# 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