Why does bubble rise when heating?

Question

Why does bubble rise when heating?

Answer 1

Heating a bubble?  What do you mean?

Answer 2

the gas in the bubble is expanding and getting lighter

Answer 3

If you mean the bubbles appearing before the water has even reached boiling temperature, this is dissolved air coming out of solution.  The solubility of gases like nitrogen and oxygen in a liquid (like water) depends a lot on temperature and pressure.  In fact, one of the tricks for making carbonated drinks is to chill them while applying a mild carbon dioxide pressure.  We used to make rootbeer at home from rootbeer flavoring, dry ice (that's frozen carbon dioxide) and a tightly-sealed Coleman jug.  The dry ice provided the carbon dioxide and low temperature (-78 C, or -109 F).

If the water is boiling, the bubbles are vaporized water (steam).  In any case, the bubbles rise through the water because they are less dense than the liquid (as most gases are).  The pressure of the surrounding liquid above the bubble is *just* slightly less than below, so there is a net buoyant force pushing the bubble up.  Furthermore, the average pressure is less when the bubble is closer to the liquid's surface, so the gas (being under less pressure) expands as it rises -- the bubble grows bigger as it comes up.

Answer 4

Gas Build up