Water Layer Thickness and Frequency of a Tapped Wine Glass

Abstract

Tapping the rim of a wine glass produces a tone. When water is added to the glass, the pitch decreases. The decrease in pitch is attributed to the effective addition of the mass of the liquid to the vibrating walls of the glass. A solid cylinder fixed in the center of the glass reduces the thickness of the layer of water. Chen derived a theoretical model of the effect of the thickness of the water layer touching the walls on the frequency produced, and tested its validity down to a minimum water thickness of 2 cm. 4Here, we test Chen’s model for water layer thicknesses below 2 cm. Cylinders of different diameters were inserted into the center of a cylindrical glass, while controlling the depth of the water. The sound of the tapped wine glass was recorded and the frequency determined. It was found that Chen’s model accurately predicts the frequency for water layer thicknesses above 2 cm, but increasingly diverges for thinner layers.