Thread: Sailing
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Old 03-17-2008, 03:07 PM   #98
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Originally Posted by Joshi
Ice is exactly the same, if there is ice above the water level, it is not displacing any of the water it is floating in, and thus when it melts, it all melts, so that above the water is adding to the water it is floating in.
Correct observation but wrong conclusion. You are assuming that the volume of ice remains constant when it melts but it does not.

1. The volume of water displaced by ice is the volume of the ice that is submerged in the water.

2. Gravity acts on the ice and the displaced water identically. Llike a balance scale, the force of the ice pushing down into the water is balanced by the force of the water pushing up due to water being displaced. Because gravitational acceleration is constant, equal forces mean equal mass. Therefore the mass of the ice is equal to the mass of the water displaced.

3. Ice has a specific gravity of about 0.92. That means that 100cc of ice weighs the same as 92cc of water (92g) and thus 100cc of ice will displace 92cc of water and the other 8cc will be floating above the surface.

4. When the ice melts into water its mass stays the same as before (92g) but now it only takes up 92cc. The volume of the melted ice is the same as the volume of water displaced by the solid ice.

Conclusion: No change in displacement of water due to melting ice.

Originally Posted by Joshi
Ask a science teacher...

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