Fluids — High-Yield Physics for MCAT

Density: ρ = m/V (kg/m³). Water = 1000 kg/m³ = 1 g/mL

Pressure: P = F/A. Units: Pascal (Pa = N/m²), atm, mmHg

Gauge pressure = absolute pressure − atmospheric pressure

Hydrostatic pressure: P = ρgh

Pressure increases with depth; acts equally in all directions

Buoyancy (Archimedes' principle):

F_buoyant = ρ_fluid × V_displaced × g

Object floats if ρ_object < ρ_fluid

Continuity equation (flow conservation):

A₁v₁ = A₂v₂

Narrower tube = faster flow

Bernoulli's equation:

P + ½ρv² + ρgh = constant

Faster flow = lower pressure (explains airplane lift, venturi effect)

Poiseuille's Law (viscous flow):

Q = πr⁴ΔP / (8ηL)

Flow is proportional to r⁴ — small change in radius = huge change in flow. Clinically: atherosclerosis reduces vessel radius → dramatically reduces blood flow.

Reference:

Wikipedia: Fluid Mechanics

https://en.wikipedia.org/wiki/Fluid_mechanics