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?

Larry din't talk about upward forces in the floating object.  It is equal to liquid pressure at the bottom of floating object plus the atmospheric pressure. 

So the atmospheric presure cancels out.

As you pump air out, the apparant weight of floating object increases, however slightly- so it will go down slightly.  Less its density, more it will go down.

As to boiling, it won't last after reaching saturated pressure.  The vapour density will still be small. 

Posted by ravi on 2005-07-23 10:56:24