Standards of Measurement

The International System of Units(SI)

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.

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.

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.

Common SI PrefixesPrefix 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

Using SI Units• Every type of quantity measured in SI has a base unit and a symbol for that unit.

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

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.

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

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 cm3cm

3

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 many grams are in one kilogram?

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!!

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!!

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).