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why does an egg float in salt water
The big difference between salt water and regular water is that salt
water is more dense than regular water. That means that every bit of
salt water weighs more than regular water. That makes sense because
we've added extra salt to the mix.
The next step is how things float. The easiest way to remember if
something floats is to think about how much water it displaces. So if
we take the volume of the egg and take that much water, which weighs
more? The salt water will weigh more than the egg. This means that if
the whole egg were under the surface of the water, the water will push
up on the egg more than gravity pulls down on the egg. The result of
this is that the egg gets pushed up to the surface, and will float with
a slight fraction of its volume above the level of the water. In fact,
it will float is such a way that it has displaced a volume of water
whose mass is exactly equal to the egg's mass.
Incidently, the regular water weighs less than the egg, so the egg will sink to the bottom.
(republished on 07/31/06)
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