Measurements Basic Principle of Measurements Part 1: Basic Principle of Measurements 10/11/2015.
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Transcript of measurements
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
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).