Drawing scientific conclusions - OCR 21st CenturyUsing units
It is important to process and present data in a way that makes it easy to analyse. It is also important to evaluate the quality of data before drawing a conclusion.
Scientists use the International System of Units - SI unitInternationally agreed system of measurements - Système Internationale d'Unités.. The table shows some common units.
Quantity
Unit name
Unit symbol
Length
metre
m
Mass
kilogram
kg
Time
second
s
Temperature
degree Celsius
°C
Pressure
pascal
Pa
Energy
joule
J
Current
amp
A
Quantity
Length
Unit name
metre
Unit symbol
m
Quantity
Mass
Unit name
kilogram
Unit symbol
kg
Quantity
Time
Unit name
second
Unit symbol
s
Quantity
Temperature
Unit name
degree Celsius
Unit symbol
°C
Quantity
Pressure
Unit name
pascal
Unit symbol
Pa
Quantity
Energy
Unit name
joule
Unit symbol
J
Quantity
Current
Unit name
amp
Unit symbol
A
Prefixes
Scientists measure a wide range of quantities, some very large and some very small. Measurements for different order of magnitudeAn order of magnitude estimate approximates a number to the nearest power of ten. have specific prefixes:
Prefix name
Prefix symbol
Factor
Power
tera
T
1,000,000,000,000
×1012
giga
G
1,000,000,000
×109
mega
M
1,000,000
×106
kilo
k
1,000
×103
centi
c
0.01
×10-2
milli
m
0.001
×10-3
micro
μ
0.000 001
×10-6
nano
n
0.000 000 001
×10-9
Prefix name
tera
Prefix symbol
T
Factor
1,000,000,000,000
Power
×1012
Prefix name
giga
Prefix symbol
G
Factor
1,000,000,000
Power
×109
Prefix name
mega
Prefix symbol
M
Factor
1,000,000
Power
×106
Prefix name
kilo
Prefix symbol
k
Factor
1,000
Power
×103
Prefix name
centi
Prefix symbol
c
Factor
0.01
Power
×10-2
Prefix name
milli
Prefix symbol
m
Factor
0.001
Power
×10-3
Prefix name
micro
Prefix symbol
μ
Factor
0.000 001
Power
×10-6
Prefix name
nano
Prefix symbol
n
Factor
0.000 000 001
Power
×10-9
Converting units
To convert between a unit with difference prefixes, multiplication or division of the right factor of ten (10, 100, 1,000) is used.
Always do a sense check when multiplying or dividing and ask, “Is the answer expected to be larger or smaller?”
Question
Convert 5 cm into mm.
1 cm = 10 mm so the conversion is ×10
5 × 10 = 50 mm
This is what would be expected because millimetres are smaller than centimetres.
Time is dealt with differently if it is recorded in minutes, as this is not an SI unit:
