THE SI SYSTEM

SI is an abbreviation for Systeme International and is a metric system of units that is being adopted internationally for all scientific and engineering work. This brief presentation presents only the aspects of the system per­tinent to this text.

Names of International Units

Physical Quanity

Name of Unit

Symbol

Length

Meter

m

Mass

Kilogram

kg

Time

Second

s

Electric current

Ampere

A

Temperature

Kelvin

К

DERIVED UNITS

Area

Square meter

rrr

Volume

Cubic meter

m3

Frequency

Hertz

Hz

(s")

Density

Kilogram per cubic meter

kg/m3

Velocity

Meter per second

m/s

Angular velocity

Radian per second

rad/s

Acceleration

Meter per second squared

m/s2

Angular acceleration

Radian per second squared

rad/s2

Force

Newton

N

(kg-m/s2)

Pressure

Newton per square metera

N/m2

Kinematic viscosity

Square meter per second

m2/s

Dynamic viscosity

Newton-second per square meter N-s/m2

Work, energy, quantity of heat

Joule

J

(N-m)

Power

Watt

W

(J/s)

Entropy

Joule per kelvin

J/K

Specific heat

Joule per kilogram kelvin

Jkg-‘K 1

Thermal conductivity

Watt per meter kelvin

Win ‘K 1

“I N/m2= I Pascal, denoted by Pa.

DEFINITIONS

newton (N) The newton is the force that gives a mass of 1 kg an acceleration of 1 m/s/s.

joule (J) The joule is the work done when the point of application of 1 N is displaced a distance of 1 m in the direction of force.

watt (W) The watt is the power that gives rise to the production of energy at the rate of 1 J/s.

Conversion Factors

Multiply By To Get

Newtons (N)

Meters (m)

Kilograms (kg)

Kilograms per cubic meter (kg/m3) Kilowatts (kW)

Pascals (Pa)

Pascals (Pa)

Meters per second (m/s)

Meters per second (m/s)

MISCELLANEOUS

g = 32.2 ft/sec2 = 9.81 m/s2 at sea level °K = °С+ 273.19 °R = °F +459.7 °С = (°F – 32)(5/9)

Universal Gas Constant (p = pRT)

R = 1716 ft2/s2/°R = 287.0 m2/s2/°K

PREFIXES

The names of multiples and submultiples of SI units may be formed by application of the following prefixes.

Factor by which unit is multiplied

Prefix

Symbol

1012

tera

T

109

giga

G

106

mega

M

103

kilo

к

102

hecto

h

10

deka

da

10~‘

deci

d

10~2

centi

c

10~3

milli

m

10~6

micro

p

io-9

nano

n

10~12

pico

p

10’15

femto

f

10 18

atto

a

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