Standing Wave Tube
By changing the pitch of the tone, you can create a sound pattern that you can see. Though you are not actually seeing the sound wave, you are seeing how the foam balls are affected by the sound wave. The foam balls are lining up in formation due to the sound wave pattern moving through them. By measuring the distance between peaks, you can find out the wavelength of the sound wave. Sound travels as vibration waves through a substance whether that substance is air, water, metal, or anything else. Normally these waves travel in all directions from the source of the sound. If they are reflected back and forth so that the reflected wave adds to the oncoming wave, a standing wave is produced.