Chapter 6 – Physical Principles of Respiratory Care

Vocabulary flashcards summarizing essential terms and definitions from Chapter 6: Physical Principles of Respiratory Care.

Solid

State of matter with fixed volume and shape; molecules have strong mutual attraction and only vibrate in place (“jiggle”).

Liquid

State of matter with fixed volume but variable shape; molecules have moderate mutual attraction and slide past one another.

Gas

State of matter with no fixed volume or shape; molecules move rapidly in random motion with weak attractive forces.

Plasma

Ionized gas containing neutral atoms, free electrons, and nuclei; responds to electromagnetic forces.

Internal Energy

Total potential and kinetic energy contained in the molecules of a substance.

Potential Energy

Energy of position due to attractive forces between molecules; dominant in solids and liquids.

Kinetic Energy

Energy of motion; dominant contributor to the internal energy of gases.

First Law of Thermodynamics

Energy can neither be created nor destroyed; heat moves from hotter to cooler objects until equilibrium.

Conduction

Heat transfer through direct molecular contact, chiefly in solids.

Convection

Heat transfer via mixing of fluid molecules at different temperatures, occurring in liquids and gases.

Radiation

Heat transfer without direct contact, via electromagnetic waves.

Evaporation

Vaporization process where a liquid absorbs heat from surroundings and becomes gas, causing cooling.

Condensation

Change of state from gas to liquid; releases latent heat to surroundings.

Vaporization

General term for conversion from liquid to gas (includes boiling and evaporation).

Temperature

Measure of average kinetic energy of molecular motion.

Absolute Zero

Theoretical temperature (0 K or –273 °C) at which molecular kinetic energy is zero.

Kelvin Scale

Thermodynamic temperature scale starting at absolute zero; K = °C + 273.

Fahrenheit Scale

Temperature scale where water freezes at 32 °F and boils at 212 °F.

Celsius Scale

Temperature scale where water freezes at 0 °C and boils at 100 °C.

Melting Point

Temperature at which a solid becomes a liquid.

Freezing Point

Temperature at which a liquid becomes a solid (same as its melting point).

Sublimation

Direct change from solid to vapor without passing through liquid state (e.g., dry ice).

Pressure (Liquid)

Force exerted by a liquid per unit area, dependent on liquid height and density.

Buoyancy

Upward force exerted by a fluid, because pressure beneath an object exceeds pressure above it.

Specific Gravity

Ratio of the density of a substance to the density of a reference substance (usually water).

Viscosity

Internal resistance to flow due to cohesive forces; higher viscosity means thicker fluid.

Cohesion

Attractive force between like molecules in a liquid.

Adhesion

Attractive force between unlike molecules, such as liquid and container wall.

Surface Tension

Force created by cohesive molecules at a liquid surface; causes droplets to form spheres.

Capillary Action

Upward movement of liquid in a narrow tube due to combined adhesive forces and surface tension.

Boiling Point

Temperature at which a liquid’s vapor pressure equals atmospheric pressure, allowing bulk vaporization.

Absolute Humidity

Actual mass of water vapor in a given volume of gas, expressed in mg/L.

Relative Humidity (RH)

Percentage ratio of actual water vapor content to the maximum capacity at a given temperature.

Dew Point

Temperature at which water vapor in a gas begins to condense at a given pressure.

Molar Volume

Volume occupied by one mole of an ideal gas at STP (22.4 L).

Gas Density

Mass per unit volume of a gas.

Gaseous Diffusion

Movement of gas molecules from areas of high concentration to low concentration.

Partial Pressure

Pressure exerted by a single gas in a mixture proportional to its concentration.

Dalton’s Law

Total pressure of a gas mixture equals the sum of the partial pressures of each component gas.

Henry’s Law

Amount of gas dissolved in a liquid is directly proportional to its partial pressure, at constant temperature.

Boyle’s Law

For a constant temperature, gas volume varies inversely with pressure (P₁V₁ = P₂V₂).

Charles’s Law

For constant pressure, gas volume varies directly with absolute temperature (V ∝ T).

Gay-Lussac’s Law

For constant volume, gas pressure varies directly with absolute temperature (P ∝ T).

Combined Gas Law

Relationship combining Boyle’s, Charles’s, and Gay-Lussac’s laws (P₁V₁/T₁ = P₂V₂/T₂).

Critical Temperature

Highest temperature at which a substance can exist as a liquid, regardless of pressure.

Critical Pressure

Pressure required to maintain a substance as liquid at its critical temperature.

Laminar Flow

Smooth fluid motion in parallel layers; pressure–flow described by Poiseuille’s law.

Poiseuille’s Law

For laminar flow in a tube, ΔP = 8ηLQ/πr⁴, predicting pressure needed for a given flow.

Turbulent Flow

Chaotic fluid movement with eddy currents; onset predicted by Reynolds number.

Reynolds Number

Dimensionless value (Re = ρvD/μ) indicating flow pattern; Re > 2000 usually signals turbulence.

Transitional Flow

Mixed pattern containing both laminar and turbulent characteristics.

Bernoulli Principle

Increase in fluid velocity causes a corresponding decrease in static pressure and potential energy.

Venturi Effect

Pressure drop and velocity increase that occur when fluid passes through a constricted section of a tube.

Fluid Entrainment

Use of a low-pressure region (created by Venturi) to draw a second fluid into a primary flow stream.

Fluidics

Engineering field applying fluid dynamic principles to control circuits without moving parts.

Coanda Effect

Tendency of a fluid jet to attach to a nearby surface and follow its contour.