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Chapter 2A & 2B - Units and Conversion Factors
Multiplication and Division of Units
Second power
Third power
miles/hours → “miles per hour”
ft × ft or ft2
ft × ft × ft or ft3
kilowatt hours → “kilowatt-hours”
Working with Units
Step 1: Identify the units in the problem. Use the units to decide how to approach the
solution and the units for the answer.
Step 2: Perform operations (such as multiplication or division) on both numbers and units.
But remember
(a) You cannot add or subtract numbers with different units. But you can combine
different units with multiplication, division or raising to a power.
(b) Often it is easier to work with the reciprocal of an expression.
Step 3: Always keep checking units to make sure you are working with the correct units.
Standardized Units U.S. and Metric
1. International Metric System Main system used around the world. Also known as
the SI (Système International d’Unités)
2. United States still also uses the U.S. Customary Systems (USCS) also sometimes called
the English System. (See Table 2.2 - 2.6)
Units of Density and Concentration
1. Density describes compactness or crowding; 2. Material density given in units of mass
per unit volume; i.e., g/cm3; 3. Population density given by the number of people per unit
area; 4. Information density how much information can be stored by digital media.
1. Concentration describes the amount of one substance mixed with another; 2. Concentration of an air pollutant measured by the number of molecules of the pollutant per million
molecules of air; 3. Blood alcohol content measured in units of grams of alcohol per 100
milliliters of blood.
Conversion Factors