Reference
space & time, mechanics, thermal physics, waves & optics, electricity & magnetism, modern physics, mathematics, greek alphabet, astronomy, music
Style sheet
These are the conventions used in this book.
- Vector quantities (F, g, v) are written in a bold, serif font — including vector quantities written with Greek symbols (α, τ, ω).
- Scalar quantities (m, K, t) and the magnitudes of vector quantities (F, g, v) are written in an italic, serif font — except for Greek symbols (α, τ, ω), which use a roman serif font.
- Mathematical symbols use a roman, serif font (½, +, √, cos) — except when they are applied to calculations with units.
- Units are written with a roman, sans-serif font (m, N, ℃) as are mathematical operations with numbers and units (7 kg × 10 m/s ÷ 3 s = 23.3 N).
Symbols for physical quantities and their international units
Space & Time symbol | quantity | symbol | SI unit |
r, r | position, separation, radius, radius of curvature | m | meter |
s, s | displacement, distance | m | meter |
θ, φ, θ, φ | angle, angular displacement, angular separation, rotation angle | rad | radian |
x, y, z | cartesian coordinates | m | meter |
î, ĵ, k̂ | cartesian unit vectors | unitless |
r, θ, φ | spherical coordinates | m, rad | meter, radian |
r̂, θ̂, φ̂ | spherical unit vectors | unitless |
ρ, φ, z | cylindrical coordinates | m, rad | meter, radian |
ρ̂, φ̂, ẑ | cylindrical unit vectors | unitless |
n̂ | normal unit vector | unitless |
t̂ | 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 |
A, A | 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 |
ω | angular frequency | rad/s | radian per second |
Mechanics symbol | quantity | symbol | SI unit |
v, v | velocity, speed | m/s | meter per second |
a, a | acceleration | m/s2 | meter per second squared |
ac, ac | centripetal acceleration, centrifugal acceleration | m/s2 | meter per second squared |
g, g | gravitational field, acceleration due to gravity | m/s2 | meter per second squared |
m | mass | kg | kilogram |
F, F | force | N | newton |
Fg, W, W | force of gravity, weight | N | newton |
Fn, N, N | normal force, normal | N | newton |
Ff, fs, fk | force of friction (static, kinetic) | N | newton |
μs, μk | coefficient of friction (static, kinetic) | unitless |
p, p | momentum | kg m/s | kilogram meter per second |
J, J | impulse | N s | newton second |
W | work | J | joule |
E | energy, total energy | J | joule |
K, Kt, Kr | kinetic energy (translational, rotational) | J | joule |
U, Ug, Us | potential energy (gravitational, spring) | J | joule |
Vg | gravitational potential | J/kg | joule per kilogram |
η | efficiency | unitless |
P | power | W | watt |
ω, ω | rotational velocity, rotational speed | rad/s | radian per second |
α, α | rotational acceleration | rad/s2 | radian per second squared |
τ, τ | torque | N m | newton meter |
I | moment of inertia | kg m2 | kilogram meter squared |
L, L | angular momentum | kg m2/s | kilogram meter squared per second |
H, H | 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 |
FB, B, B | buoyancy, buoyant force | N | newton |
qm | mass flow rate | kg/s | kilogram per second |
qV | volume flow rate | m3/s | cubic meter per second |
FD, R, R | drag, aerodynamic drag, air resistance | N | newton |
C, CD | 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 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 & Optics symbol | quantity | symbol | SI unit |
λ | wavelength | m | meter |
v, c | 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 & Magnetism symbol | quantity | symbol | SI unit |
q, Q | 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 |
E, E | 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 |
U, UE | potential energy, electric potential energy | J | joule |
V, VE | voltage, potential, electric potential | V | volt |
ℰ | electromotive force, emf | V | volt |
C | capacitance | F | farad |
κ | dielectric constant | unitless |
I | current, electric current | A | ampère |
R, r | 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 |
B, B | 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 |
S, S | poynting vector, intensity | W/m2 | watt per square meter |
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 | equivalent dose | Sv | sievert |
E | effective dose | Sv | sievert |
wR | radiation weighting factor | unitless |
wT | tissue weighting factor | unitless |
Miscellaneous symbols
Mathematical symbols and notation symbol | description |
+ | plus, add, sum, positive |
− | minus, subtract, difference, negative |
± | uncertainty, error, plus-minus |
· | multiply, dot, dot product, scalar product |
× | multiply, cross, cross product, vector product |
÷, / | divide |
x2 | square |
x3 | cube |
√ | square root, root, radical |
∛ | cube root |
1x, x−1 | invert, reciprocal |
= | equal to, equality |
≈ | approximately equal to |
∝ | proportional to |
≠ | not equal to, inequality |
~ | on the order of |
< | less than |
> | greater than |
≤ | less than or equal to |
≥ | greater than or equal to |
≪ | much less than |
≫ | much greater than |
⇒, ⇐ | logical implication |
⇔ | logical equivalence |
→ | approaches |
… | and so on |
∴ | therefore |
f(x) | function |
sin | sine |
cos | cosine |
tan | tangent |
sinh | hyperbolic sine |
cosh | hyperbolic cosine |
tanh | hyperbolic tangent |
x̂ | unit vector, x hat |
∥ | parallel |
⟂ | perpendicular |
x | mean, average, antiparticle, x bar |
x̃ | median, supersymetric particle, x tilde |
⟨⟩ | time average, ensemble average, bracket |
p(x) | probability distribution, probability density function |
∆ | increment, change, delta |
d | differential, d |
∂ | partial differential, d partial, del |
ẋ | time rate of change, first derivative with respect to time, x dot |
ẍ | second derivative with respect to time, x double dot |
x⃛ | third derivative with respect to time, x triple dot |
∇ | gradient, grad, del, nabla |
∇ · | divergence, div, del dot |
∇ × | curl, del cross |
∇2 | laplacian, del squared |
∑ | summation, sigma |
∫ | integral |
∬ | double integral |
∭ | triple integral |
∮ | contour integral |
∯ | surface integral |
∰ | volume integral |
∞ | infinity |
ℵ0 | transfinite number, aleph null |
Greek alphabet (with variants) letter | English name | letter | English name |
Α, α | alpha | Ν, ν | nu |
Β, β, ϐ | beta | Ξ, ξ | xi |
Γ, γ | gamma | Ο, ο | omicron |
Δ, ∆, δ | delta | Π, ∏, π, ϖ | pi |
Ε, ε, ϵ | epsilon | Ρ, ρ, ϱ | rho |
Ζ, ζ | zeta | Σ, ∑, σ, ς | sigma |
Η, η | eta | Τ, τ | tau |
Θ, ϴ, θ, ϑ | theta | Υ, υ | upsilon |
Ι, ι | iota | Φ, φ, ϕ | phi |
Κ, κ, ϰ | kappa | Χ, χ | chi |
Λ, λ | lambda | Ψ, ψ | psi |
Μ, μ, µ | mu | Ω, Ω, ω | omega |
Astronomical symbols symbol | celestial body | symbol | constellation |
☉ | Sun | ♈ | Aries |
☿ | Mercury | ♉ | Taurus |
♀ | Venus | ♊ | Gemini |
♁ | Earth | ♋ | Cancer |
☽, ☾ | Moon | ♌ | Leo |
♂ | Mars | ♍ | Virgo |
♃ | Jupiter | ♎ | Libra |
♄ | Saturn | ♏ | Scorpius |
♅, ⛢ | Uranus | ♐ | Sagittarius |
♆ | Neptune | ♑ | Capricorn |
♇, ⯓ | Pluto | ♒ | Aquarius |
⚳ | Ceres | ♓ | Pisces |
Musical symbols symbol | name |
♭ | flat, semitone lower |
♮ | natural, no semitone adjustment |
♯ | sharp, semitone higher |