A jar filled partially with water has an object floating in it. The jar is open. Now, if the jar is closed and a vacuum pump is used to pump the air out, what will happen to the floating object? will it rise up more or sink or ...? and why?
(In reply to depends on density
My only comment is that no air is being displaced below the object, only above and to the sides (and the forces exerted around the sides cancel out). Hence the buoyancy force of air is actually acting DOWNWARDS. Thus, with the weight (mainly) and buoyancy force (negligible) of air removed the object must rise.