The Metric System and Units of
Measurement
Units
• After measuring a value, you MUST assign
proper units!!
• “Walk five in that direction” means nothing
until you provide a unit... meters, feet, etc.
• In science, we will use the Metric System or
the SI system
The SI System, Units of Measurement
Quantity
SI derived unit (symbol)
Quantity
SI derived unit (symbol)
Length
Meter (mm, cm, m)
Time
Seconds (s)
Volume
Liters (mL, cm3, m3)
Pressure
Pascal (Pa, kPa)
Mass
Grams (g, kg, mg)
Energy
Joules (J)
Density
Mass per unit of volume
Ex: g/mL, g/cm3, kg/m3
Amount of
Substance
Moles (mol)
Temperature Kelvins (K), 0⁰C = 273.15 K
The SI System of Measurement
• The SI System uses many prefixes to increase
or decrease the size of the values
• A KILOmeter is greater than a meter which is
greater than a MILLImeter
• The prefixes allow us to work with very large
numbers or very small numbers while still
working with manageable sized values.
Prefix
Abbreviation
Value (Base Unit)
Kilometer
km
1000
Hectometer
hm
100
Dekameter
dam
10
Base Unit (meter)
meter
1
Decimeter
dm
0.1
Centimeter
cm
0.01
Millimeter
mm
0.001
Micrometer
µm
0.000001
Nanometer
nm
0.000000001
Units of Mass / Weight
• Mass is NOT weight
• Review: What is mass? What is weight??
• Mass uses units of grams, whiles weight is
usually measured in pounds
Concept Check
• Name the quantity measured by each of the
following SI units and give the SI symbol of the
unit.
– mole
– grams/millileter
– second
– kilograms/cubic meter
--- pascal
--- meter
--- kilogram
--- Kelvins
Concept Check
• What is the difference between mass and
weight.
• What is the symbol and meaning of each
prefix
– milli– nano-
--- deci--- centi-
Calculations
• Calculate the volume of a book that is 21 cm
tall, 12 cm wide, and 3.5 cm thick
• Calculate the density of a sample with a mass
of 12.51 grams and a volume of 17.5 cm3
Calculations
• What is the percent error of a measurement
with the experimental value of 18.99 grams
and an accepted value of 15.890 grams?
Specific Gravity
• Specific Gravity is a comparison of the density
of a substance with the density of a reference
substance, usually at the same temperature.
• This “reference substance” is usually _______.
• Specific Gravity = density of substance (g/cm3)
density of H2O (g/cm3)
Specific Gravity
• Specific Gravity = density of substance (g/cm3)
density of H2O (g/cm3)
• The specific gravity of a liquid can be
measured using a device called a hydrometer
• The density of H2O is 1.00g/cm3 (at room
temp), making a substances’ specific gravity
equal to its own density at room temp.
Practice
• How is density calculated?
• What are the three equations relating mass,
volume, and density?
Practice
• A weather balloon is inflated to a volume of 2.2x103 L
with 37.4 grams of He. What is the density of the
helium in g/L?
• A plastic ball with a volume of 19.7cm3 has a mass of
15.8 g. What is the density? Would this ball sink or
float in a container of gasoline (d=0.66g/cm3)
Temperature Scales
• The Temperature of an object determines the
direction of heat transfer
• Heat travels from ________ to ________.
• All substances (except water) expand when
heated and condense when cooled. What
happens to the pressure??
HEAT THEM UP,
SPEED THEM UP!!!
Temperature Scales
• Fahrenheit
• Celsius
• Kelvin
Conversion Equations
⁰F = (⁰C * 9/5 ) + 32
⁰C = (⁰F – 32 ) * 5/9
K = ⁰C + 273.15K