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Physics Symbols

What is the Importance of Physics Symbols?

In physics, there are a large number of physical quantities we include while performing calculations. To make it more convenient for users and easier to use and remember, we often use notations/symbols to represent these physical quantities. These notations/symbols we use to represent physical quantities when solving problems related to them or for other purposes are symbols.


In physics, we symbolise everything with an English/Greek alphabet, such as for the speed of light, wavelength, velocity, and so on.


Let us assume that a lady drives her car at a speed of 30 kmph and reaches her hometown in 2 hrs and if she drives at 50 kmph, she reaches in 1.5 hr. So, if we have to represent these units as symbols, how can we do that?


In this article,  you will find the most popular physics symbols and also those we commonly use in physics with their names, the type of quantities along with their respective units in tabular format. 


Examples of Physical Symbols

Also, the symbols used for physical quantities are vastly different. Sometimes, the symbol may be the first letter of the physical quantities they represent, like ‘d’, which stands for distance. Other times, they may be completely unrelated to the name of the physical quantities, such as c symbolises the speed of light. They may also be in the form of Greek characters, like λ, which stands for wavelength.


Below is an elaborated list of the most commonly used list of symbols in physics with their SI units. Please note that a particular symbol might relate to more than one quantity.


Symbols for Physical Quantities Related to Space and Time


Symbols

Quantity/ Coefficients

S.I. Unit

Physical Quantity (Scalar/Vector)

r

Radius, the radius of curvature

Metre

Functions as both scalar and vector

s

Displacement

Metre

Vector

d

Distance

Metre

Scalar

θ

Angular displacement, 

Radian

Vector

φ

The rotational angle

Radian

A uniquely-defined magnitude and direction, but is not a vector quantity.

(Does Not obey commutative law)

x, y, z

Cartesian Coordinates

Unitless

Scalar

î, ĵ, k̂

Cartesian unit vectors

Unitless

Vector

r, θ, φ

Spherical coordinates

Metre/Radian

Vector

r̂, θ̂, φ̂

Spherical vectors

Unitless

Vector

r, θ, z

Cylindrical coordinates

Metre/Radian

Scalar

r̂, θ̂, ẑ

Cylindrical vectors

Unitless

Vector

Normal vector

Unitless

Vector

Tangential unit vector

Unitless

Vector

h

Height, Depth

Metre

Scalar

ℓ, L

Length

Metre

Scalar 

t

Time

Second 

Scalar

D (= 2 r)

Diameter

Metre

Scalar

C

Circumference

Metre

Scalar 

A

Area

Square Metre

Functions as both scalar and vector (like Area vector in a magnetic flux formula)

V

Volume 

Cubic Metre (m3)

Scalar

τ

Time Constant

Second (s)

Scalar

T

Periodic time

Second (s)

Scalar 

f

Frequency 

1/second or (1/s)

Scalar 

ω

Angular frequency

Rad/s

Scalar


Below are some symbols that are used frequently in physics with their names, the type of quantities and their respective SI units in tabular format.


Physics Symbols Related to Mechanics


Symbols

Quantity/ Coefficients

S.I. Unit

Physical Quantity (Scalar/Vector)

v

Velocity, speed

metre/second (m/s)

Speed = Scalar

Velocity = vector

a

Acceleration

metre/square second (m/s2)

Vector 

g

Acceleration due to gravity

metre/square second 

Vector 

ac

Centripetal/Centrifugal acceleration

metre/square second

Vector 

m

Mass

Kilogram (kg)

Scalar 

F

Force

Newton (N)

Vector

W/Fg

Force due to gravity/Weight

Newton

Vector

Fg/ N

Normal force

N

Vector

Ff

Force of friction

N

Vector

µ

Coefficient of friction

Unitless

Scalar

p

Momentum

Kg.m/s

Vector

J

Impulse

N/s

Vector

E

Energy

Joule  (J)

Scalar

Kinetic energy

J

Scalar

U

Potential Energy

J

Scalar

Vg

Gravitational potential

J/kg

Scalar

η

Efficiency

Unitless

Scalar

P

Power

Watt

Scalar

α

Rotational acceleration

Radian per second squared (Rad/s2)

Vector

ω

Rotational velocity 

Rad/s

Vector

τ

Torque

N/m

Vector

L

Angular momentum

Kilogram meter squared per second


Kg.m2/s

Vector

ρ

Density

Volume 

Mass density

Kilogram per cubic meter

Scalar 

I

Moment of inertia

Kg.m2

Scalar


Physical Symbols Related to Fluid Mechanics


Symbols

Quantity/ Coefficients

S.I. Unit

Physical Quantity (Scalar/Vector)

λ

Linear mass density

kg/m

Scalar

σ

Area mass density

Kilogram per square meter (kg/m2)

Scalar 

FB, B

Buoyancy

N

Vector

qm

Mass flow rate

kg/s

Scalar

qV

Volume flow rate

m3/s

Scalar

FD, R

Drag or air resistance

N

Vector

CD

Drag Coefficient

Unitless

Scalar 

η

Viscosity

Pascal-second

Scalar

v

Kinematic Viscosity

m2/s

Scalar 

σ

Area mass density

kg/m2

Scalar

Re

Reynolds number

Unitless

Scalar

Fr

Froude number

Unitless

Scalar 

Ma

Mach number

Unitless

Scalar


Symbols Related to Solid Mechanics


Symbols

Quantity/ Coefficients

S.I. Unit

Physical Quantity (Scalar/Vector)

P

Pressure 

Pascal

Or

N/m2

Scalar 

σ

Stress

Pascal

Scalar 

τ

Shear stress

Pascal

Scalar

k

Spring constant

N/m

Scalar

E

Young’s modulus of elasticity

Pascal

Scalar 

G

Shear modulus of rigidity

Pascal

Scalar

ε

Linear strain

Unitless 

Scalar 

γ

Shear strain

Unitless

Scalar 

θ

Volume strain

Unitless 

Scalar 

S

Surface Tension 

N/m

Scalar 

K

Bulk modulus of compression

Pascal

Scalar 


Physical Quantities Related to Thermal Physics


Symbols

Quantity/ Coefficients

S.I. Unit

Physical Quantity (Scalar/Vector)

k

Thermal conductivity

W/m.K

Scalar 

P

Heat flow rate

Watt

Scalar

N

Number of particles

Unitless 

Scalar 

n

Amount of substance

Mole

Scalar

L

Latent heat/specific latent heat

J/kg

Scalar 

c

Specific heat capacity

J/kg. K

Scalar 

Q

Heat

J

Scalar 

Volume expansivity, coefficient of volume thermal expansion

1/K (inverse Kelvin)

Scalar 

α

Linear expansivity, coefficient of thermal expansion

1/K (inverse Kelvin)

Scalar 

T

Temperature 

Kelvin

Scalar 


Physical Symbol Related to Wave and Optics


Symbol

Quantity/Coefficients

S.I Unit

Physical Quantity (Scalar/Vector)

M

Magnification

Untiless 

Scalar 

f

Focal length

Metre 

Scalar 

n

Index of refraction

Unitless 

Scalar 

L

Level

Decibel (dB), decineper

Scalar 

I

Intensity

W/m2

Scalar

v, c

Wave speed

m/s

Scalar 

λ

Wavelength

Metre (m)

Scalar 

P

Power of a lens

Dioptre (D)

Scalar 


Physics Symbols Related to Electricity and Magnetism


Symbol

Quantity/Coefficients

S.I Unit

Physical Quantity (Scalar/Vector)

Poynting vector, intensity

W/m2

Vector 

η

Energy density

J/m3

Scalar 

n

Turns per unit length

1/m

Scalar 

N

Number of turns

Unitless 

Scalar

φB

Magnetic flux 

Weber

Vector

Magnetic field

Tesla

Vector 

FB

Magnetic force

N

Vector 

σ

Conductivity

Siemens/m 

(S/m)

Scalar 

G

Conductance 

Siemens

Scalar 

ρ

Resistivity

Ohm-m

Scalar 

R, r

Electric resistance/internal resistance

Ohm 

Scalar 

I

Electric current

Ampere (A)

Scalar 

ϵ

Dielectric constant

Unitless

Scalar 

Electromotive Force

Volt (V)

Scalar

C

Capacitance

Farad (F)

Scalar 

V

Voltage, electric potential

V

Scalar 

UE

Electric potential energy

J

Scalar 

φE

Electric flux 

Newton meter squared per coulomb (N/m2.C)

Vector 

E

Electric field 

N/C or V/m

Vector 

FE

Electrostatic force

N

Vector 

λ

Linear charge density

kg/m

Scalar 

σ

Area charge density

kg/m2

Scalar 

ρ

Volume charge density

kg/m3

Scalar 

q, Q

Electric charge

Coulomb (C)

Scalar 


Symbols Used in Modern Physics


Symbol

Quantity/Coefficients

S.I Unit

Physical Quantity (Scalar/Vector)

D

Dose/ dose absorbed

Gray (Gy)

Scalar

t1⁄2

Half-life

Second

Vector

ψ(r,t), ψ(r)φ(t)

Wave function 

Unitless 

Scalar

Work function

J

Scalar

H

Effective Dose

Sievert

Scalar

Γ

Lorentz factor/Lorentz gamma

Unitless

Scalar


From the above text on physics symbols, we understand that in Physics, we use various symbols or notations to denote different quantities. The denotations make the representation of the quantities easier.


It was also interesting to see that some physics symbols were very relatable (like “d” for distance) while some were unrelatable (like “c” for the speed of light or “λ” for wavelength). Also, we noticed that a particular symbol was related to more than one quantity.

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