A piece of wood is floating in a bathtub. A second piece of wood sits on top of the first piece, and does not touch the water. If the top piece is taken off and placed in the water, what happens to the water level in the tub?

Pascal's principle: If an external pressure is applied to a confined fluid, the pressure at every point within the fluid increases by that amount.
Archimedes' principle: The buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object.

Bernoulli's principle: Where the velocity of fluid is high, the pressure is low; and where the velocity is low, the pressure is high.