Previous Post > > No, because the weight of the cannonball is already sitting on the surface of the water before it's dropped. > > I watch Mythbusters, dammit.

Okay, the situation involved a man in a boat floating in a pool, and he drops a cannonball over the side into the water. The question was whether the water level of the pool would change as a result.

The answer is: Yes, the water level should get lower.

While supported by the boat, the cannonball is displacing an amount of water equal to its mass. However, once sunk into the water, it is only displacing an amount of water equal to its volume. 

Since this isn't a trick question, we can safely assume that the cannonball is made of something significantly more dense than water... hence less water is displaced once it is sunk, and the water levels of the pool go down.


My first reaction upon hearing this question was the same as the rest of the people here, in thinking it didn't change.