Why does a teakettle make noise as the water approaches a boil? What determines the frequency of sound?

zbeckabee

"When you heat water on the stove, the layer at the bottom is the first to boil, meaning it turns into a gas. The water vapor collects into bubbles, which rise toward the surface, passing through cooler water en route. The lower temperature causes the vapor to recondense into liquid and the bubbles collapse, making a noise. This gets gradually louder, as bubble production increases, until the water is so uniformly hot that the bubbles make it to the top without popping. At this point the noise diminishes. But it takes a moment before the vapor pressure builds up sufficiently in the top of the kettle to make it start whistling." http://www.straightdope.com/classics/a2_115a.html Sep 26 07, 9:38 AM