Mechanical Engineering Symbols, Meaning and Its SI Units and/or Value

As you are a regular reader of this blog, in order to provide you a clear meaning and understanding of our articles under Mechanical Engineering, you need to know the symbols we have used in rest of the articles. It is almost impossible to use the full meaning of symbols each and every place and degrade the value of universal symbols what they stand for. So, in the beginning of our session, we have listed the common symbols (which most of you are aware of) are provided for the easy understanding and reference purpose. you can refer these symbols for all the articles under section Mechanical Engineering for better understanding. Furthermore, there are some symbols which carry more than one meaning. You need to take care of these while going through and draw the correct meaning of it.

A tool tip from the writer, when you read the Mechanical Engineering articles, we will make sure that, we provide a link at the beginning of the article of this page so that you have easy access to this page and refer seamlessly without much hitch.

Below are the symbols which are being used in all the articles about Mechanical Engineering.

Symbol	Meaning	SI units and/or value
A	Area	m2
BTU	British Thermal Unit	1 BTU = 1055 J
CD	Drag coefficient	---
CL	Lift coefficient	---
CP	Specific heat at constant pressure	J/kgK
CV	Specific heat at constant volume	J/kgK
c	Sound speed	m/s
COP	Coefficient Of Performance	---
d	Diameter	m (meters)
E	Energy	J (Joules)
E	Elastic modulus	N/m2
e	Internal energy per unit mass	J/kg
F	Force	N (Newtons)
f	Friction factor (for pipe flow)	---
g	Acceleration of gravity	m/s2 (earth gravity = 9.81)
gc	USCS units conversion factor	32.174 lbm ft/ lbf sec2 = 1
h	Convective heat transfer coefficient	W/m2 K
I	Area moment of inertia	m4
I	Electric current	Amps
k	Boltzmann’s constant	1.380622 x 10-23 J/K
k	Thermal conductivity	W/mK
L	Length	m
M	Molecular Mass	kg/mole
M	Moment of force	N m (Newtons x meters)
M	Mach number	---
m	Mass	kg
ṁ	Mass flow rate	kg/s
N	Number of moles	---
NA	Avogadro’s number (6.0221415 x 1023)	---
P	Pressure	N/m2
P	Point-load force	N
Q	Heat transfer	J
q	Heat transfer rate	W (Watts)
ℜ	Universal gas constant	8.314 J/mole K
R	Mass-based gas constant = ℜ/M	J/kg K
R	Electrical resistance	ohms
Re	Reynolds number	---
r	Radius	m
S	Entropy	J/K
T	Temperature	K
T	Tension (in a rope or cable)	N
t	Time	s (seconds)
U	Internal energy	J
u	Internal energy per unit mass	J/kg
V	Volume	m3
V	Voltage	Volts
V	Shear force	N
v	Velocity	m/s
W	Weight	N (Newtons)
W	Work	J
w	Loading (e.g. on a beam)	N/m
Z	Thermoelectric figure of merit	1/K
z	elevation	m
α	Thermal diffusivity	m2 /s
γ	Gas specific heat ratio	---
η	Efficiency	---
ε	Strain	---
ε	Roughness factor (for pipe flow)	---
µ	Coefficient of friction	---
µ	Dynamic viscosity	kg/m s
θ	Angle	---
ν	Kinematic viscosity = µ/ρ	m2 /s
ν	Poisson’s ratio	---
ρ	Density	kg/m3
ρ	Electrical resistivity	ohm m
σ	Normal stress	N/m2
σ	Stefan-Boltzmann constant	5.67 x 10-8 W/m2 K4
σ	Standard deviation	[Same units as sample set]
τ	Shear stress	N/m2
τ	Thickness (e.g. of a pipe wall)	m

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