Fluid Mechanics Vocabulary Practice Cards

Vocabulary flashcards covering core definitions, fluid properties, pressure measurements, and hydrostatic structures from Fluid Mechanics Modules 1 and 2.

Fluid Mechanics

A branch of mechanics that deals with the actions of fluids in gas or liquid phase at rest or in motion.

Fluid

A substance that deforms continuously when acted on by a shearing stress of any magnitude.

Fluid Statics

The branch of fluid mechanics concerned with fluids at rest.

Fluid Dynamics

The branch of fluid mechanics concerned with fluids in motion.

Mass Density ($\rho$)

The mass of a fluid per unit volume, with standard density of water at $4\,^\circ\text{C}$ being $1000\,\text{kg/m}^3$.

Specific Weight ($\gamma$)

The gravitational force or weight per unit volume of a fluid, calculated as $\gamma = \rho g$.

Specific Volume ($v$)

The volume occupied per unit mass of a fluid, defined as $v = \frac{V}{m} = \frac{1}{\rho}$.

Specific Gravity (s.g.)

The ratio of the specific weight or density of a given fluid to the specific weight or density of water at the standard reference temperature of $4\,^\circ\text{C}$.

Dynamic Viscosity ($\mu_d$)

A measure of a fluid's resistance to deformation under shear stress, defined as $\mu_d = \frac{\tau}{dU/dy}$.

Kinematic Viscosity ($\mu_k$)

The ratio of the dynamic viscosity of a fluid to its mass density, calculated as $\mu_k = \frac{\mu_d}{\rho}$.

Surface Tension ($\sigma$)

A material property whereby a liquid at an interface exerts a force per unit length along the surface due to the cohesive nature of its molecules.

Cohesion

The attraction of molecules of the same kind.

Ideal Fluid

An imaginary fluid that is incompressible and has no viscosity.

Real Fluid

A fluid that possesses viscosity, which applies to all fluids in actual practice.

Newtonian Fluid

A real fluid in which the shear stress is directly proportional to the rate of shear strain or velocity gradient.

Non-Newtonian Fluid

A real fluid in which shear stress is not proportional to the rate of shear strain or velocity gradient.

Ideal Plastic Fluid

A fluid in which shear stress is greater than the yield value and shear stress is proportional to the rate of shear strain.

Coefficient of Compressibility

The fractional change in volume of a fluid per unit change in pressure in a constant temperature process.

Vapor Pressure

The equilibrium pressure exerted by free molecules escaping and condensing at a liquid surface at constant temperature.

Volatile Liquids

Liquids near their boiling point or that vaporize easily at normal temperatures, such as propane, butane, ammonia, and Freon.

Pressure ($P$)

The intensity of normal force acting per unit area, defined as $P = \frac{dF}{dA}$ or $P = \frac{F}{A}$.

Pascal (Pa)

The SI unit of pressure equivalent to $1\,\text{N/m}^2$.

Pascal's Law

A principle developed by Blaise Pascal stating that pressure on a fluid is equal in all directions and in all parts of the container.

Absolute Pressure

The true pressure measured relative to a perfect vacuum.

Gage Pressure

The pressure measured relative to the local atmospheric pressure level by most pressure recording instruments.

Atmospheric Pressure

The pressure obtained by barometric reading, equal to $101.325\,\text{kPa}$ or $760\,\text{mm\,Hg}$ at sea level.

Vacuum Pressure

The pressure measured below atmospheric pressure, equal to atmospheric pressure minus absolute pressure.

Mercury Barometer

An instrument that accurately measures atmospheric pressure by observing the height of a mercury column forced up a glass tube ($760\,\text{mm}$ at sea level).

Aneroid Barometer

An instrument measuring air pressure via the movement of a partially evacuated metal drum translated to a pointer using levers and springs.

Pressure Head ($h$)

The height $h$ of a column of homogeneous liquid of unit weight $\gamma$ that produces a pressure intensity $p$, given by $h = \frac{p}{\gamma}$.

Manometer

A tube (usually bent in a U-shape) containing a liquid of known specific gravity used to measure fluid pressure.

Open Type Manometer

A manometer with an atmospheric surface in one leg capable of measuring gage pressures.

Differential Type Manometer

A manometer without an atmospheric surface used strictly for measuring differences in pressure between two points.

Piezometer

The simplest open manometer, consisting of a tube tapped into a container wall where fluid rises to form a free surface.

Total Pressure

The force exerted by a static fluid normal to a plane or curved surface with which it comes in contact.

Center of Pressure

The specific point of application of the total resultant pressure force on a submerged surface.

Gravity Dam

A concrete or masonry dam structure that resists water pressure primarily through the sheer force of its massive weight.

Arch Dam

A concrete or masonry dam curved upstream into a reservoir that transfers water pressure forces to surrounding canyon walls.

Buttress Dam

A dam supported on the downstream side by several buttresses, allowing for a hollow or less massive structure.