Bubbles question.....?

Aurther Hugh

Question- do bubbles in water get bigger as they rise to the surface or smaller ??? Does the same principal apply to soap bubbles ??

dgarrad

I'm not entirely sure, but I'd imagine they get bigger as they rise due to the pressure decreasing. The deeper the bubble is the more pressurised the air would be, and would therefore occupy a smaller volume. This volume would increase as the surrounding water pressure decreased.
Well I think that's right anyway! :dunno:

dudara

If you consider it just in terms of pressure, then there would be less pressure under the waters surface than at the bottom, so the bubbles would expand as they rose.

However for a more complete description, you would need to include variables such as temperatures as well. A good first approximation would to use the ideal gas law for the bubble.

In the ideal gas law, the ratio PV/T remains constant. So if T stays the same, and pressure decreases, then V must increase. However, if you allow T to change as well, then it's a little trickier to say what the outcome will be.

Capt'n Midnight

The divers forum members should be able to confirm that dir bubbles 10m down are half the size they would be on the surface , (20m =1/4, 80m =1/8 etc.)

Soap bubbles in air - the external air does not change pressure, but I'll a feeling the bubble will shrink since the air inside is under pressure from the surface tension of the soapy water and I'd reckon there would be gas exchange accross the membrane. A bit like the way a ballon goes down after a couple of days.

Soap bubbles might not shrink as fast if filled with uranium hexafluoride (then again it's probably water soluble so you'd have to use oil or something.)

PV=nRT - n is amount of gas (moles) R is constant

IIRC one mole of a gas is 22.4Litres at sea level at zero degrees C.

Tree

soap bubbles in air will die no matter what ya put in em.

look at the bubble as being a surface on the outside, a surface on the inside and a wall of liquid in the middle, the liquid will fall down due to gravity so your nice initially parralel ish walls get narrower towards the top of the bubble til POP!

its how you can tell a buble will die too, as the bubble top gets thinner it diffracts light less and gets darker, when its dark its gonna pop. MAGIC!

Capt'n Midnight

You can get special bubble stuff - it extremely viscous and the liquid sets after a while so the the bubble ends up at a more or less fixed size..