[Christ]

dime = approx .5" dia. x100 = approx 50" dia (manhole cover)

dime = .196 area x100 = 19.6" area (manhole cover) right? Wrong. 1,963.5" circ.

dime = 1.57" circ x100 = 157" circ (manhole cover).

Since area is a surface calculation, and it just seems to have scaled to 10,000 times, I'd say there's still something wrong with the analogy.

If the manhole cover had the same density as the dime, but 10,000 times the surface area, and only increased spatial dimensions by 100 times the mass, it would float.

The point is that the manhole cover wouldn't be able to float not because of scaling, but because of the difference in density between the two materials.

Buoyancy is described as the force opposing an objects weight in a fluid because of displacement of said fluid. If the object displaces a weight of fluid that is equal to it's own weight, it will float. On the whole, the object has less mass than the mass of the fluid it displaces. If a manhole cover really had 10,000 times more surface area and only 100 or even 1,000 times the weight, it would also float. Even if it had 10,000 times the surface area and 10,000 times the weight, it would still have the potential to float (provided that you could make a dime float, which I don't recall ever having seen), with the exception of breaking surface tension due strictly to sheer size.

Since surface tension relies on molecules' ability to stick together under strain, a much larger object would have more of a tendency to break surface tension because it would require a much larger group of molecules to cooperate.