# Physical and Chemical Symbols

The following is the meaning of the physics symbols and chemical symbols, along with their symbols and explanations:

#### In physics

Constant

α (lowercase alpha) denotes the fine structure constant (electromagnetic).
αG represents the fine structure constant of gravity.
ε0 denotes the vacuum permittivity or electric constant.
μ0 indicates vacuum magnetic permeability or magnetic constant.
σ (lowercase sigma) denotes the Stefan-Boltzmann constant.

#### In astronomy

The lowercase set of the Greek alphabet is used to denote the star in the Bayer naming system. For example, Alpha Centauri (α Cen), Gamma Cephei (γ Cep), Epsilon Eridani (ε Eri).

α (lowercase alpha) is also used to record the right-hand rise of a star, (δ is the declination, see below), which is the first equatorial coordinate.
γ (lower case gamma) is also used to denote a spring point (gamma point or “ point”); this point serves as a reference in the definition of coordinates, in the equatorial coordinate system.
δ (lowercase delta) is also used to note the declination of a star, see above).
Λ (uppercase lambda) denotes the cosmological constant, one of the parameters used to describe the evolution of the universe.
Ξ (uppercase ksi) indicates the compactness of a star, i.e. the ratio between its Schwarzschild radius (the radius that an object with the same mass would have if it were a black hole) and its actual size.
ϖ (a variant of the lower case pi) denotes the longitude of the periapsis, one of the orbital elements: ϖ = ω + Ω.
ω (lowercase omega) denotes the argument of periapsis, one of the orbital elements.
Ω (uppercase omega) designates the longitude of the ascending vertex, one of the orbital elements.

#### In chemistry

(lowercase gamma) indicates the activity coefficient in thermochemistry;
(capital delta) above the arrow in the reaction equation means the reaction was carried out by heating;
(lower case delta) denotes a chemical shift in nuclear magnetic resonance
(capital eta) shows the Eta function of Ludwig Boltzmann’s theorem H (theorem “Eta”), within the framework of the kinetic theory of gases;
(lowercase theta) indicates the temperature in degrees Celsius. Example: éb(cyclohexane) = 81°C. This symbol is mainly used to distinguish between relative temperature (in degrees Celsius) and absolute temperature (in kelvins, denoted by T): (°C) = T (K) – 273.15;
(capital kappa) denotes the Kappa index, which estimates the amount of chemical product required, during the bleaching of wood pulp, to obtain paper pulp that has a certain degree of whiteness;
(lowercase mu) indicates chemical potential in thermochemistry.
(lowercase nu) denotes the stoichiometric coefficient
(lowercase ksi) indicates the progress of a chemical reaction.
, , and are different types of covalent chemical bonds.

#### Electrochemistry

(lowercase lambda) represents the molar ionic conductivity of an ionic species such as K+.
(lowercase sigma) is used to denote the conductivity of some related ionic species such as K++Cl−. (This symbol is found for example in the formula S/l: Conductance G is equal to the conductivity multiplied by the surface of the electrolytic plate and divided by the distance between the plates; or in the formula = = Σ (λi Ci): conductivity equals the sum of the molar conductivity (see above) species multiplied by the molar concentration C).

#### In electromagnetism

(lowercase delta) indicates the length of the air gap of the magnetic material.
(lower case epsilon) denotes permittivity (specifically 0 denotes vacuum permittivity).
(lower case mu) indicates magnetic permeability (specifically 0 indicates vacuum magnetic permeability).
(lowercase sigma) indicates electrical conductivity.
(capital letter phi) denotes magnetic flux as well as electric flux.
(capital psi) is also used for electric flux, especially when it is necessary not to confuse the symbol with magnetic flux.

#### In electricity and electronics

(lowercase alpha) is used to record the temperature coefficient of an electronic or electrical component (resistor, capacitor, quartz, etc.)
(lowercase delta) is used to indicate the angle of loss (or delta tangent) of the dielectric or capacitor;
(lowercase rho) is used to express:
resistivity,
electric charge volume density;
(lowercase sigma) is used to indicate electrical conductivity;
(lower case phi) is used to record the phase shift (or phase at the origin) of an alternating current or sinusoidal signal;
(omega capital) is used to express the SI unit of electrical resistance, the ohm (Unicode \$2126).

#### In mechanics

(lowercase alpha) indicates angular acceleration;
(lower case epsilon) is used for relative elongation: = l/l ;
(lowercase eta) is often used in fluid mechanics to denote dynamic viscosity;
(lowercase symbol) is used for wavelengths;
(lowercase mu) is used:
in mechanics if fluid to show dynamic viscosity (as );
in dynamics to show the coefficient of friction (dynamic);
in statics 0 is also used to denote the coefficient of static friction;
(lowercase nu) is often used in fluid mechanics to denote kinematic viscosity;
(lowercase rho) or (lowercase mu) indicates density;
(lowercase sigma) is used
to determine angular momentum;
to determine normal tensile or compressive stresses;
(lowercase chi) is used to denote the coefficient of compressibility (thermodynamics and waves);
(omega capital) refers to the dynamics of the angular velocity of precession;
(lowercase omega) indicates the angular velocity.

#### In quantum mechanics

(capital psi) denotes the wave function (|Ψ(r)|² hence the probability density of presence).
(capital theta) indicates the angular part when described in spherical coordinates.

#### In optics and waves

(lowercase alpha) indicates angles: incident, reflection, refraction;
(lowercase letter) indicates the wavelength;
(lowercase nu) indicates the frequency, both waves and the natural frequency of an object (eg a string);
(lowercase ksi) denotes the wave function: = A sin(kx-ωt);
(lowercase sigma), indicates the wave number;
(lowercase omega) indicates the pulse (frequency multiplied by 2π).

#### Nuclear physics symbols

(lowercase alpha) is used to denote alpha particles, i.e. helium 4 nuclei;
(lowercase beta) is used in the index form + and , to denote positrons and electrons, respectively;
(lowercase gamma) is used to denote gamma radiation, and by extension photons in general;
(lower case epsilon) is often used to indicate electronic capture;
(lowercase sigma), indicates cross section

#### In thermodynamics

(lowercase alpha) indicates the coefficient of linear expansion;
(lowercase beta) denotes the coefficient equivalent to the thermodynamic temperature T (in kelvins) according to the formula , where is the Boltzmann constant;
(lowercase gamma) indicates the coefficient of volume expansion;
(lowercase theta) indicates the Celsius temperature (against T for absolute temperature);
(lowercase) indicates thermal conductivity.
(lowercase phi) is used to record the heat flux density;
(capital letter phi) indicates heat flux.

More common symbols

(small eta) is used to indicate the efficiency of energy transformation.
(lowercase nu) is used to indicate frequency.
(lowercase tau) indicates the time constant of a system.
(lowercase omega) is used to indicate the pulse: = 2 with frequency.
(capital delta) is used for the increment symbol ∆ (Unicode \$2206), which is why it is read as delta and is used to designate geometric lines, or intervals, or even variations. Example: t (delta t) indicates the duration, P (delta P) the pressure variation.

### Symbols for physical quantities and their international units

Space & Time
symbol quantity symbol SI unit
ss displacement, distance m meter
xyz cartesian coordinates m meter
cartesian unit vectors unitless
r̂, θ̂, φ̂ spherical unit vectors unitless
ρ̂, φ̂, ẑ cylindrical unit vectors unitless
normal unit vector unitless
tangential unit vector unitless
h height, depth m meter
ℓ, L length m meter
d distance, separation, thickness m meter
t thickness m meter
D diameter m meter
C circumference m meter
AA area, cross-sectional area, projected area, surface area m2 square meter
V volume m3 cubic meter
t time, duration s second
T period, periodic time s second
τ time constant s second
f frequency Hz hertz

#### Physics Symbols in Mechanics

Mechanics
symbol quantity symbol SI unit
vv velocity, speed m/s meter per second
aa acceleration m/s2 meter per second squared
acac centripetal acceleration, centrifugal acceleration m/s2 meter per second squared
gg gravitational field, acceleration due to gravity m/s2 meter per second squared
m mass kg kilogram
FF force N newton
FgWW force of gravity, weight N newton
FnNN normal force, normal N newton
Fffsfk force of friction (static, kinetic) N newton
μs, μk coefficient of friction (static, kinetic) unitless
pp momentum kg m/s kilogram meter per second
JJ impulse N s newton second
W work J joule
E energy, total energy J joule
KKtKr kinetic energy (translational, rotational) J joule
UUgUs potential energy (gravitational, spring) J joule
Vg gravitational potential J/kg joule per kilogram
η efficiency unitless
P power W watt
τ, τ torque N m newton meter
I moment of inertia kg m2 kilogram meter squared
LL angular momentum kg m2/s kilogram meter squared per second
HH angular impulse N m s newton meter second
k spring constant N/m newton per meter
P pressure Pa pascal
σ normal stress Pa pascal
τ shear stress Pa pascal
ρ density, volume mass density kg/m3 kilogram per cubic meter
σ area mass density, superficial mass density kg/m2 kilogram per square meter
λ linear mass density kg/m kilogram per meter
FBBB buoyancy, buoyant force N newton
qm mass flow rate kg/s kilogram per second
qV volume flow rate m3/s cubic meter per second
FDRR drag, aerodynamic drag, air resistance N newton
CCD drag coefficient, coefficient of drag unitless
η viscosity, dynamic viscosity Pa s pascal second
ν kinematic viscosity m2/s square meter per second
Ma mach number unitless
Re reynolds number unitless
Fr froude number unitless
E young’s modulus, modulus of elasticity Pa pascal
G shear modulus, modulus of rigidity Pa pascal
K bulk modulus, modulus of compression Pa pascal
ε linear strain unitless
γ shear strain unitless
θ volume strain unitless
γ surface tension N/m newton per meter

#### Thermal Physics

Thermal Physics
symbol quantity symbol SI unit
T temperature K kelvin
α linear expansivity, coefficient of linear thermal expansion K−1 inverse kelvin
β volume expansivity, coefficient of volume thermal expansion K−1 inverse kelvin
Q heat J joule
c specific heat, specific heat capacity J/kg K joule per kilogram kelvin
L latent heat, specific latent heat J/kg joule per kilogram
n amount of substance mole
N number of particles unitless
P heat flow rate W watt
k thermal conductivity W/m K watt per meter kelvin
ε emissivity unitless
U internal energy J joule
S entropy J/K joule per kelvin
w ways, number of identical microstates unitless
COP coefficient of performance unitless

#### Waves and Optics

Waves & Optics
symbol quantity symbol SI unit
λ wavelength m meter
vc wave speed m/s meter per second
I intensity W/m2 watt per square meter
L level dB, dNp decibel, decineper
n index of refraction, absolute index of refraction unitless
f focal length m meter
M magnification unitless

#### Electricity and Magnetism

Electricity & Magnetism
symbol quantity symbol SI unit
qQ charge, electric charge C coulomb
ρ charge density, volume charge density C/m3 coulomb per cubic meter
σ area charge density, superficial charge density C/m2 coulomb per square meter
λ linear charge density C/m coulomb per meter
FE, FE electric force, electrostatic force N newton
EE electric field N/C, V/m newton per coulomb, volt per meter
ΦE electric flux N m2/C, V m newton meter squared per coulomb, volt meter
UUE potential energy, electric potential energy J joule
V, VE voltage, potential, electric potential V volt
electromotive force, emf V volt
κ dielectric constant unitless
I current, electric current A ampère
Rr resistance, electrical resistance, internal resistance Ω ohm
ρ resistivity Ω m ohm meter
G conductance S siemens
σ conductivity S/m siemens per meter
FB, FB magnetic force N newton
BB magnetic field T tesla
ΦB magnetic flux Wb weber
N number of turns unitless
n turns per unit length, turns density m−1 inverse meter
η energy density J/m3 joule per cubic meter
SS poynting vector, intensity W/m2 watt per square meter

#### Modern Physics

Modern Physics
symbol quantity symbol SI unit
γ lorentz factor, lorentz gamma unitless
φ work function J joule
ψ(r,t), ψ(r)φ(t) wave function unitless
T½ half life s second
D dose, absorbed dose Gy gray
H effective dose Sv sievert

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