
One example is an explosion, which results in a sudden surge in air, causing the high-volume sound. Thunder and a balloon popping are other examples of this way of creating sound.
Summary
Sound can be created by a back-and-forth motion of an object, by having air pass over a vibrating object or by moving air causing the vibrations.
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Resources and references
The following resources provide information on this subject:
Websites
Loudspeaker Basics - From HyperPhysics
Books
Mini-quiz to check your understanding
If you got all three correct, you are on your way to becoming a Champion in Physical Science and sound. If you had problems, you had better look over the material again.
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Creating Sound Waves