fluids

Chapter 9: Fluids

9.1 States of Matter

  • Fluids Defined: Includes both liquids and gases; they are easily deformed by external forces.

  • Liquid Properties: Flows and takes the shape of the container; generally treated as incompressible (fixed volume).

  • Gas Properties: Expands to fill its container and can easily be compressed.

9.2 Pressure

  • Microscopic Origin: In a static fluid, atoms or molecules are in motion, causing fluid pressure through collisions.

  • Static Fluid: Assumed not flowing; any solid in contact is at rest.

  • Fluid Dynamics: The movement of fluids contributes to different pressure levels based on the fluid state and environment.

9.3 Pascal’s Principle

  • Concept: In a static fluid, pressure changes at any point are transmitted throughout the fluid uniformly.

  • Applications: Underpins mechanisms like hydraulic lifts and brakes.

9.4 The Effect of Gravity

  • Density: Defined as mass per unit volume; represented by rho (ρ).

  • Pressure Variation with Depth: Explores how pressure increases with the depth of fluid due to gravity.

9.5 Measuring Pressure

  • Manometers: Device to measure pressure differences, often with mercury levels.

  • Gauge Pressure: The difference between the atmospheric pressure and the gas pressure in containers.

9.6 The Buoyant Force

  • Archimedes’ Principle: A submerged object experiences an upward buoyant force equal to the weight of the fluid displaced.

  • Specific Gravity: Ratio of a substance's density to water's density at 4°C.

9.7 Fluid Flow

  • Types of Flow: Steady (constant velocity at points) and unsteady (changing velocity).

  • Viscous Forces: Opposes fluid flow; determined by the fluid's characteristics and movement speed.

9.8 Bernoulli’s Equation

  • Principle: For horizontal flow, higher speeds correspond to lower pressures (Bernoulli effect).

  • Equation Use: Applies to steady flow of ideal fluids along the same streamline.

9.9 Viscosity

  • Definition: A measure of a fluid's resistance to flow; affects how it behaves under force.

  • Temperature Effect: In liquids, viscosity decreases with increasing temperature; in gases, it increases.

9.10 Viscous Drag

  • Concept: The force acting against an object moving through a fluid; depends on speed and flow conditions.

  • Stokes's Law: Used to calculate viscous drag for spherical objects moving through fluids.

9.11 Surface Tension

  • Definition: The force per unit length at the surface of a liquid, caused by molecular cohesive forces.

  • Applications: Critical in biological systems, such as surfactants in lung function.