Sound - Part 2

What is sound and how does it work? This two part visit will cover what sound is and how it travels. We'll do some activities to create sound and test how it travels through different mediums. We'll also make our own instruments and learn about pitch in both wind and string instruments.

How to musical instruments make sound?

Sound is created whenever air vibrates. This happens when you speak - your breath pushes the air, causing it to bunch up and compress. The air gets compressed and stretched in a longitudinal or sound wave.

Anything that vibrates will vibrate the air around it and make a sound. In wind instruments like a flute, you use your breath to vibrate the air. In string instruments, you pluck the string and make it vibrate, which vibrates the air around the string. In precussion instruments, you hit something and caure it to vibrate, which vibrates the air around the instrument (drum or cymbal).

What is pitch and what is loudness?

Waves have two main properties: wavelength and amplitude. The wavelength is how long the wave is and the amplitude is how bit the wave it.


Wavelenth (top) describes how long a wave is, and amplitude (bottom) describes how big a wave it. (Credit: Mr Clintberg's Studyphysics)

Sound waves are longitudinal waves, so they look more like this:



Wavelenth of a longitudinal wave (Credit: Mr Clintberg's Studyphysics)

The wavelength (how long the wave is) defines the pitch of sound, and the amplitude (how big the wave is) defines the loundess.


Short wavelength = high pitched (squeeky sound), long wavelength = low pitch (deep sound) (Credit: Wired@School)




Big amplitude = loud sound (more energy, travels farther), small amplitude = soft sound (low energy, doesn't travel far) (Credit: Wired@School)

Activity 1: Making sound with nails. Get three thick nails of different lengths and, using a drum stick, bang on each nail in turn. Which do you think will have the higher pitch? (link)

Activity 2: Get a bunch of empty bottles (preferably the same size and shape) and fill them with different amounts of water. Either blow over them or simply hit them with a soft drum stick. Which make the higher pitch - those wth more or less water? (link)

(A good text to help you learn about sound is "Sound and Vibrations" by Gerard Cheshire (2006), part of the Science Essentials: Physics series)

Last updated: Thursday, 03-May-2012 23:00:34 AEST
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