When we boil the water in the pan, first the bottom part of the water becomes hot and becomes steam. The top layer gets hot later. The steam at the bottom does not make it to the surface of the water and cools down. The upper cooler part of the water cools it and condenses it back to its liquid form. These bubbles that are formed at the bottom part lose energy when they cool down and collapse. This process is known as ‘cavitation’. When the bubbles collapse, they make a noise. As the pan heats up, the bubbles get bigger and bigger and start collapsing harder. Hence, the sound gets louder. Finally, they are hot enough to reach the surface of the water and get quiet.
Why is water loudest just before it boils?
