Latest post of the previous page:
Hi y’allI’ve just asked the wife, who used to be a microbiologist and knows about these things.
According to her, the noise is not caused by the water but by the kettle vibrating. When the water begins to get hot and bubbles start to form, the kettle begins to vibrate; hence the noise. But as the water begins to boil vigorously, the vibrations and sound disappear, to be replaced by the sound of boiling water.
This is because, as the water is heated, the bottom layer of water gets hot enough (100° C) to begin turning some of the water from a liquid to vapour, which forms bubbles in the liquid. Since these bubbles are less dense than the water around them, they begin to rise. At this point, however, the top layer of the water is still cool. When the water vapour bubbles rise into this cool layer, they are cooled enough so that the vapour condenses back into a liquid. The bubbles collapse. This leaves little holes in the water, into which the surrounding liquid rushes in to fill the empty spaces where the bubbles were. The movement of water into these empty spaces makes the pot vibrate.
Eventually, however, the upper layer of water reaches 100° C also. When that happens, the bubbles forming on the bottom can make it all the way to the top of the pot without condensing back into a liquid. So the noise and vibration stops, to be replaced by the sound of bubbles of water vapour being released into the air (i.e. the kettle boiling).
I’ll let her go back to sleep now, shall I?