There are the famous experiments, which show, how an Oxygen soap bubble gets attracted by a magnet due to it's paramagnetism. And how a Nitrogen bubble gets repelled by it (in air) But how does one calculate the attraction force of this pure Oxygen soap bubble in air due to a magnet. I'm Sorry, this isn't directly a homework. But I really want to be able to calculate this, as I found this experiment very astounding. But unfortunately I lack the ability to calculate it. I would think I have to calculate the force on one O2 molecule due to the magnet and then sum it up over the volume of the bubble with the corresponding O2 density. Then I have to subtract the O2 density of the air from it (as it wouldn't be attracted if it has the same O2 concentration), to get the total force. But how does one calculate the force on a single O2 molecules due to a magnet. And is only the magnetic (field) strength important here for the force developed or also the inhomogenity. I would expect that in a homogeneous m-field there would be no force. Thanks for any answers or hints on how to solve this problem.