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The official name of the International System of Units is Le Systeme International d'Unites, abbreviated SI. The basic units of SI are the metre, kilogram-mass and second. The unit of force is derived and is called the Newton. The units of the Newton are:

F = M*L/T^2 = (kilogram)*(metre)/(second)^2 = kg*m/s^2

The abbreviation for the Newton is N. The seven base units, with their symbols, are shown in Table 1-2. These are dimensionally independent. Lower case letters are used for the symbols unless they are derived from a proper name, then a capital is used for the first letter of the symbol. Note that the unit of mass uses the prefix kilo; this is the only base unit having a prefix.

Table 1-2 shows that the SI unit of temperature is the kelvin. The Celsius temperature scale (once called Centigrade) is not a part of SI but a difference of one degree on the Celsius scale equals one kelvin. A second class of SI units comproses the derived units, many of which have special names. Table 1-3 is a list of those we shall find most useful in our work in this ebook.

The radian (symbol rad) is a supplemental unit in SI for plane angle. A series of names and symbols to form multiples and submultiples of SI units have been established to provide an alternative to the writing of powers of 10. Appendix Table A-1 includes these prefixes and symbols.

Quantity Name Symbol ------------------------- -------- ------ Length metre m Mass kilogram kg Time second s Electric Current ampere A Thermodynamic Temperature kelvin K Amount of Matter mole mol Luminous Intensity candela cd ------------------------- -------- ------

Quantity Unit Symbol Formula ------------------------- ------------------------ ------ --------- Acceleration metre per second squared m*s^-2 Angular acceleration radian per second squared rad*s^-2 Angular velocity radian per second rad*s^-1 Area square metre m^2 Circular frequency radian per second (omega) rad*s^-1 Density kilogram per cubic metre kg*m^-3 Energy joule J N*m Force newton N kg*m*s^-2 Fource couple newton metre N*m Frequency hertz Hz s^-1 Power watt W J*s^-1 Pressure pascal Pa N*m^-2 Quantity of heat joule J N*m Speed revolution per second s^-1 Stress pascal Pa N*m^-2 Torque newton metre N*m Velocity metre per second m*s^-1 Volume cubic metre m^3 Work joule J N*m ------------------------- ------------------------ ------ ---------

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