Re: Buoyancy on a submerged block on bottom of tank idiots

From: PD (pdraper_at_yahoo.com)
Date: 02/08/05 

Date: 8 Feb 2005 09:22:40 -0800

tj Frazir wrote:
> My BLOCK is 20 feet tall with a lift more thann a vaccume will hold
back
> .
> THE BLOCK has lift if its moving or not.
> I got rid of the bottom and the 20 foot tall square foot block still
> floats up.
> IDIOTS

Not a matter if it's moving.
If there is water under it, and the difference between the force
exerted by water pressure on the top and bottom of the blocks is
greater than the weight of the block, then it will float upward.
If there is no water under it -- none -- then there is no force upward
due to water acting on the bottom surface of the block. In this case,
there are three forces in the vertical direction:
1. The force of gravity acting on the block -- down.
2. The weight of all the fluid (water and air) sitting on top of the
block -- down.
3. The contact force of the aquarium pushing up exactly what it needs
to keep the block from penetrating the floor -- up.
That's it. There are no more.

It's wonderful how a simple example like this can uncover so many
misconceptions and half-understood principles.

PD

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