Why do tea kettles make noise?
Most people enjoy a hot cup of tea or coffee - or even hot chocolate. No matter what kind of hot drink you enjoy, you've probably either boiled a kettle or seen someone else boil one. And it may have struck you as odd that a kettle makes noise.
We know, of course, that the noise made by the kettle is an indication that the water is either boiled or very close to it. It's a little more complicated what actually makes the noise, however.
There are two types of noises made by kettles - although not every kettle will make both. The first type is the bubbly, boiling sound. And the second is the whistle that many older type kettles make. Both questions will be addressed below.
Why are kettles noisy?
Kettles usually make a strange steamy, bubbly noise as they begin to heat up.
The explanation for this is simple. Basically, the element at the bottom of the kettle, which heats the water, causes the noise. The water around the element heats fast and turns into steam. This steam rises and meets the cooler water at the top of the kettle. Of course steam turns back into water when cooled.
Because water is less dense than steam (takes up less space than the steam), the transformation of the steam into water leaves a space which the remaining water rushes to fill - and that's what makes the noise. The bubbles of steam get bigger and bigger as the water heats, making more and more noise.
Why do kettles whistle?
Older style 'whistle' tea kettles have a special type of lid which creates the whistle we hear when water reaches boiling point.
The spout is actually two pieces of metal, about 1/8 inch apart. As the steam builds and tries to escape the kettle, it passes through the two holes in the metal plates. In doing so it creates oscillating air pressure that turns into vibrations or sound waves - that then reach our ears.
Photo thanks to iMorpheus on Flickr