Demos: 2B-13 Buoyancy
This demonstration is based on the question: What will happen to the level of water when the bricks are removed from the boat and placed into the water?
As you can see from the two pictures, the water level drops. According to Archimedes Principle, the weight of the displaced water is equal to the buoyant force on the object. In the first picture, where the bricks are floating, the buoyant force is greater and thus a larger amount of water is displaced. In the second picture, the bricks have sunk, thus the buoyant force is smaller which means a smaller amount of water is displaced. Consequently more water is displaced when the bricks are in the plastic tub compared to when the bricks are in the water. This explains the difference of the water levels.