I’m sitting in a boat in a pool. In the boat with me is a cannonball. What happens to the level of the pool if I take the cannonball out of the boat and drop it into the pool? Does the level increase, decrease or stay the same?

I assume that the canon ball is denser than water since I haven't seen one that isn't. The water level will go down. A floating object displaces it mass in water when a sinking object displaces its volume. Since water is less dense than the canon ball, it has more volume for the same mass. So more water is displaced when the canon ball is in the boat then when the canon ball is at the bottom of the pool. This causes the drop in the water level.

Posted by Jon on 2003-04-11 06:26:41