Have you ever noticed the noise and vibration that happens when you boil water? When the water begins to get hot and bubbles start to form, the pot may begin to vibrate, and there will be a lot of noise. But in a few moments, as the water begins to boil vigorously, the vibrations and sound disappear, to be replaced by the popping of bubbles. What's going on? Why does the noise and vibration happen for a little while, and then stop? 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 a gas. This gas is called water vapour, and it forms bubbles in the liquid. Since these gas 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. Look at the close-up. As the vapour turns back into a liquid, with less volume, the bubbles collapse. This leaves little holes in the water, wherever there was a bubble. The surrounding liquid rushes in to fill the empty spaces where the bubbles were. This makes 'popping' noises. When enough of these bubbles are popping, water moving into these empty spaces makes the pot vibrate. Eventually 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. All that is left is the gentle sound of bubbles of water vapour being released into the air. Resources