If you place an solid object on a fluid, is the force it applies to the fluid equal to the buoyant force? I would have thought that it applies a force equal to its own weight but that would mean that the force applied to the object by the fluid, the buoyant force, would not be equal and opposite to the force the object applies to the fluid unless it has a density equal to the fluid. This would violate Newton's 3rd Law. So does that mean the force an object applies to a fluid is equal to the buoyant force the fluid applies on it? And how would you physically explain this at the molecular level? This would be mean that as the object sinks it applies more and more force on the fluid. How does this differ from the situation where solid applies a force on a solid surface, like the ground?