What is the main principle behind Archimedes' principle?

The main principle behind Archimedes' principle is that an object submerged in a fluid experiences an upward force, known as the buoyant force, which is equal to the weight of the fluid that the object displaces. This principle helps explain why objects float or sink in fluids. When an object is placed in a fluid, it pushes aside (displaces) a volume of fluid. The fluid responds to this displacement by exerting an upward force on the object. If this buoyant force is greater than the weight of the object, the object will rise; if it is less, the object will sink.

This principle is crucial in various applications, including ship design and understanding why certain objects, like a balloon, can float in air. By understanding the relationship between weight and the displaced fluid, one can predict how objects behave in different fluid environments.

The other choices reference important concepts in physics but do not relate specifically to Archimedes' principle. The notion of motion and external forces pertains to Newton's first law, while the second law involves mass and acceleration, and the concept of pressure distribution is a principle related to Pascal's law rather than Archimedes' principle.