Consider Archimedes' principle

Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

I do not understand why the center of buoyancy is the center of mass of the volume of the displaced fluid.

In principle it could be another point, for istance the center of mass of the object (not the displaced fluid) or maybe a point of the displaced fluid but not the center of mass.

Is there an simple way to understand why the center of buoyancy located in the center of mass of the displaced volume of fluid?


1 Answer 1


Let us suppose we remove the object and fill the space left (in the fluid) with the same fluid. Assume this portion of fluid become solid without changing its volume or density. It will be in equilibrium with the fluid. Now suppose the buoyancy force on this solidified portion is off the center of mass. This would imply non vanishing resultant force or torque and the solidified portion would not be in equilibrium. A kind of inverse argument can also be given. Suppose the center of buoyancy coincides with the center of mass of an object immersed in a fluid. Then you would never observe resultant torque (by means of rotations) on any object. And that is empirically not true.


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