Thursday, 22 October 2015

newtonian mechanics - How to calculate the buoyant force on a balloon at different altitudes



For a project into balloon simulation I'd like to know how the force on a balloon changes with altitude:


I know that the Buoyant force on a balloon is:


$F = (\rho_{air} - \rho_{helium})gV$


Using changing air density from the international standard atmosphere and changes in gravitational acceleration I can calculate the buoyant force and add this to the (negative) force of gravity mg.


However I know that it isn't this simple, the balloon changes volume with altitude as the air pressure outside the balloon changes.


I'd like to know how the balloon inflates - this would be a great help!



I think it may be something to do with ideal gas laws - I can calculate air temperature and pressure from the international standard atmosphere but do I use pressure as the air pressure? - or air pressure minus balloon pressure?




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