How does a buoyancy test determine the fairness of a 6-sided die?

Question

There are a lot of pages and vids out there suggesting that floating dice allows you to tell if they’re fair or not. How does this work?

In: 1

Answer 1

Buoyant forces pass through the center of volume of a body in water (so, in a die, the geometric center). However, *gravity* passes through the center of *mass* of the body. If those two points aren’t the same point, the object will reorient itself in the water so that the center of mass is directly underneath the center of buoyancy.

This is used as a test entirely because the method for loading a 6-sided die to make it unfair is to shift the center of mass towards a particular face, which makes that die more likely to roll with the opposite face on top.