The International System of Units

The Système International d'Unités, or International System of Units (abbreviated to S.I.) was adopted by Australia after the Eleventh General Conference on Weights and Measures in 1960.
The S.I. consists of units (7 base units, 2 supplementary units, various derived units), and the decimal multipliers for these units.

The base units are shown in the following table.

 quantity unit name symbol definition now based on: length meter m the wavelength of light from Krypton-86 mass kilogram kg a mass placed in Paris in 1889 time second s the time for an electron to move in an atom electric current Ampère A the force between two currents temperature Kelvin K 1/273.16 of triple point of water luminous intensity candela cd the light falling on an area amount of substance mole mol 0.012kg of Carbon-12

The supplementary units are

Derived units are numerous and will be explained as they are introduced. Some have special names, like frequency, force, and flux density.

A few examples of derived units

 quantity unit name symbol area square metre m2 volume cubic metre m3 density kilogram per cubic metre kg.m-3 speed metres per second m.s-1

There are some units in popular or professional use, which are outside this system.
Some examples of these are: centimetre, hectopascal, hectare, kilometre per hour etc.
In this course, non standard units should be automatically converted before use.
Replace each non-standard unit with its size in standard units then separate out the units and simplify.

Example:
5 c.c. = 5 cm3 = 5 x (10-2 m)3 = 5 x 10-6 m3
72 km/hr = 72 (1000 m)/(3600 s) = 72 x (1/3.6) m.s-1 = 20 m.s-1

The following decimal prefixes are based on multiples of 1000.
The full table is shown, but usually only the prefixes between Tera and pico are used.

 Prefix Symbol Multiplier 10+0 = 1 Prefix Symbol Divisor kilo k 10+3 milli m 10-3 Mega M 10+6 micro µ (Gk: mu) 10-6 Giga G 10+9 nano n 10-9 Tera T 10+12 pico p 10-12 Peta P 10+15 femto f 10-15 Exa E 10+18 atto a 10-18 Zetta Z 10+21 zepto z 10-21 Yotta Y 10+24 yocto y 10-24

Standard form is a number between 1 and 10 multiplied by the appropriate power of ten, e.g. 3.1 x 10-4 m.
Ternary form uses only the prefixes above and is the preferred form for this course, e.g. 310 µm.

Significant figures give the number of digits which establish the accuracy of the measurement.
For example, if the average radius of the Earth is given as 6360 km, this implies that the measurement is meaningful only to 10s of km. Calculators give all the digits they can display, so calculator results should have the number of digits reduced to show the accuracy of the result. The last digit should be rounded up (if the next digit is 5 or greater) or left as is (if the next digit is less than 5). email Write me a note if you found this useful