SI Units
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In science, we need to speak the same
language
1795
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French scientists develop metric system
1960
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International committee meets to update
the system and names it the “Systeme
Internationale d’Unites” aka SI
SI Base Units
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Seven SI base units
Base unit
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A defined unit in a system of measurement that is based on
an object or event in the physical world
Tools of the Trade
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Mass Scale that measures GRAMS not POUNDS
 Pounds are used to measure the force of gravity on
your mass…we want to measure the amount of
STUFF (Matter) in a thing
Temperature thermometer measures the kinetic energy
(KE) /movement of particles
 Faster moving particle=more (KE)=higher temp
(HOT)
 Slower moving particles=less (KE)=cooler temp
(COLD)
Volume amount of space object takes up…
 ruler, measuring tape, etc to measure meters3 (l x w
x h)
 OR graduated cylinder to measure LITERS
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Measure volume at the MENISCUS (curve or dip in the
water)
SI Derived Units
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Not all quantities can be measured with base
units
More than one base unit can be used
Speed limit is measure in….
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MPH
Miles per hour
Which is a combo of what base units?
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Length and time
Derived Units
Common derived units we will use
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Speed
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Base unit of length and base unit of time
Meters/second
Volume
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3 base units of length
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Length x length x length
1 cm3 = 1 mL
Density
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Mass/volume
Ratio that compares mass of an object to its
volume
g/cm3 or g/mL
Density
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Density=mass divided by the
volume
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D=m/V
Gram/L or grams/m3
How do we figure out volume of
odd shaped objects…say a paper
clip?
Water Displacement
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What happens when you fill up the
bath tub to the rim and then get in?
Archimedes Principle
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Measure known amount of water in
graduated cylinder and record
VOLUME (mL)
 This is initial volume (Vi)
Drop in odd shaped object (paper clip)
Record the NEW volume of water
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Subtract Vi from Vf to get volume of
object (Vo)
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This is final vlume (Vf)
Vo = Vf- Vi
Get the mass of the paper clip form the
scale
Plug the mass (g) and volume (L) into
density formula to figure out the density
of the paper clip
Prefixes Used with SI units
Temperature
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SI unit?
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Our thermometers measure Celsius
To convert from Celsius to Kelvin
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Kelvin
0o C +
273 = 273 K
To convert from Kelvin to Celsius
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373 K -
273 = 100o C