Why do bubbles rise in water?

Answer 1

Bubbles are filled with air, or other gases, which are less dense than water. This causes them to rise.

This is the same reason why helium balloons rise. The helium in the balloon is less dense than the surrounding air, and the balloon thus rises.

Answer 2

Phillip J. give a link to a good description of part of what is going on. I repeat that text here:

"The pressure inside the bubble is nearly constant because the air is not very dense. Outside the bubble the pressure increases with depth because the water is pretty dense. So the outside pressure is greater on the bottom of the bubble than on the top, and that pushes the bubble upward."

This description, while accurate, misses some of the key points - key points missed by several of the other responses also.

Many of the responses focus on how the "less dense" bubbles will naturally rise in the "more dense" water. This does not explain, however, why a rubber ball buried in the sand will not rise - even though it is less dense than the sand.

So, part of the answer is that water is a fluid. It has to be fluid enough to move out of the way when the bubble is moving up.

Also, while focusing on the density and such of the "bubble" might be more relevant to a balloon or ball rising in the water, the answers miss the issue of why a bubble forms in the first place. While a ball has a definite wall - a "bubble" of air is just that, air, encased in a "bubble" of water.

A complete answer would have to include a discussion of the surface tension of the water and the chemical characteristics of the gas and the water. Just saying that the gas is lighter - would not prevent the gas from diffusing in the water and finding its way up or sideways in some form other than a bubble.

That being said, given the surface tension characteristics of water and the density of the gas - the answer referenced by Phillip J is correct - the real reason that it move up is that the gradient of pressure from the top of the bubble to the bottom in the water is steeper than the gradient of pressure from the top of the bubble to the bottom inside the bubble. The sum of the force vectors acting on the outside of the bubble with respect to the force vectors acting outward from inside the bubble - add to a net, resultant force upward.

The surface tension of the water ensures that the bubble holds its shape - although a bubble that rises from a great depth may break apart one or several times as it rises and the size of the bubble expands beyond the maximum size permitted by the surface tension of the water.

The fluidity of the water permits the bubble to rise.

I know, I know - more than you needed - so shoot me.

Answer 3

A bubble full of air has much less weight than the weight of equal volume of water, so the upward thrust on the bubble is much more than the weight of the bubble, so it rises to the surface

Answer 4

Bubbles (of air) are less dense than water, and hence float so submerged bubbles will rise. If you instead had a bubble/ball of mercury in a bottle of water it would sink because mercury is more dense than water.

Answer 5

the air in the bubbles makes them less dense than water.

Answer 6

because the gas the bubbles are made of is less dense than water

Answer 7

whatever the bubbles are filled with is less dense than the water surrounding it.

Answer 8

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Answer 9

less dense than water

Answer 10

Link below to same question asked a month ago.