Archimedes' Principle states that when an object is submerged in a fluid, it experiences an upward force equal to the weight of the fluid it displaces. This means that if you place a ball in a bathtub, the water level rises because the ball pushes some of the water out of the way. The heavier the ball, the more water it displaces, and the greater the upward force acting on it. This principle explains why some objects float while others sink. For example, a boat floats because it displaces a volume of water equal to its weight, while a rock sinks because it displaces less water than its own weight.