Mechanics
a
Acceleration
Rate of change of velocity with respect to time.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
a = dv/dt
a is acceleration, v is velocity, and t is time. The derivative dv/dt means acceleration is how quickly velocity changes.
Fluids
Adhesion
Attraction between unlike materials, such as a liquid and a solid surface.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Thermodynamics
Q = 0
Adiabatic Process
Thermodynamic process with no heat transfer across the system boundary.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Formula
Q = 0
Q is heat transfer. In an adiabatic process, Q is zero because no heat crosses the system boundary.
Fluids
Airfoil
Streamlined shape designed to produce lift when air flows over it.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Mechanics
A
Amplitude
Maximum displacement of an oscillating system from its equilibrium position.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Structures
Faxial
Axial Load
Load applied along the longitudinal axis of a member, causing tension or compression.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
Structures
M
Bending Moment
Internal moment that causes a beam or structural member to bend.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
Formula
M = Fd
M is bending moment, F is force, and d is the perpendicular distance from the point or section being considered.
Fluids
Bernoulli's Principle
Energy relationship for steady, incompressible, inviscid flow along a streamline.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
P + 1/2 ρv² + ρgz = constant
P is static pressure, ρ is density, v is velocity, g is gravitational acceleration, and z is elevation.
Thermodynamics
Boiling Point
Temperature at which a liquid vapor pressure equals the surrounding pressure.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Physics
k
Boltzmann Constant
Physical constant relating average particle energy to absolute temperature.
In applied physics this term connects engineering models to fundamental constants or microscopic behavior.
Formula
k = 1.380649 × 10⁻²³ J/K
k is the Boltzmann constant. It converts absolute temperature in kelvin into an energy scale per particle.
Materials
K
Bulk Modulus
Measure of resistance to uniform compression.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
K = -V(dP/dV)
K is bulk modulus, V is volume, P is pressure, and dP/dV describes how pressure changes as volume changes.
Electrical
C
Capacitance
Ability of a component or system to store electric charge per unit voltage.
In electrical engineering this term is used to describe circuit behavior, stored energy, voltage, current, or material electrical response.
Formula
C = Q/V
C is capacitance, Q is stored charge, and V is voltage.
Fluids
Capillary Action
Movement of liquid through narrow spaces caused by adhesion, cohesion, and surface tension.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Mechanics
Fc
Centripetal Force
Force directed toward the center of a circular path.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
F_c = mv²/r
F_c is centripetal force, m is mass, v is tangential speed, and r is path radius.
Mechanics
μ
Coefficient of Friction
Ratio of friction force to normal force between two contacting surfaces.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
μ = F_f/N
μ is coefficient of friction, F_f is friction force, and N is the normal force pressing the surfaces together.
Materials
σc
Compressive Stress
Stress caused by forces that tend to shorten or compress a material.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
σ = F/A
σ is normal stress, F is applied force, and A is the loaded cross-sectional area.
Heat Transfer
Conduction
Heat transfer through a material due to molecular interaction without bulk motion.
In heat transfer work this term helps estimate conduction, convection, radiation, or the thermal response of a material or fluid.
Formula
q = -kA(dT/dx)
q is heat transfer rate, k is thermal conductivity, A is area, and dT/dx is the temperature gradient.
Fluids
Control Volume
Defined region in space used to analyze mass, momentum, and energy flow.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Heat Transfer
Convection
Heat transfer between a surface and a moving fluid.
In heat transfer work this term helps estimate conduction, convection, radiation, or the thermal response of a material or fluid.
Formula
q = hAΔT
q is convective heat transfer rate, h is convection coefficient, A is area, and ΔT is temperature difference.
Materials
Creep
Time-dependent permanent deformation under sustained load or stress.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Fluids
ρ
Density
Mass per unit volume of a substance.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
ρ = m/V
ρ is density, m is mass, and V is volume.
Electrical
Diode
Semiconductor device that ideally allows current to flow in one direction.
In electrical engineering this term is used to describe circuit behavior, stored energy, voltage, current, or material electrical response.
Mechanics
s
Displacement
Vector change in position from an initial point to a final point.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Fluids
Fd
Drag Force
Resistance force on an object moving through a fluid.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
F_d = 1/2 ρv²C_dA
F_d is drag force, ρ is fluid density, v is speed, C_d is drag coefficient, and A is reference area.
Fluids
μ
Dynamic Viscosity
Measure of a fluid resistance to shear deformation or flow.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
τ = μ(du/dy)
τ is shear stress, μ is dynamic viscosity, and du/dy is the velocity gradient normal to the flow direction.
Materials
Elastic Limit
Maximum stress a material can withstand and still return to its original shape.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Materials
E
Elastic Modulus
Measure of material stiffness in the elastic region.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
E = σ/ε
E is elastic modulus, σ is stress, and ε is strain in the linear elastic range.
Electrical
ρe
Electrical Resistivity
Material property describing resistance to electric current flow.
In electrical engineering this term is used to describe circuit behavior, stored energy, voltage, current, or material electrical response.
Formula
ρ_e = RA/L
ρ_e is electrical resistivity, R is resistance, A is conductor area, and L is conductor length.
Electrical
EMF
Electromotive Force
Voltage generated by a source when no current is flowing.
In electrical engineering this term is used to describe circuit behavior, stored energy, voltage, current, or material electrical response.
Thermodynamics
S
Entropy
Thermodynamic property associated with energy dispersal and irreversibility.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Formula
dS = δQ_rev/T
dS is entropy change, δQ_rev is reversible heat transfer, and T is absolute temperature.
Mechanics
Equilibrium
Condition where resultant forces, moments, or driving potentials are balanced.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
ΣF = 0, ΣM = 0
ΣF is the sum of forces and ΣM is the sum of moments. Both must be zero for static equilibrium.
Structures
Pcr
Euler Buckling
Elastic instability load for a slender column under compression.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
Formula
P_cr = π²EI/(KL)²
P_cr is critical buckling load, E is elastic modulus, I is second moment of area, K is effective length factor, and L is column length.
Materials
Fatigue
Progressive damage caused by repeated or fluctuating stress cycles.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Fluids
Q
Flow Rate
Volume of fluid passing through a section per unit time.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
Q = Av
Q is volumetric flow rate, A is flow area, and v is average velocity.
Mechanics
F
Force
Interaction that changes or tends to change motion.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
F = ma
F is force, m is mass, and a is acceleration.
Structures
FBD
Free Body Diagram
Diagram showing all external forces and moments acting on an isolated body.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
Mechanics
f
Frequency
Number of cycles or oscillations per unit time.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
f = 1/T
f is frequency and T is period, the time for one cycle.
Fluids
Pg
Gauge Pressure
Pressure measured relative to local atmospheric pressure.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
P_g = P_abs - P_atm
P_g is gauge pressure, P_abs is absolute pressure, and P_atm is atmospheric pressure.
Mechanical Design
Gear Ratio
Ratio between rotational speeds or tooth counts in a gear pair.
In mechanical design this term is used when sizing machine elements, checking motion, or comparing power transmission behavior.
Formula
GR = N_driven/N_driver
GR is gear ratio, N_driven is driven gear teeth or speed reference, and N_driver is driver gear teeth or speed reference.
Mechanics
g
Gravitational Acceleration
Acceleration due to gravity near a massive body.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
g = 9.80665 m/s²
g is standard gravitational acceleration near Earth surface and is commonly used for weight, head, and projectile calculations.
Thermodynamics
C
Heat Capacity
Heat required to raise the temperature of a body by one kelvin.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Formula
C = Q/ΔT
C is heat capacity, Q is heat added or removed, and ΔT is temperature change.
Heat Transfer
Heat Transfer
Movement of thermal energy due to temperature difference.
In heat transfer work this term helps estimate conduction, convection, radiation, or the thermal response of a material or fluid.
Materials
Hooke's Law
Linear elastic relation between force and displacement, or stress and strain.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
F = kx
F is restoring force, k is stiffness, and x is displacement from equilibrium.
Fluids
Dh
Hydraulic Diameter
Equivalent diameter used for non-circular ducts and channels.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
D_h = 4A/P_w
D_h is hydraulic diameter, A is flow area, and P_w is wetted perimeter.
Mechanics
J
Impulse
Product of force and time, equal to change in momentum.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
J = FΔt
J is impulse, F is force, and Δt is the time interval over which the force acts.
Electrical
L
Inductance
Circuit property that opposes change in current through stored magnetic energy.
In electrical engineering this term is used to describe circuit behavior, stored energy, voltage, current, or material electrical response.
Formula
V = L(di/dt)
V is induced voltage, L is inductance, and di/dt is the rate of change of current.
Thermodynamics
U
Internal Energy
Microscopic energy stored in a system due to molecular motion and interactions.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Thermodynamics
Isentropic Process
Ideal thermodynamic process with constant entropy.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Formula
s = constant
s is specific entropy. In an ideal isentropic process it remains unchanged from inlet to outlet or state to state.
Thermodynamics
Isothermal Process
Thermodynamic process occurring at constant temperature.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Formula
T = constant
T is absolute temperature. In an isothermal process the temperature is held constant while other properties may change.
Units
J
Joule
SI unit of energy, work, and heat.
As a unit term, it is used to keep engineering calculations dimensionally consistent and to convert results between systems.
Formula
1 J = 1 N·m
J is joule, N is newton, and m is metre. One joule is the work done by one newton acting through one metre.
Units
K
Kelvin
SI base unit of thermodynamic temperature.
As a unit term, it is used to keep engineering calculations dimensionally consistent and to convert results between systems.
Formula
K = °C + 273.15
K is kelvin and °C is degrees Celsius. The offset 273.15 converts Celsius temperature to absolute temperature.
Fluids
ν
Kinematic Viscosity
Dynamic viscosity divided by density.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
ν = μ/ρ
ν is kinematic viscosity, μ is dynamic viscosity, and ρ is density.
Fluids
Laminar Flow
Smooth, orderly fluid motion with little mixing between layers.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
Re < about 2300 in pipes
Re is Reynolds number. In circular pipe flow, values below about 2300 are usually treated as laminar.
Structures
Load Factor
Multiplier or ratio comparing applied load to a reference or design load.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
Fluids
Ma
Mach Number
Ratio of flow velocity to local speed of sound.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
Ma = v/a
Ma is Mach number, v is flow speed, and a is local speed of sound.
Structures
I
Moment of Inertia
Geometric property describing resistance to bending about an axis.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
Formula
I = ∫y² dA
I is second moment of area, y is distance from the neutral axis, and dA is an area element.
Mechanics
fn
Natural Frequency
Frequency at which a system tends to vibrate after disturbance.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
f_n = 1/(2π)√(k/m)
f_n is natural frequency, k is stiffness, and m is vibrating mass.
Units
N
Newton
SI unit of force.
As a unit term, it is used to keep engineering calculations dimensionally consistent and to convert results between systems.
Formula
1 N = 1 kg·m/s²
N is newton, kg is kilogram, m is metre, and s is second. The unit follows directly from F = ma.
Units
Ω
Ohm
SI unit of electrical resistance.
As a unit term, it is used to keep engineering calculations dimensionally consistent and to convert results between systems.
Formula
1 Ω = 1 V/A
Ω is ohm, V is volt, and A is ampere. One ohm gives one ampere of current for one volt of potential difference.
Units
Pa
Pascal
SI unit of pressure and stress.
As a unit term, it is used to keep engineering calculations dimensionally consistent and to convert results between systems.
Formula
1 Pa = 1 N/m²
Pa is pascal, N is newton, and m² is square metre. It represents one newton of force spread over one square metre.
Materials
Plastic Deformation
Permanent deformation that remains after load is removed.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Materials
ν
Poisson's Ratio
Negative ratio of transverse strain to axial strain.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
ν = -ε_trans/ε_axial
ν is Poisson ratio, ε_trans is transverse strain, and ε_axial is axial strain.
Mechanics
P
Power
Rate of doing work or transferring energy.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
P = W/t
P is power, W is work or energy transferred, and t is time.
Fluids
P
Pressure
Normal force per unit area.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
P = F/A
P is pressure, F is normal force, and A is area.
Heat Transfer
Radiation
Heat transfer by electromagnetic waves without requiring a material medium.
In heat transfer work this term helps estimate conduction, convection, radiation, or the thermal response of a material or fluid.
Formula
q = εσA(T_s⁴ - T_sur⁴)
q is radiative heat transfer rate, ε is emissivity, σ is the Stefan-Boltzmann constant, A is area, and T is absolute temperature.
Materials
Resilience
Ability of a material to absorb energy elastically and recover.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Electrical
R
Resistance
Opposition to electric current flow.
In electrical engineering this term is used to describe circuit behavior, stored energy, voltage, current, or material electrical response.
Formula
R = V/I
R is resistance, V is voltage, and I is current.
Fluids
Re
Reynolds Number
Dimensionless ratio of inertial forces to viscous forces in a fluid.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
Re = ρvD/μ
Re is Reynolds number, ρ is density, v is velocity, D is characteristic length, and μ is dynamic viscosity.
Materials
G
Shear Modulus
Measure of stiffness in shear deformation.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
G = τ/γ
G is shear modulus, τ is shear stress, and γ is shear strain.
Materials
τ
Shear Stress
Stress component acting parallel to a surface.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
τ = F/A
τ is shear stress, F is shear force, and A is the shear area.
Thermodynamics
c
Specific Heat
Heat required to raise unit mass by one kelvin.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Formula
Q = mcΔT
Q is heat energy, m is mass, c is specific heat, and ΔT is temperature change.
Materials
ε
Strain
Deformation per unit original length.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
ε = ΔL/L
ε is strain, ΔL is change in length, and L is original length.
Materials
σ
Stress
Internal force per unit area within a material.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
σ = F/A
σ is normal stress, F is applied force, and A is the loaded cross-sectional area.
Fluids
γ
Surface Tension
Energy required to increase liquid surface area, often expressed as force per unit length.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Heat Transfer
k
Thermal Conductivity
Material property describing ability to conduct heat.
In heat transfer work this term helps estimate conduction, convection, radiation, or the thermal response of a material or fluid.
Formula
q = -kA(dT/dx)
q is heat transfer rate, k is thermal conductivity, A is area, and dT/dx is the temperature gradient.
Thermodynamics
Thermodynamic System
Quantity of matter or region in space selected for energy analysis.
In thermodynamics this term describes energy, temperature, state, or process behavior for closed systems, control volumes, and power or refrigeration cycles.
Mechanics
τ
Torque
Moment of a force that tends to produce rotation.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
τ = rF
τ is torque, r is moment arm, and F is applied force.
Fluids
Turbulent Flow
Irregular fluid motion with strong mixing and velocity fluctuations.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
Re > about 4000 in pipes
Re is Reynolds number. In circular pipe flow, values above about 4000 are usually treated as turbulent.
Materials
Ultimate Strength
Maximum engineering stress a material can withstand before failure.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Math
Unit Vector
Vector with magnitude one used to specify direction.
In engineering mathematics this term supports vector, geometry, and modeling operations used across disciplines.
Mechanics
v
Velocity
Rate of change of displacement with respect to time.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
v = ds/dt
v is velocity, s is displacement, and t is time.
Fluids
Viscosity
General measure of a fluid resistance to flow or shear.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Fluids
Q
Volumetric Flow Rate
Volume passing through a cross-section per unit time.
In fluid mechanics this term is used to model pressure, flow, resistance, or fluid forces in pipes, ducts, channels, pumps, and external flow.
Formula
Q = Av
Q is volumetric flow rate, A is flow area, and v is average velocity.
Mechanics
W
Work
Energy transferred when a force acts through a distance.
In engineering calculations this term is used to describe motion, loads, energy transfer, or dynamic response. It usually appears with a defined sign convention and unit system.
Formula
W = Fd
W is work, F is force, and d is displacement in the force direction.
Materials
σy
Yield Strength
Stress at which a material begins to deform plastically.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Materials
E
Young's Modulus
Elastic modulus for tensile or compressive loading.
In materials engineering this term helps connect load, deformation, stiffness, or failure behavior to a measurable material property.
Formula
E = σ/ε
E is elastic modulus, σ is stress, and ε is strain in the linear elastic range.
Structures
Zero Deflection
Condition where displacement at a selected point is zero.
In structural analysis this term helps describe how members carry load, deform, or remain stable. It is commonly used when checking beams, columns, frames, and connections.
