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 Up or down or... (Posted on 2005-07-22)
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?

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 Easy! | Comment 18 of 20 |
This is extremely easy. By using a vacuum pump to remove all the excess air, you've expanded the volume of the water to the volume of the container minus the volume of the object. It's density is now obvious, and the object's has remained the same. If the object is *still* less dense than the water, it'll be sitting right at the top of the jar. If not, it'll float relative to the new density of the water.

Open up your high school physics textbooks for the proper equations. Rho, the normal density of water, is 1000 kilograms per cubic meter. of course, this density has decreased since vacuum-pumping directly proportional to the relative increase in the water's volume.

This is assuming the jar does not implode. In which case, the object is on the floor just being wet.
 Posted by Aerik on 2006-03-14 02:11:25

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