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c4os

Buoyancy - jar of air vs. jar of nothing

Hmm buoyancy is the topic, so let's try this. Have a look at the density of the jars in total and compare it to the density of the water. A near to perfect vacuum is quite free of matter therefore nearly no mass. The jar itself has quite a mass and is the leading factor for our estimation here: Since the air filled jar is floating the jars are big enough, so that the density difference of the air is bigger than the one of the jar's material.

Now let's assume we got lead glas (so quite the heavy sort) and 0.5 mm wall thickness, the jar shall be modelled as a cylinder with the same height as the diameter. Let's put this into some calculator:
http://www.wolframalpha.com/input/?i=solve%282.9*2*%28x-1%29*%28pi*x^2+-+pi*+%28x-0.5%29+^2+%29+%3C%3D+1.0*2*pi*%28x-1%29*x^2%2C+x%3E0%2C+for+x%29
For our example: When the glass is more than about 5.2 cm in diameter (and height) it will float to the surface.

Hope that answers it...

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