Properties of Fluids Quiz

Study Notes

Distinction between Fluids and Solids

Fluids can flow and do not maintain a fixed shape, adapting to the boundaries of their containers.
Solids have a definite shape and do not deform easily under external forces.

Density, Specific Weight, and Specific Gravity

Density: Mass per unit volume of a substance, commonly expressed in kg/m³.
Specific Weight: Weight per unit volume, calculated as γ = ρg, where ρ is density and g is acceleration due to gravity.
Specific Gravity: Ratio of the density of a substance to the density of a reference (usually water at 4°C), dimensionless.

Viscosity

Kinematic Viscosity: Measure of a fluid's internal resistance to flow, defined as the ratio of dynamic viscosity to density, expressed in m²/s.
Dynamic Viscosity: Measure of a fluid's resistance to flow under an applied force, expressed in pascal-seconds (Pa·s).
Viscosity decreases with increasing temperature for liquids; for gases, viscosity typically increases with temperature.
Newton's Law of Viscosity: States that the shear stress between fluid layers is proportional to the rate of shear strain, expressed as τ = μ(du/dy), where τ is shear stress, μ is dynamic viscosity, and du/dy is the velocity gradient.

Vapor Pressure and Boiling Point

Vapor Pressure: The pressure exerted by a vapor in equilibrium with its liquid or solid phase; increases with temperature.
Boiling Point: The temperature at which a liquid's vapor pressure equals the external pressure, causing it to change to vapor.

Cavitation

Occurs when local pressure drops below vapor pressure, resulting in the formation of vapor bubbles; can cause damage in hydraulic machinery.

Surface Tension

The cohesive force at the surface of a liquid that causes it to minimize surface area, measured in N/m.
Influences phenomena like droplet formation and liquid spreading.

Capillarity

The ability of a liquid to flow in narrow spaces without external forces, driven by surface tension and adhesive forces between liquid and solid surfaces, common in liquids like water in tubes or porous materials.

Distinction between Fluids and Solids

Fluids can flow and take the shape of their container, while solids maintain a fixed shape.
The ability to deform continuously under applied stress is a characteristic of fluids, unlike solids which resist deformation.

Density, Specific Weight, and Specific Gravity

Density: Mass per unit volume of a substance, typically measured in kg/m³.
Specific Weight: Weight per unit volume, calculated as the product of density and gravitational acceleration (γ = ρ * g).
Specific Gravity: Ratio of the density of a substance to the density of a reference substance (usually water), dimensionless.

Viscosity

Kinematic viscosity: Ratio of dynamic viscosity to density (ν = μ / ρ), measuring how a fluid flows under gravity.
Dynamic viscosity: Measure of a fluid's resistance to shear or flow (μ), with units of Pa·s.
Viscosity generally decreases with increasing temperature for most liquids, enhancing flow.
Newton's Law of Viscosity: States that the shear stress is proportional to the shear rate, expressed as τ = μ(du/dy).

Vapor Pressure and Boiling Point

Vapor Pressure: Pressure exerted by vapor in equilibrium with its liquid phase at a given temperature, indicates volatility.
Boiling Point: The temperature at which a substance's vapor pressure equals the atmospheric pressure, causing a transition from liquid to gas.

Cavitation

Occurs when local pressure falls below vapor pressure in a fluid, leading to the formation of vapor-filled cavities or bubbles.
Can cause damage in pumps and turbines due to shock waves generated when the bubbles collapse.

Surface Tension and Capillarity

Surface Tension: The energy required to increase the surface area of a liquid, creating a "skin" effect at the surface due to cohesive forces between molecules.
Capillarity: The ability of a liquid to flow in narrow spaces without the assistance of external forces, influenced by surface tension and adhesive forces with surrounding surfaces.

Description

Test your understanding of the basic concepts and definitions related to fluids. This quiz covers the distinctions between fluids and solids, various fluid properties like density, viscosity, and surface tension, as well as the effects of temperature and other factors. Prepare to explore key fluid mechanics topics!