The SI System
or
How to Know “How Much?”
The Metric System
• Officially called the SI System
• Based on increments of 10 (one decimal place or
zero)
• A good measurement has a number and a unit
• Prefixes on the unit name tell you how many zeroes to
put before or after a number
• Used in every country around the world except the
USA and Báhrain
• The official measurement system of the USA
since the late 1800s
Why you don’t already know the
Metric System
Your parents didn’t know it
No incentive for companies to switch
You are still being taught the Imperial
System through everyday experiences
- Recipes
- Consumer goods
There is a slow, steady inclusion process
Base Units
• Base units are defined by only one
measurement
Length
• Distance from one point to another
• Meters (m) are the base units (a little longer
than a yard)
• For smaller items, centimeters (about one knuckle), and millimeters (the
thickness of a dime) are used
Mass
• Amount of substance (number of particles)
in an object
• Gram (g) is the base unit
• It is too small for some common measurements
(about 1 paper clip of matter)
• Usually use the kilogram (kg) for basis of
comparisons
• A kilogram is a little more than 2 pounds
Time
• How long it takes for something to happen
• Also called “Time Elapsed” or “Elapsed Time”
• Seconds (s) are the base unit
• Can lead to large numbers (1hr = 3600s)
What would you use to measure the
length of your arm?
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0%
0%
0%
0%
Liters
Meters
Grams
Grams/Milliliter
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What would you use to measure how
much sugar is in one teaspoon?
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0%
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0%
0%
Liters
Meters
Grams
Kilograms
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What would you use to measure how
much you weigh?
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0%
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0%
0%
Liters
Meters
Grams
Kilograms
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What would you use to measure the
width of the room?
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0%
0%
0%
0%
Liters
Meters
Grams
Grams/Milliliter
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Participant Scores
500
500
Taylor Abbott
Ashlee Carlisle
400
300
Shawn Weerts
Angel Loper
500
500
500
Logan Chandler
Quanda Dickerson
Ivy Lopez
300
300
200
Junior Williams
Mercedes Matthieu
Shakira Griffin
500
500
500
500
Alora Nordstrom
Russ Partridge
Damien Van Pelt
Chantel Williams
400
Angelica Ocasio
Derived Units of the SI System
• Derived units are defined by two or more
measurements
• Volume
• Amount of space taken up by a substance
• Liters (L) are the base units (a little more than a quart)
• Liters are too large for some measurements, so
milliliters (mL) are often used
What would you use to measure how
much water is in a pool?
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0%
0%
0%
0%
Liters
Meters
Grams
Grams/Milliliter
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More Derived Units
• Density
• Amount of matter in an object divided by the space
taken up by the object
• “How much stuff is in how much space”
• Usually expressed in grams per milliliter (g/mL) for
smaller amounts
• Expressed in kilograms per liter (kg/L) for larger
amounts
• THE NUMBER DOES NOT CHANGE
SI Prefixes
• Used to show a number of base units
• Think of them as coefficients (multipliers)
• Easy to convert by sliding the decimal
SI Prefixes
•
•
•
•
•
From the largest to the smallest
kilo- hecto- deka- BASE deci- centi- milli1000 100 10
1 1/10 1/100 1/1000
“King Henry died by drinking chocolate milk.”
Put your finger on the unit you have, move it to
the unit you want
• Move your decimal the same number of places in
the same direction that your finger moved
Testing your knowledge…
• Answer the five questions…
• Use the “Metric Ruler” to slide the decimal
to get the desired units…
• Ready?
What is 25mm in m?
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2.5m
0.25m
0.025m
0.0025m
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How many grams are 1.12kg?
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112g
0.00112g
0.112g
1120g
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How many Liters are 591mL?
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0.591L
59.1L
0.059L
5.91L
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What is 2.5cm in mm?
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250mm
.25mm
25mm
0.025mm
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0.355L is how many mL?
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3.55mL
35.5mL
355mL
3550mL
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