Acoustic Levitation

By Derek Teel
For Physics 212x Spring 2017
Instructor: David Newman

    Introduction :    

    As current information suggests, sound travels in a wave similar to that of a sine or cosine function. Depending on the frequency the wave gets a longer or shorter wavelength, and amplitude affects the "loudness" of the sound. Sound behaves like ocean waves, there is a constant flow of crests and troughs. The crests represent high pressure while the troughs are low pressure. But there is also something Sound wave with equal but opposing
                            wavescalled     the "node" in which the pressure doesn't             change at all. This is a critical component that     has allowed researchers to discover how to         levitate small objects using nothing but sound.     Left you will see a GIF in which there are two         opposing waves when the crests of the yellow     wave align with the troughs of the grey wave         the purple wave goes to zero and vice versa.
When the crests of both align with each other the amplitude doubles. The nodes in which pressure changes do not occur are where objects get trapped. The pressure under the nodes are higher than the downward force of gravity and thus leaving a net upward force on the object trapped in the node.
    This form of levitation has been found to be able to hold a Styrofoam ball the size of a golf ball which was about 3.6 times larger than the 14-mm wavelength used to levitate it ( This means that we aren't necessarily restricted by the
size of the object and amplitude/wavelength as previously thought.

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