All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Science
Up or down or... (Posted on 2005-07-22) Difficulty: 3 of 5
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?

No Solution Yet Submitted by nilshady    
Rating: 2.3333 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Another Solution Comment 20 of 20 |
First imagine a jar that the bottom half is filled with water with density 1.0 and the top half is filled with a light oil with density 0.5.  Now place a disk with density 0.75 in the jar.  It will position itself exactly in the middle - the lower half in the water and the upper half in the oil.

Now decant the oil.  The oil is replaced with air, but in this case the density of the air is negligible.  The disk will sink so that it is 3/4 down in the water, with only 1/4 exposed.  Also, the level of the water will rise slightly as the volume needed to hold the sum of the water and submerged portion of the disk is increased by 1/4 the volume of the disk.  However, this increase in the water's surface level will be less than the decrease in the level of the surface of the disk.  The net result is the disk sinks down relative to the jar.

Now put the lid on and pump out the air.  (Ignore the effect a vacuum has on liquids and assume the water will remain in its liquid state.)  Air has a density about 0.001275, and a vacuum has density 0.  The same scenario as above happens, just on a much smaller scale - the disk sinks slightly lower.

  Posted by Brian Smith on 2016-02-07 21:55:10
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (7)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2017 by Animus Pactum Consulting. All rights reserved. Privacy Information