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?
Normaly, It would be impossible to pump all the air out but if you theoretically did, (assuming that the jar doesn't shrink) you woould be forcing the water to occupy a large space thus turning it into water vapor. (similarly, if you add pressure to a tank of propane (vapor), it turns into liquid due to pressure
So if it turns into gas, the object will no longer float.
But thinking more logically, If the object floats in water, that would mean that there is either air trapped in the object or the object is less dense than the water.
If there is air, the vacume would remove it, thus epanding (more space between the particals) the object at the same rate as the water.
So assuming that the object remains intact (not epanded to the point that the molucules separate), the object will stay in the same position and neither rise or fall.