What does "buoyancy" refer to?

Buoyancy refers specifically to the upward force exerted by a fluid on an object that is immersed in it. This force is what allows objects to float or rise when placed in a fluid, such as water or air. The concept is rooted in the principles of fluid mechanics and is described by Archimedes' principle, which states that the upward buoyant force that is exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces.

The other options do not accurately capture the essence of buoyancy. The weight of an object in air relates to its gravitational pull and does not involve any interaction with a fluid that causes buoyancy. The downward force on an object typically refers to gravity acting on the object and does not encompass the upward fluid force present in buoyancy. Lastly, the total weight of a submerged object pertains to its mass and does not reflect the concept of buoyancy, which focuses on the interaction between the object and the fluid rather than the object's own weight. Thus, the correct definition of buoyancy is indeed the upward force by a fluid.