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? What do you think of the following approach : Normally, It would be impossible to pump all the air out but if you theoretically did, (assuming that the jar doesn't shrink) you would be forcing the water to occupy a large space thus turning it into water vapour. (similarly, if you add pressure to a tank of propane (vapour), 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 vacuum would remove it, thus expanding (more space between the particles) the object at the same rate as the water. So assuming that the object remains intact (not expanded to the point that the molecules separate), the object will stay in the same position and neither rise or fall.