# Thread: Help me calculate speed of air rising underwater. Please!

1. I'm trying to find some sort of equation or any way to figure this out.. I want to be able to find the upward acceleration speed of any certain amount/density/temperature of air rising under water of any certain amount/density/temperature.

Please help! I know about buoyancy and how to calculate the amount of the upward force, that the upward force is determined by the amount of water that is being displaced.. but i dont know how to determine how fast that amount of air will rise!

Help help Help!

2.

3. well. you'll need to know the density of water. you gotta know the gass, and what form it takes when rising up. Does it stay a bubble or does it form a reversed drop of water.

without the resistances the air would travel

(9,8m/s/s * mass of the water / mass of the air)^pressure of the water.

or at least something like that (all i could think off)

i would say with resistance it would take air like 1,5 seconds to gain 2 meters upwards. i guess this way you can determine it's resistance..

4. 9,8m/s/s * mass of the water / mass of the air)^pressure of the water.
is not a vlid physical formula. what u get in the end is not m/s

5. i know, i was just thinkin about a formula (besides i hate formula's, i want to know what is on what place, and not a letter)

still, can you think of anything better?

6. Im pretty sure that this would have to be modeled by a system of differential equations. The rising gas will have a resistive force on it, which may cause the bubble to break up. These new bubbles will have a different resistive force on them, which may cause them to split up or come back together. There is just to much going on to be modeled by a simple equation.

7. i tried this problem when i were younger but for air/helium instant
i found that the differens in density tells u how much lift power it has
F=(p1-p2)*V
where p1 = 1000kg/m³ for water
and p2 = 1,3 kg/m³ for air i think.
and if we assume a bubble is a perfect sphere the viscosity force is about
F=viscosity of water * radius * velocity
or something about this, this formula isnt like this i thiink, look for viscosity and sphere on google.
those 2 forces must be equal when it reaches its max velocity and then u just solv it

8. But the problem is that water bubbles are not perfect spheres, which means that there is no easy way to find a solution.

9. i know, thats why i said "if we assume"

10. it will chose path of least resistance, should be a computer program able to work it out right?

11. the shape with least resistence, is the resistence of a rain drop

12. benonthego:
I don't know the answer to your question or how to approach the problem, whereas, I do know that the subject of bubbles of gas surrounded by a membrane or liquid environment, is a very complex issue; especially when the bubbles are oscillating and the surrounding pressure of the environment is constantly changing.

13. Originally Posted by Zelos
the shape with least resistence, is the resistence of a rain drop
a rain drop changes during it's path towards earth..

14. ure right, it changes to the shape of a rain drop. when it falls it looks for the shape with least resistence, and thats the one

15. The best way to approach this problem is probably just jump in a pool and time bubbles on their way up.

16. i've also seen bubbles making a rotating motion in a circle, like what would happen during an atomic explosion (mushroom)

only more harmless...

17.

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