Fluids

Fluids -- liquids and gases together -- are found everywhere: roughly two-thirds of the Earth's surface is covered by water, and the atmosphere of air envelops the whole planet. Unlike a solid, a fluid has no defined shape of its own. Within this broad category, a liquid still has a fixed volume (it takes the shape of whatever part of a container it occupies but does not expand to fill the whole container), while a gas has neither a fixed shape nor a fixed volume -- it always expands to fill the entire volume available to it. This section develops the physics of fluids AT REST: how pressure is defined and measured, how density and relative density describe a fluid's material, how pressure builds up with depth in a static fluid column, Pascal's law for transmitting pressure through an enclosed fluid, and buoyancy -- the upward force a fluid exerts on anythi …