Mechanical Properties Of Fluids
Mechanical Properties of Fluids
Key Terms:

Density: Mass per unit volume. Remember this as the amount of matter packed into a given space

Specific gravity: Ratio of the density of a fluid to the density of water at 4°C. Think of it as how heavy a fluid is compared to water

Compressibility: Measure of the ability of a fluid to change volume under pressure. Imagine squeezing a balloon  the more compressible, the easier it is to squeeze.

Bulk modulus: Measure of the resistance of a fluid to uniform compression. Think of it as the fluid’s stiffness  the higher the bulk modulus, the harder it is to compress.

Viscosity: Measure of the resistance of a fluid to flow. Remember this as the “thickness” or “gooeyness” of a fluid

Newtonian fluid: A fluid whose viscosity is constant. Think of water or honey  their viscosity doesn’t change much with the rate of flow

NonNewtonian fluid: A fluid whose viscosity varies with the rate of shear stress. Imagine ketchup or toothpaste  they are thicker when you apply a slow force, but thinner when you apply a quick force.

Laminar flow: Fluid flow in which layers of fluid move smoothly past each other without mixing. Think of water flowing through a pipe  the layers of water move smoothly without mixing.

Turbulent flow: Fluid flow in which layers of fluid mix together. Imagine water flowing through a rapids  the layers of water mix and create turbulence

Bernoulli’s equation: Equation relating the pressure, velocity, and height of a fluid in steady flow. Remember this as the “energy equation” for fluids

Pascal’s law: Pressure applied to a confined fluid is transmitted equally to every point in the fluid. Picture a hydraulic system  the pressure applied to one part of the fluid is transmitted to all other parts

Archimedes’ principle: Buoyant force acting on an object submerged in a fluid is equal to the weight of the fluid displaced by the object. Think of a boat floating on water  the buoyant force keeps it afloat.

Capillarity: Rise or fall of a liquid in a narrow tube due to surface tension. Visualize a straw in a glass of water  the water rises inside the straw due to capillarity.

Surface tension: Force acting at the surface of a liquid that tends to contract the surface and minimize its area. Imagine a water droplet  it takes the shape of a sphere to minimize surface tension

Cohesion: Force of attraction between molecules of the same substance. Think of water droplets holding together due to cohesion

Adhesion: Force of attraction between molecules of different substances. Visualize water sticking to glass due to adhesion

Wetting: Spreading of a liquid on a surface due to adhesion. Imagine water spreading on a clean glass surface due to wetting.

Nonwetting: Nonspreading of a liquid on a surface due to cohesion. Think of water beading up on a waxed car surface due to nonwetting.