Darren New wrote:
> You are sitting in a canoe, in a swimming pool, holding a cannon ball in 
> your lap. You throw the cannonball overboard, and it sinks to the 
> bottom. Does the level of water in the pool go up, go down, or stay the 
> same?
> 
> (I've asked this of probably a dozen or more scuba dive instructors, and 
> only one has gotten it right. The reasoning behind the correct answer is 
> obvious once you hear it. I don't remember if I got it right when I 
> heard it.)

It goes down as measured against the edge of the pool.  While in the 
canoe, the cannonball displaces its mass in water, but in the water it 
displaces only its volume.  Since the cannonball is denser than water, 
it displaces more while in the canoe than in the water.  Since there is 
less displaced water, the water level of the pool goes down.

Regards,
John

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