- 1). Draw a sine wave for your audience on a whiteboard or chalk board. Point out to your audience that this is a generic mathematical description of a wave. The amplitude is one-half of the height from peak to trough, while the wavelength is the horizontal distance from one crest to the next.
- 2). Explain to your audience that sound waves transmit matter but not energy. In other words, the molecules in the medium through which the wave is passing just move back and forth -- only the wave itself actually travels.
- 3). Point out to your audience that a sound wave is a longitudinal wave. When particles in the medium move back and forth, their motion is parallel to the direction the wave is traveling. This is different from a wave on a string, where the particles in the string move up or down (perpendicular to the direction of travel of the wave).
- 4). Explain that the sine wave model also describes a sound wave, because it shows how pressure at any one given point varies over time as the sound wave travels past. It also shows how the displacement changes (i.e. how the molecules in the path of the sound wave move back and forth). The sound wave will essentially consist of alternating regions of high and low pressure.
- 5). Ask your audience to imagine for a moment that they could watch a sound wave as it passes. If they have a stopwatch, they could count how long it takes from the instant that one region of high pressure passes them to the time when the next high-pressure region passes. Explain that this length of time that just elapsed is called the period of the wave, the amount of time it takes for a single wave (from one crest to the next) to pass.
- 6). Ask your audience to think about a similar situation. Suppose that rather than measuring the length of time elapsed, they count the number of waves that pass in a given interval -- one second, for example. The number of waves that pass each second is called the frequency.
- 7). Point out to your audience that the higher the frequency -- the more sound waves pass each second -- the higher the pitch. In other words, our ears register higher frequency as higher pitch.
- 8). Draw two more sine waves, one of them very compressed with a very short wavelength and the other with a very long wavelength. Tell your audience that both graphs represent sound waves traveling through the same medium at the same speed. Ask them to identify the one that will have the higher pitch.