Fluids introduces density, pressure, and how forces and conservation laws apply to liquids. This unit covers density as mass per volume, pressure and how it varies with depth, buoyant force as a result of pressure differences (Archimedes' principle), and conservation laws governing fluid flow, including the continuity equation and Bernoulli's equation. Fluids connects forces and energy concepts from earlier units to a new kind of system where mass is continuously distributed rather than concentrated in objects.