What principle explains buoyant force and who formulated it?

• A. Pascal's principle
• B. Archimedes' principle; buoyant force equals the weight of displaced fluid
• C. Bernoulli's principle
• D. Newton's third law

Answer: (B)

Buoyant force is explained by Archimedes' principle: the upward push on a body immersed in a fluid equals the weight of the fluid that the body displaces. In a still fluid, pressure increases with depth, so the pressure on the bottom surface is greater than on the top. When you add up all the pressure forces, they produce a net upward force equal to the weight of the displaced fluid. This can be written as F_b = ρ_fluid g V_submerged, which shows why objects float, sink, or neutrally buoyant depending on how heavy they are relative to the displaced fluid. Other principles describe different effects in fluids—Pascal’s principle is about pressure transmission in confined fluids, Bernoulli’s principle about changes in speed and pressure in moving fluids, and Newton’s third law concerns action–reaction pairs—none capture the specific relation between displaced fluid and buoyant lift like Archimedes’ principle.