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a boat is travelling in a pond a man fires a cannon ball from the boat in to the pond will the level of water in the pond raise or fall or stay the same
The water level in the lake will go down a little bit. Archimedes'
principle says that an object which is floating displaces an amount of
water which weighs the same as the object. In the first case, the boat
with the cannonball pushes aside water that has the same weight as the
boat+cannonball. In the second case, the boat displaces only enough
water to keep it afloat, and the cannonball is resting on the bottom,
not floating. The cannonball then displaces only as much water as its
If the cannonball is heavier than water, then the amount of water
the cannonball displaces when it sits on the bottom is less than that
when it is responsible for when it is in the floating boat, and the
total level in the lake will go down.
You can try it yourself with a plastic or styrofoam cup (the boat), some marbles, and a pot of water.
(republished on 07/31/06)
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