Want to move a small raft? There are many ways this can be accomplished, but one of the most interesting may be through the use of sound. In Fig. 1 three plastic soda bottles are seen resting on a Styrofoam raft, which in turn is floating in a tray of water. An amplifier/speaker system located behind the tray is connected to an iPad. Using Tone Generator, a readily available free computer application from iTunes, the iPad can be used as a function generator. When the tone produced by the iPad matches the resonant frequency of the bottles, the raft will begin moving.

How did I come up with this? Like many of my projects, the idea was based on the work of others. I stumbled onto a wonderful YouTube video by Steven Dufresne at RimstarOrg entitled “Moving Things With Sound/Acoustic Propulsion.”1 In this video, plastic soda bottles are attached...

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