What makes wine glasses sing?

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"Congratulatory remarks about the wedding ... Wasn't the wedding ceremony beautiful? That row of handsome men and a parade of gorgeous attendants. And ..."

Making wine glasses sing by rubbing a wet finger along the rim has been a popular party trick for centuries. The ghostly, pure tones demonstrate several scientific phenomena.

1. Wine Glass Resonance

   • Wine glasses make musical tones when they vibrate at their natural frequency. When this occurs, the rim and sides of the glass are oscillating inward and outward like a bell. The rate a glass vibrates, also known as its frequency, is determined by its size, shape and thickness.

   The Slip-Stick Motion

   • The motion of running a wet finger along the rim results in slip-stick motion. This is when the right amount of friction causes one object to alternate between slipping over another object and sticking to it. Slip-stick motion causes a glass to vibrate when a sliding finger pushes and releases the glass repeatedly at a very fast rate, transferring energy from the motion of your finger into the glass itself. Another example of slip-stick motion would be a violin bow moving along a string. In both cases, the slip-stick motion is so fast that the movement appears to be completely smooth and uninterrupted.

   Adjusting Pitch

   • Every glass has its own natural frequency based on the physical properties of the glass, and this frequency equates to its musical pitch. The pitch can be adjusted by adding or removing water from the glass because the water absorbs the vibrations and reduces its frequency. Add water to lower the pitch and remove water to make it higher.

   Fun Fact

   • Benjamin Franklin was so captivated by the practice of making wine glasses sing that he devised a serious musical instrument called the armonica. It was built from a set of glass bells that varied in size from large to small, one for each musical note of a small piano. The bells were attached to a foot-powered spindle which rotated the glass bells. The armonica player would then apply a wet finger to a bell and cause it to ring out. At one point the armonica was so popular that Mozart and Beethoven both composed for it.

Source: www.ehow.com

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