# The Lovely Velocity Problem

Omid Michaele
Last day , when i was working on two interconnected balloons , a question was kicking my brains !!! This is the explanation of the question:

First , suppose a system that composed of two spherical membranes filled with air (two balloons have different initial volumes {means that the pressure inside which balloons are different} and the air pressure is 1 a.t.m) . We connect them with hollow tube and a valve. When we open the valve , one of them shrinks and the other one expands (It depends on their pressure) . So how can we get the velocity of the flowing air between two balloons? (Consider everything but if you have reasons for not considering one of them -for example the ratio of friction in the tube- Don't consider them and just tell me the reason)

Thanks

Homework Helper
Gold Member
Last day , when i was working on two interconnected balloons , a question was kicking my brains !!! This is the explanation of the question:

First , suppose a system that composed of two spherical membranes filled with air (two balloons have different initial volumes {means that the pressure inside which balloons are different} and the air pressure is 1 a.t.m) . We connect them with hollow tube and a valve. When we open the valve , one of them shrinks and the other one expands (It depends on their pressure) . So how can we get the velocity of the flowing air between two balloons? (Consider everything but if you have reasons for not considering one of them -for example the ratio of friction in the tube- Don't consider them and just tell me the reason)

Thanks

I think this is pretty straightforward. If you know the pressures inside the two balloons you can caclulate the pressure difference on the two ends of the tube. Engineering textbooks will give you very simple equations for calculating the flow rate in simple things like tubes -- you need to know pressure difference, the dimensions of the tube and the properties of the gas you are pushing (pressure, temperature, composition). Since this is just air, you can probably find all of this online with a little googling. You will also find this kind of information from manufacturers of tubing, pumps, etc. In the old days of paper catalogs, the bigger companies would often have a little primer on this at the front of the catalog to help you design your gas-handling system.