A pot of boiling water?

jammieg

Have you ever watched a pot of water boil? I'll bet you have, but did you notice how the bubbles start off at the bottom in just a few spots as if there were an air leak from the bottom of the pot and they start off really big and then almost instantly reduce in size so small sometimes you can't even see them before floating to the top, isn't that odd? What's going on here, what would cause a bubble to do that, this is no ordinary bubble.

krab

The bubble is just water in the gas phase. At the point it is formed, the temperature exceeds the boiling point. But the liquid water above it is still below the boiling point. So as soon as it starts to rise, it shrinks and winks out.

jammieg

When you say it is water in the gas phase, do you mean it is oxygen and hydrogen gas broken down or just water vaporized to a gaseous form and that it is actually the ascension of the bubble that rapidly cools and this is what accounts for the rapid size shift? The reason I ask is when i put some magnets in the bottom of the pot a curious thing happened I can't explain but all the bubbles formed around the magnets, if the hottest areas give rise to the gaseous bubbles, it would seem that additional magnets would just give greater surface area and be cooler regions of the pot, I don't know about the thermal properties of standard magnets though, odd though isn't it?

Bob3141592

I think the bubbles start at irregularities in the surface of the pot, like scratches or sharp little protuberances. The magnets are likely to hold a lot of dust or other particles that can serve as nucleation sites for the bubbles. Also the magnets may be made of a material that has a coarser surface texture than the pot.