AP Night Lecture #8: Fluid Mechanics

Online Video Lessons:

For animated lessons with narration and problems, visit HippoCampus's AP Physics B II website and scroll down to the "Fluid Mechanics" topics.

  1. Hydrostatic pressure
    1. Fluids are anything that can flow: liquids or gases
    2. Density (ρ) is mass/volume and in kg/m3; air=1.29 kg/m3; water=1000 kg/m3
    3. Pressure is force/area and in pascals (Pa = N/m2)
    4. Pressure of a static fluid (P) depends only on the pressure on top of that fluid (P0; often 1 atmosphere) and the depth (h) of the fluid: P=P0+ ρgh
    5. Gauge pressure is absolute pressure (P=pressure measured in a vacuum) minus atmospheric pressure (P0), so in the above equation Gauge Pressure = P - P0 = ρgh
  2. Fluid flow continuity
    1. Pipe flow rate is the volume of fluid passing per unit time, or equivalently the product of the pipe cross-sectional area the the speed of the fluid: Av
    2. Liquids are incompressible, so the flow rate is constant: A1v1=A2v2
  3. Buoyancy and Archimedes' principle
    1. Objects in fluids experience upward buoyant forces equal to the weight of the displaced fluid: Fbuoy=ρVg
  4. Bernoulli's equation
    1. Pressure (P), speed (v), and height (y) in a steady-flowing non-viscous incompressible fluid are related by: P1 + ρgy1 + ½ρv12=P2 + ρgy2 + ½ρv22
    2. This implies that as the pressure falls around an object at a given height, the fluid speed increases, or that as a fluid's speed increases its pressure will fall

Return to Lecture Index


AP Night Lectures