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?

This is a problem about buoyancy--not surface tension.

The object is buoyed by the weight of the fluid it displaces. In the initial condition this is mostly the water--so much so that usually only the buoyancy by the water is considered.  But there is some buoyancy supplied by the air.  Now the air is gone, so some buoyancy is gone, and the object goes down, just a little.

Also, the water is less compressed and therefore is less dense, but that is probably insignificant.

Posted by Charlie on 2005-07-22 15:23:42