Physics for the MCAT: Chapter 4 – Fluids

Chapter 4.1: Characteristics of Fluids

• Definition of Fluids: Substances that can flow, including gases and liquids.
• Weakness to Shear Forces: Fluids are weak to shear forces (tangential forces).
• Density (ρ):
  • Formula: ρ = mass/volume
  • SI Units: kg/m³, commonly g/cm³.
• Weight of a Fluid:
  • Formula: weight = ρ x volume x gravitational acceleration.
• Specific Gravity: Density of a substance compared to the density of water (1 g/cm³).
• Pressure:
  • Formula: Pressure = Force/Area
  • Units: Pascals (Pa)
  • Conversion: Important for MCAT (e.g., Pascal to atm).
• Absolute Pressure: Pressure exerted on an object at any given moment.
• Atmospheric Pressure: Varies with altitude.
• Hydrostatic Pressure:
  • Formula: P = P₀ + ρgh
  • Context: Pressure exerted by a fluid at a given depth.
• Gauge Pressure: Difference between absolute pressure and atmospheric pressure.

Chapter 4.2: Hydrostatics

• Pascal's Principle:
  • Applies to incompressible fluids.
  • Explains hydraulic systems: Pressure applied at one point is transmitted to another point.
• Work and Volume Displacement:
  • Volume = Area x Distance.
  • Work = Force x Distance or Pressure x Change in Volume.
• Archimedes' Principle:
  • Buoyant force equals the weight of the fluid displaced by the object.
  • Floating: Buoyant force = Gravitational force.
• Cohesion and Adhesion:
  • High cohesion: Convex meniscus.
  • High adhesion: Concave meniscus.

Chapter 4.3: Fluid Dynamics

• Viscosity (η):
  • Resistance to flow, measured in Pascal-seconds.
  • High viscosity: Slower flow (e.g., honey).
• Types of Flow:
  • Laminar Flow: Orderly and predictable.
  • Turbulent Flow: Chaotic and unpredictable.
• Poiseuille's Law:
  • Relates flow rate (Q) with radius, pressure difference, viscosity, and length.
  • Note: Radius strongly affects flow rate.
• Turbulent Flow:
  • Occurs at high velocities.
  • Critical speed equation relates speed to fluid properties and pipe dimensions.
• Streamlines:
  • Tracks individual particle paths.
  • Flow rate (Q) is consistent throughout the pipe: Q = velocity x area.
• Bernoulli's Equation:
  • Relationship between dynamic pressure, static pressure, and height.
  • Dynamic pressure: ½ρv².
  • Static pressure: P + ρgh.
• Venturi Flow Meter:
  • Demonstrates Bernoulli's principle: Change in pressure relates to change in velocity.
  • Slower fluid movement correlates with higher pressure.

Chapter 4.4: Fluids in Physiology

• Applications: Circulatory and respiratory systems.
• Concepts: Use of fluid dynamics principles to understand physiological processes in closed loops.

These notes summarize the key points covered in Chapter 4 of the "Physics for the MCAT" textbook, focusing on the behavior and characteristics of fluids. They will be useful for understanding fluid dynamics as applied to both physics problems and physiological contexts.