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Originally Posted by Yankee
I asked the question because I was curious about the answers that I’d get. Let me give you a brief high school level primer:
Specific gravity also known as relative density is the ratio of of an objects density (mass/volume) to a reference density, which is usually water but also can be a gas or any other form of matter. It has absolutely nothing to do with the weight of an object, in this case the aforementioned rock.
Weight is the force enacted upon a body (of a certain mass) when exposed to a gravitational field. This is why a person would weigh less on the moon than the Earth, but he would also maintain his same mass. It’s suffice to say, whether the rock is under or above the water, it will have the same mass and since the Earth’s gravitational field is constant, it will have the same weight. So it will be just as heavy no matter where on the Earth that it resides.
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OK, what would happen if we were to hang the rock on a scale while it's in the water and while it's out? Would the scale read the same weight or not? That was my point. I realize the rock's mass never changed.