Fluids at Rest

Pressure

Pressure in a static fluid grows with depth, not container shape: $P = P_0 + \rho gh$ Gauge pressure leaves out the atmosphere; absolute pressure includes it. Pascal's principle transmits a pressure change undiminished, so a hydraulic lift multiplies force by the area ratio.

Buoyancy and Surface Tension

The buoyant force equals the weight of the fluid displaced, $F_b = \rho_{fluid}V_{sub}g$. An object floats when its average density is below the fluid's, and the submerged fraction equals the density ratio. Cohesion at a surface gives surface tension; adhesion to the walls drives capillary rise.

Key Takeaways

• Depth, not shape, sets static pressure.
• Buoyancy depends on the fluid displaced, not on the object's weight.