Standards of measurement require agreed upon units for comparison. The International System of Units (SI) is the standard system used by most nations, with base units for length, mass, time, and other quantities. SI units include the meter for length, kilogram for mass, second for time, and kelvin for temperature. The appropriate unit depends on the size of the item measured, with smaller objects often measured in centimeters, grams or other decimal units.
2. Units and Standards
• In order for a measurement to be useful, a
measurement standard must be used.
• A standard is an exact quantity that people
agree to use for comparison.
3. Measurement Systems
Suppose the length of a
string in a ball of yarn is
100. Can you tell how
much string is in the ball?
NO!!
• It could be 150 feet, 150 meters, or some
unit you’ve never heard of.
• In order for a measurement to make sense
it must have a number and a unit.
4. International System of Units
• In the U.S. we buy milk by the gallon, potatoes
by the pound, and lumber by the foot.
• These are a part of the English system of
measurement.
• Most other nations use a system of
measurement based on multiples of ten.
• This is known as the International System of
Units or SI.
5. Common SI Prefixes
Prefix Symbol Multiplying Factor
Kilo- k 1000
Deci- d 0.1
Centi- c 0.01
Milli- m 0.001
Micro- m 0.000001
Nano- n 0.000000001
6. Using SI Units
• Every type of quantity measured in SI
has a base unit and a symbol for that
unit.
7. SI Base Units
Quantity Measured Unit Symbol
Length Meter m
Mass Kilogram kg
Time Second s
Electric current Ampere A
Temperature Kelvin K
Amount of
substance
Mole mol
Intensity of light Candela cd
8. Length
• The SI base unit for length is the meter (m).
• Remember: SI is based on powers of ten
• Therefore:
1m=10dm=100cm=1000mm
• Metric rulers and meter sticks are used to
measure length.
9. Choosing a Unit
• The size of the unit you use to measure with
will depend on the size of the item being
measured.
1 meter 1
centimeter
10 football fields=
1 kilometer
10. Volume
• The amount of space occupied by an object.
• Volume= length x width x height
• V= 3cm x 3cm x3cm
• V= 27cm
3 cm
3 cm
3cm
3
11. Mass
• Measurement of the matter in an object.
• Base unit: kilograms (kg)
• Grams (g) and milligrams (mg) are used for
measuring objects of small mass.
Which ball has
more mass?
How manygrams are inone kilogram?
12. Density
• Density is the mass per unit of volume of a
material. (Expressed as grams per cubic cm)
• D=m/v
A cube of silver would be more dense than a cube of
aluminum, even if they were the same size!!
13. Time and Temperature
• The SI unit for time is the second (s).
• The SI unit for temperature is the Kelvin (K).
• 0 degrees K is the COLDEST possible
temperature, also known as absolute zero.
That is -273 degrees Celsius,
which is 273 degrees below
freezing!!
14. Summary
• A standard is an exact quantity that people agree to use for comparison.
• In order for a measurement to make sense it must have a number and a
unit.
• The International System of Units or SI is a system of measurement based
on units of 10 and used by most nations around the world.
• Every type of quantity measured in SI has a base unit and a symbol for
that unit.
• The SI base unit for length is the meter (m).
• The size of the unit you use to measure with will depend on the size of the
item being measured.
• Volume= length x width x height
• Mass is the measurement of the matter in an object (kg).
• Density is the mass per unit of volume of a material. (Expressed as grams
per cubic cm)
• The SI unit for time is the second (s).
• The SI unit for temperature is the Kelvin (K).
