Metric System
Measurements in science
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Why do scientists need a standard system of measurements?
–
Remember that science must be repeatable – another
scientist has to able to repeat your experiment using the
same amounts, concentrations, lengths, weights, etc.
•
Why do scientists use the metric system rather than an
alternate set of standards?
•
There are two problems with other measurement systems:
1. The
units are defined on imprecise and variable standards:
the length of your foot, the length on your arm, etc.
–
1 inch = width of your thumb
–
1 foot = length of your foot
–
1 yard = center of the body to your fingertips
2.
The division between increasing
units appears random and makes
no sense
–
–
–
Take for example the Imperial
(American Standard)
measurements for length (see
sidebar)
How about volume? Do you
know how much is in a Gill, Peck,
Strike, Chaldron, or Firkin?
12 inches = 1 foot
3 feet = 1 yard
22 yards = 1 chain
10 chains = 1 furlong
8 furlongs = 1 mile
5280 feet = 1 mile
1760 yards = 1 mile
How about mass – do you know how much a Mite,
Stone, Quarter, or Hundredweight weighs? The last
weighs 112 lbs in case you were wondering…
The metric system
•
•
The use of multiple systems did not become a problem until
the onset of intercontinental trade – it was impossible to
know what your system of measurements converted into
another country’s system
Around 1800, the French decided that a new system of units
was needed to allow traders to know what they were getting –
this system:
– would be based on unvarying quantities in nature so
anyone, anywhere on the planet, could generate a
reasonably accurate measurement of a standard
– would derive all it’s units from a base unit rather than use a
bunch of silly names for different amounts of one physical
aspect
– would be decimal – each step up or down in unit would vary
by a factor of 10, not some random factor
The metric system: units
•
The new system was called the Metric System (or SI) - the
metric units were defined in an elegant way unlike any
traditional units of measure
•
The Earth itself and other physical properties were used to
provide base standards so everyone, anywhere, could define
the unit
–
Units for length and distance - the meter was defined to be
one ten-millionth of the distance from the Equator to the
North Pole
–
Units for volume - the liter was to be the volume of one
cubic decimeter (10 x 10 x10 cm)
–
Units for mass (weight) - the kilogram was to be the weight
of a liter of pure water
The metric system: units (cont.)
–
•
Units for Temperature - degree Celsius, 0°C is the freezing
point of pure water, 100°C is the boiling point of pure water
Each measurement would include the base unit so you know
what physical aspect is being measured – the prefix would tell
you which factor of 10 to multiply or divide the base unit
Prefix
5 kilo-meters (km)
Kilo translates to
1000 – just multiply
the base unit by
1000 (103 in
scientific notation)
The base unit, a
measurement of
length in this case
Symbol
Multiplier
Giga
G
109
Mega
M
106
Kilo
k
103
Centi
c
10-2
Milli
m
10-3
Micro
m
10-6
Nano
n
10-9
Measurements during this course
•
•
During this course, you will measure mass, volume, length
and temperature – your instructor will give a quick
demonstration on the typical equipment used in the lab to
determine these physical measurements including:
–
Scales – balance beam and electronic
–
Pipettes and graduated cylinders
–
Meter rulers
–
Thermometers
You must also be able to use scientific notation and to be
able to convert metric measurements between different
multipliers (see lab notebook and extra handout)
Practice
Metric Conversions
Ladder Method
Ladder Method
1
2
KILO
1000
Units
3
HECTO
100
Units
DEKA
10
Units
DECI
0.1
Unit
Meters
Liters
Grams
How do you use the “ladder” method?
1st – Determine your starting point.
2nd – Count the “jumps” to your ending point.
3rd – Move the decimal the same number of
jumps in the same direction.
CENTI
0.01
Unit
MILLI
0.001
Unit
4 km = _________ m
Starting Point
Ending Point
How many jumps does it take?
4. __. __. __. = 4000 m
1
2
3
Conversion Practice
Try these conversions using the ladder method.
1000 mg = _______ g
1 L = _______ mL
160 cm = _______ mm
14 km = _______ m
109 g = _______ kg
250 m = _______ km
Compare using <, >, or =.
56 cm
6m
7g
698 mg
Metric Conversion Challenge
Write the correct abbreviation for each metric unit.
1) Kilogram _____
4) Milliliter _____
7) Kilometer _____
2) Meter _____
5) Millimeter _____
8) Centimeter _____
3) Gram _____
6) Liter _____
9) Milligram _____
Try these conversions, using the ladder method.
10) 2000 mg = _______ g
15) 5 L = _______ mL
20) 16 cm = _______ mm
11) 104 km = _______ m
16) 198 g = _______ kg
21) 2500 m = _______ km
12) 480 cm = _____ m
17) 75 mL = _____ L
22) 65 g = _____ mg
13) 5.6 kg = _____ g
18) 50 cm = _____ m
23) 6.3 cm = _____ mm
14) 8 mm = _____ cm
19) 5.6 m = _____ cm
24) 120 mg = _____ g
Compare using <, >, or =.
25) 63 cm
26) 536 cm
6m
53.6 dm
27) 5 g
28) 43 mg
508 mg
5g
29) 1,500 mL
30) 3.6 m
1.5 L
36 cm
Tutorial
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http://www.wisconline.com/objects/ViewObject.aspx?ID=ABM2301
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Scientific Notation
http://www2.fiu.edu/~graphing/purpose.htm
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Graph tutorial
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http://www.quia.com/rr/96635.html
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Millioniare game on MS