I was looking for information on calculating buoyancy of an upside-down cup in a bathtub... If I place a plastic cup upside-down in a bathtub and press down, the water goes up into the cup a certain distance depending on the force I press down. Does this mean that the pressure of the air in the cup is equal to the force I am pressing down with? Is there a way to calculate what the pressure of that air is depending on the force? I was doing some kitchen physics stuff with my nephew, and I just need a pointer to the proper equations or online tutorials. I found plenty of stuff for calculating buoyancy of floating cups (or floating anything) but nothing about air pressure. Thank you very much!