Date: Around 1993
If a block of wood floats in a pail of water with weight sitting
on top of it, the waterline say is at the halfway point of the wood block. If
we hand the weight from below the block -- into the water, will the water
level on the block stay the same, increase, or go down.
You are correct that the water displaced should remain the same,
and therefore the water level on the block should go down. (since the weight
is displacing a little bit of water itself). This should be easy to test
though - how about doing the experiment to check it?
If you hang the weight below the block, the water level will no
longer reach exactly halfway up the block, but will reach slightly less than
halfway up depending on the density of the weight. It is correct to say that
the weight supported by the buoyant force is the same whether the weight is on
top, or below, the block. Also, the water displaced is the same in both
cases. The difference is that the weight displaces water when it is hung
under the block, but not when it is placed on top.
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Update: June 2012