Mechanical Energy-Sound•Science of Boomwhackers.

BACKGROUND:

Boomwhackers create distinct tones when whacked against a surface. The tone is determined by the length of the tube. The tubes are cut to the correct lengths to form the eight notes in a C major diatonic scale (C-D-E-F-G-A-B-C).

The tubes create tones in much the same way as other tube-shaped instruments. They filter a particular tone from noise that is introduced into the tube. A clarinet is played by vibrating a reed at one end. The reed does not vibrate at any particular frequency, but produces a range of frequencies (a buzzing noise). The shape of the clarinet and which holes are covered determine which frequency is amplified. Boomwhackers work in much the same way. Whacking the tube produces a noisy sound that contains many frequencies. The tube, because of its length, resonates and amplifies one of the frequencies. Notice, in the figures below, that the resonant wavelength is one that has antinodes at both ends of the tube.

EXPERIMENTS:

1. Pitch/Wavelength: Whack two different tubes. Which tube produces the lower tone? How do the lengths of the tubes compare? Longer tubes produce lower tones because they amplify a longer wavelength (lower frequency).