Units of Measurement and Terminology


Units of Measurement


Scientific measurements almost exclusively use the metric system. Each variable - mass, length, time, has a base unit in which everything is measured. They are then given prefixes to make the numbers easier to work with in calculations or conversation.

Name
Symbol
Scientific Notation
Adjustment Factor
exa
E
1018
1,000,000,000,000,000,000
peta
P
1015
1,000,000,000,000,000
tera
T
1012
1,000,000,000,000
giga
G
109
1,000,000,000
mega
M
106
1,000,000
kilo
k
103
1,000
hecto
h
102
100
deka
da
101
1
deci
d
10-1
.1
centi
c
10-2
.01
milli
m
10-3
.001
micro
ų
10-6
.000001
nano
n
10-9
.000000001
pico
p
10-12
.000000000001
femto
f
10-15
.000000000000001
atto
a
10-18
.000000000000000001

Mass - The base unit of measurement in Canada is the gram. This is about the weight of a dime. If we had 1000 dimes, it would weigh 1 kg.

Likewise, it we had 1 gram of mercury, we would have 1000 mg, or 1,000,000 ųg of mercury.

Volume - The base unit of measurement of volume in Canada is the litre.

If we had one litre of water, we would have 1000 mL.

Likewise, if we had 1 mL of water, we would have .001 L of water.

Concentration - A concentration is the relationship between the amount of a substance you have, and the space you're fitting it into. For materials dissolved in water, the concentration is usually given as mg/L, but many other systems exist.

To draw an example from the Health Canada guidelines for water contaminants, the Maximum Allowable Concentration for mercury is 0.001 mg/L. This means that for every litre of water, there should be no more than 0.001 mg, or 0.000001 grams of mercury.

More concentration - Another common form of expressing concentration is parts-per-million (ppm) or parts-per-billion (ppb). Unlike mg/L, however, ppm and ppb are relationships between the two things, usually the solute and the solvent, rather than an explicit value.

A 1 ppm concentration of sugar in your coffee would mean that there is one sugar molecule for every million coffee "molecules".

For trivia night, the lowest concentration at which most people can taste chlorine in their water is 0.156 ppm.