TPBLeap - Creative Futures

by JJ Vernon

Chapter 1 - What is Sound?

This is a simple question, but the answer is far from straightforward. Part of the reason for this complexity is because "sound" consists of several different processes.

It makes it easier to understand what is going on if we split this question into parts.

1. What causes sound?

Sound is produced by an object that is vibrating in air. If you consider anything that produces a sound there will be something vibrating.

Consider:

• A drum - when it is struck, the drum skin vibrates
• A guitar - the string vibrates when the string is plucked
• A person singing - their vocal chords vibrate
• A tuning fork - the metal vibrates when it is tapped

(NB This video has no audio)

• A speaker - the speaker cone is caused to vibrate by electricity.
• A clarinet - air is blown across a reed which vibrates, much in the same way that sound is produced when you blow across a blade of grass.
• A trumpet - the player vibrates their lips (blows a "raspberry") into the mouthpiece.

Sound will not be produced in a vacuum (the absence of anything.) This tells us that for sound to occur, there has to be some kind of substance (or medium) for it to travel in. This does not have to be air; sound can travel in water, metal, wood, etc. What is important is that there is something for the the sound to travel through.

2. How does sound travel?

Sound travels in waves. Let us consider a very simple type of wave - the Mexican wave.

What is happening here? The people in a stadium put their hands in the air in sequence so that just as the person next to them lowers their hands, the next person raises theirs & so on. A wave is formed, but what is the wave? It is the disturbance in the people that is the wave & it is this disturbance (not the people) that travels around the stadium. This type of a wave is known as a transverse wave because the disturbance is at right angles to the direction of the wave. (The people move up & down vertically, but the wave travels horizontally around the stadium.)

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