Measurements and
Conversions
Grade 8
SI units
Read this sentence:
• ‘’When my son was 1 he walked 3, and when he was 4 he kicked his soccer
ball 8 and said his school was 5 away.’’
What does it mean?
Now read this sentence again:
• ‘’When my son was 1 year old he walked 3 steps, and when he was 4 years
old he kicked his soccer ball 8 meters and said his school was 5 minutes
away.’’
Units make ALL the difference!
SI units
• The most convenient system for science measurements is based on the
metric system
• It is called the International System of units or SI units
• SI units are a set of standard units agreed on by scientists throughout the
world!
• The most important SI units for you to know now is:
Quantity
Unit
Symbol
Length
Mass
Time
Temperature
Meter
Kilogram
Second
Kelvin
m
kg
s
K
Prefix multipliers
• Allow us to express a wide range of measurements in units that are similar
in size to the quantity we are measuring.
For example: To measure the diameter of a R5 coin, what
would be the best measurement to use?
• cm! Because a R5 coin is roughly 2.5cm in diameter
• If you were to measure the coin in km, that would mean that the coin would
be 0.000025km!!!
Pick a unit similar in size to (or smaller than) the quantity
you are measuring.
Prefix multipliers
• The SI system
uses prefix
multipliers with
the standard
units
Prefix
Symbol
Meaning
Multiplier
Notation
tera -
T
Trillion
1,000,000,000,000
1012
giga-
G
Billion
1,000,000,000
109
mega-
M
Million
1,000,000
106
kilo-
k
Thousand
1,000
103
hecto-
h
Hundred
100
102
deka-
da
Ten
10
101
base
-
-
-
-
Deci-
d
tenth
0,1
10-1
centi-
c
Hundredth
0,01
10-2
milli-
m
Thousandth
0,001
10-3
micro-
µ
Millionth
0,000001
10-6
nano-
n
Billionth
0,000000001
10-9
pico-
p
Trillionth
0,000000000001
10-12
femto-
f
quadrillionth
0,000000000000001
10-15
Converting between prefix multipliers
Unit
Kind Henry died miserably drinking chocolate marshmallow milk
Example: Convert 0.825m to mm
Step 1: Identify the unit
Meters
Step 2: Are you converting smaller or larger?
Smaller
Step 3: Move your decimal
Move 3 decimals to the right: 825mm
Arithmetic with units
1. Add /Subtract:
• Units stay the same
• Must be the same units!
2. Multiply:
• Units also multiply
3. Divide:
• Units also divide
1kg + 2kg = 3kg
5cm-1cm = 4cm
2m x 2m = 4m
2
5g / 5g = 1 (no units)
Conversion factors
Conversion factors
• Constructed from any 2 quantities known to be equivalent.
• It can be inverted because they are equal to 1 and the inverse of 1 is 1
E.g.
100cm 1000g 60 sec
;
;
1m
1kg 1 min
Formula:
• Information given x conversion factor = information sought
given unit x
desired unit
given unit
E.g. convert 5 hours to minutes
• 5 hours x
60 𝑚𝑖𝑛𝑢𝑡𝑒𝑠
1 ℎ𝑜𝑢𝑟
= 300 minutes
= desired unit