Definitions Glossary

Term	Definition	Unit / Dimensions
Stress (σ)	Restoring force per unit cross-sectional area of material	Pa = N/ $m^{2}$ , [ $M^{1}$ $L^{-1}$ $T^{-2}$ ]
Strain	Fractional deformation (dimensionless ratio of change to original)	Dimensionless
Hooke's Law	Within elastic limit, stress is directly proportional to strain	—
Young's Modulus (Y)	Ratio of longitudinal stress to longitudinal strain for a wire	Pa, [ $M^{1}$ $L^{-1}$ $T^{-2}$ ]
Bulk Modulus (B)	Ratio of normal stress to volumetric strain; B = −V(dP/dV)	Pa, [ $M^{1}$ $L^{-1}$ $T^{-2}$ ]
Shear Modulus (G)	Ratio of shear stress to shear strain	Pa, [ $M^{1}$ $L^{-1}$ $T^{-2}$ ]
Compressibility	Reciprocal of Bulk modulus (1/B); ease of volume compression	$Pa^{-1}$
Elastic limit	Maximum stress beyond which material does not return to original shape	Pa
Yield point	Stress at which large plastic deformation begins with little extra stress	Pa
Pascal's Law	Pressure applied to enclosed fluid is transmitted equally in all directions	—
Bernoulli's Equation	Energy conservation for ideal fluid flow: P + ½ρ $v^{2}$ + ρgh = constant	Pa
Viscosity (η)	Measure of internal fluid friction; Newton's law: F = ηA(dv/dx)	Pa·s, [ $M^{1}$ $L^{-1}$ $T^{-1}$ ]
Terminal Velocity (v_t)	Constant velocity reached when gravity = drag + buoyancy	m/s, [ $M^{0}$ $L^{1}$ $T^{-1}$ ]
Surface Tension (S)	Force per unit length acting along fluid surface; S = F/L	N/m, [ $M^{1}$ $L^{0}$ $T^{-2}$ ]
Excess Pressure	Pressure difference across a curved liquid surface; 2S/R (drop), 4S/R (bubble)	Pa
Capillary Rise	Rise (or fall) of liquid in a narrow tube; h = 2S cosθ/(ρgr)	m
Contact Angle (θ)	Angle between liquid surface and solid at their junction	degrees (°)
Thermal Conductivity (K)	Rate of heat flow per unit area per unit temperature gradient	W $m^{-1}$ $K^{-1}$
Stefan-Boltzmann Constant (σ)	Constant in radiation law: σ = $5.67 \times 10^{-8}$ W $m^{-2}$ $K^{-4}$	W $m^{-2}$ $K^{-4}$
Equation of Continuity	$A_{1}$ v_{1} = $A_{2}$ v_{2} for incompressible fluid (mass conservation)	—