The Units in Short

To ensure that all students are starting at the same point, the first topic to be covered is the Internation System or Units, or SI. The SI specifies units to measure every conceivable quantity and a range of prefixes to help make these measurements more manageable.

The SI uses seven base units in terms of which all other units can be defined (although two of these, the candela and the metre, are now defined in terms of other base units, they are still know as such for historical reasons):

metre (m)

length

kilogram (kg)

mass

second (s)

time

ampere (A)

electrical current

kelvin (K)

absolute temperature

mole (mol)

quanity of matter

candela (cd)

luminous intensity

The three that we will use most frequently are the metre, the kilogram and the second.

In addition to the seven base units, there are numerous derived units so called because they are derived from the base units. The derived units we'll see include

joule (J)

energy, work

newton (N)

force

In addition to the seven base units and various derived units, the SI defines a number of prefixes to make it easier to deal with large and small numbers. Each prefix specifies an order of magnitude in the same way the exponent in scientific notation (which will be the topic of the next post) does. Thus one millimetre (1 mm) is 1x10-3 m, or 0.001 m. The prefixes we will likely encounter in this course are:

Prefix	Symbol	Exponent	Multiplier
tera	T	12	1 000 000 000 000
giga	G	9	1 000 000 000
mega	M	6	1 000 000
kilo	k	3	1 000
hecto	h	2	100
deca	da	1	10
		0	1
deci	d	-1	0.1
centi	c	-2	0.01
milli	m	-3	0.001
micro	µ	-6	0.000 001
nano	n	-9	0.000 000 001