In this problem set I have a passage that describes an experiment that looks at the changing temperature as an air filled balloon rises to the surface from the bottom of a water filled tank. The graph they provide shows that as the balloon rises to the surface the temperature of the air in the balloon decreases. (I'm paraphrasing a lot of the question because it's long and has a bunch of information that's not pertinent such as dimensions of the tank, dimensions of a valve that's not even used in any problem!!! etc.)
I'm struggling with the idea of the temperature changing at all. From the answers from the problems it seems that the gas is doing work by expanding thereby losing internal energy and thus temperature. This to me makes sense, but I keep looking at the PV=nRT and thinking well wait, wouldn't the temperature just be fixed and the volume and pressure change correspondingly? Help getting through these basic concepts would be great!
Also one of the problems I struggled with:
Which of the following items of information would NOT help in predicting the results [shown in the graph]?
A) The number of air molecules inside the balloon
B) The thermal conductivity of the rubber (of the balloon)
C) The variation with depth in the speed of the balloon
D) The total mass of the water in the tank
Answer is D
I'm confused what the test makers were hinting at with C; if C could be included in your explanation of this experiment that would be great (does this somehow give the amount of internal energy lost??). I can't find other examples of this kind of experiment, is it a specific type? I.e. Does it have practical applications (even a name of like a standardized experiment similar to "pendulum motion" etc) or is it simply a conceptual check?