Some Important physics things (in no particular order)
Topics Covered
Units
and Measurements
Prefixes and Big numbers
Abbreviations for big and small numbers
m/s becomes ms-1
The
SI (International System) set of units is the modern metric set of units.
They all have a quantity and a unit.
The seven SI quantities are shown below.
|
QUANTITY
|
UNIT
|
Symbol
for Unit
|
|
length
|
meter
|
m
|
|
mass
|
kilogram
|
kg
|
|
time
|
second
|
s
|
|
electric
current
|
ampere
|
A
|
|
thermodynamic
temperature
|
kelvin
|
K
|
|
amount
of substance
|
mole
|
mol
|
|
luminous
intensity
|
candela
|
cd
|
All quantities can be expressed in terms of these quantities or combinations of these. For example Force is measured in Newtons but is a combination of mass, time and length (m·kg·s -2 )
More details can be found here
Many of the numbers in physics are either very big or very small, in order to avoid writing all these numbers in full as traditionally done a mathematical convention is used.
1000 = 1 x 10
1 000 000 = 1 x 10
6
1 000 000 000 = 1 x 10
9
0.001 = 1 x 10
-3
0.000001 = 1 x 10
-6
0.000000001 = 1 x 10
-9
All numbers in between just fit is as logic suggests!
245
000 = 2.45 x 10
5
0.000342 = 3.42 x 10
-4
Abbreviations for big and small numbers
Sometimes
abbreviations are used for big numbers. It is important to know these so you
don't make errors in calculations.
To make life simple we go up in threes!
The
following abbreviations are used. You will (should!) be familiar with some
of these.
10
-6
= micro
10
-3
= mili
10
3
= kilo
10
6
= mega
10
9
= giga
so 1000000 Joules of Energy = 1 x 10 6 Joules = 1 Mega joule = 1 MJ
There are more abbreviations but these are less common.
Traditionally speed is measured in meters per second and written as m/s. This convention is fine for simple expressions but as the physics gets more complicated then a clearer an more precise approach is needed. For all units a standard mathematical form is used. As well as maintaining a consistent approach it does make things easier to follow (when you get used to it!)
m/s
becomes m/s
-1
m/s
2
becomes m/s
-2
and so on
the square root of x is written as x 1/2