Experiment & Explore
|14+||Medium||About 60 minutes|
Do you like listening to music and talking to your friends? These activities involve you listening to sounds. But what really is sound and what does it look like?
In this Experiment & Explore activity, you will discover what sound is by looking at its effects. You will also experiment with its properties, explore the patterns that different kinds of sounds make, and discover ways engineers might put this knowledge to work to solve real-world problems.
Make sure that your plastic container is big enough to be able to fit your speaker inside without it touching the sides or top.
A tone generator is a device that can produce a pure sound at a particular volume and pitch. Most sounds we hear are really many sounds of many volumes and pitches. A ‘pure’ sound is a sound of only one pitch or frequency.
Before starting this activity, you may have already known that sound is the result of vibrations that travel through the air (or liquids and solids) to our ears as longitudinal (or pressure) waves. These waves are caused by vibrating objects. When you hit a drum, you cause the velum (the stretched material) to vibrate which makes the air particles vibrate back and forth which creates a sound wave. The same is true for instruments like guitars where the strings vibrate .
You may have discovered that the reverse is also true - sound waves produced by you (or a speaker) cause the velum to vibrate. If you sprinkle grains of sand, salt, or couscous onto the drum, you can see these vibrations quite clearly. You can also see that sound is a form of energy transfer: it is able to make these grains move.
The sounds we hear are distinguished by their volume and their pitch, which you can see reflected in how the grains vibrate in response to different sounds. A larger amplitude (louder sound) makes the grains vibrate more vigorously. The greater the amplitude of the sound, the greater the energy it transfers.
The ‘highness’ or ‘lowness’ of a musical note or sound is called its pitch. Birds tweet at a high pitch. Lions roar at a lower pitch.
A longitudinal wave is a wave where the particles vibrate back and forth in the same direction as the direction in which the wave travels. Longitudinal waves have repeating areas of high pressure (compressions) and low pressure (rarefactions).
Frequency is a measure of how often something happens. With waves (e.g., sound waves), it is a measure of how many waves pass a fixed point per second. We experience the frequency of a sound as its pitch. We hear low frequency waves as low-pitched sounds and high frequency waves as high-pitched sounds.
Amplitude is a measure of the maximum distance a particle in a wave moves from its rest point. The greater the amplitude of a sound wave, the more the air particles vibrate and the louder the sound we hear.
So far, we have seen that a greater amplitude produces a louder sound and makes the grains vibrate more. But what about the frequency of the sound wave. How does it affect the grains?
A greater frequency sound wave results in a higher pitched sound. It turns out that different frequencies can make the grains vibrate in different patterns. The relationship between the frequency and the patterns produced is very complicated and is the result of standing waves. This relationship was first described by mathematician Sophie Germain.
Let's investigate these patterns in more detail.
Do you think we can put our understanding of sound to practical use? Consider these possibilities. Share your ideas at #nextengineersdiy.
Watch these videos to learn more about standing waves and how sounds of different frequencies create different patterns.
Learn about Pitch and Loudness. Then, compare Audible Frequency Ranges.
Watch how randomly distrubuted grains fall into patterns and demonstrate 2-dimensional standing waves.
Watch as Physics Girl uses physics to create cool patterns on a vibrating plate.