1. Physical Quantities & Units
Physical Quantities and Units refer to measurement.
Measurement involves counting, but we can only count numbers 1,2,3,4... of a particular item.
- The other thing we can do is to count the number of times a physical quantity is greater or less for one case than in another case.
- A complete specification of the method of counting specifies a unit.

2. How units are defined
- A unit has to have a special name and symbol. The usefulness of a unit is as a means of communicating to everyone who does science how it was particularly defined.
- To make a desk of a certain length, breath and height it is necessary to determine ratio of its dimensions as compared to the defined unit. ie. A numerical magnitude x its unit
Therefore, defined units must be:
- unambiguously defined
- reproducible to a great accuracy
- accepted by the most people

3. SI units
- The SI units (adopted in 1960) represent a set of basic physical quantities.
- Second(s). The second is defined as a number of the period of vibration of radiation from the cesium-133 atom.
- Metre (m). The distance travelled by light in vacuum during a time of 1/ second.
- Kilogramme (kg). Defined as the mass of a specific platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures in France.

4. SI Units
- Kelvin (K). The kelvin is defined as 1/ of the temperature of the triple point of water.
- Ampere (A). Defined as the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible cross section, and placed one metre apart in vacuum, would provide between the conductors a force equal to 2 x 10-7 newton per metre of length.
- Mole (mol). The amount of substance containing as many identical units as there are atoms in 12 grams of carbon-12.

6. Magnitudes METRIC SYSTEM PREFIXES Factor Decimal Representation Prefix
Symbol
1018
1,000,000,000,000,000,000
exa E
1015
1,000,000,000,000,000
peta P
1012
1,000,000,000,000
tera T
109
1,000,000,000
giga G
106
1,000,000
mega M
103
1,000
kilo k
102
100
hecto h
101 10
deka da 1
10-1
0.1
deci d
10-2
0.01
centi c
10-3
0.001
milli m
10-6
micro
10-9
nano n
10-12
pico p
10-15
femto f
10-18
atto a

7. Scalars and Vectors
Scalars are quantities which are fully described by a magnitude alone. Examples are all the SI base units which are all described by their numerical magnitudes.
Vectors are quantities which are fully described by both a magnitude and a direction.

8. Vectors & Resultant Vectors

9. Parallelogram method