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2-2: Units of Measurement

2-2: Units of Measurement. Objectives: Name SI units for length, mass, time, volume, and density Distinguish between mass and weight Perform density calculations Transform a statement of equality to a conversion factor. SI Measurement. Le Systeme International d’Unites Abbreviated SI

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2-2: Units of Measurement

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  1. 2-2: Units of Measurement Objectives: Name SI units for length, mass, time, volume, and density Distinguish between mass and weight Perform density calculations Transform a statement of equality to a conversion factor

  2. SI Measurement • Le Systeme International d’Unites • Abbreviated SI • Adopted 1960 as world-wide agreed upon standards • Defined in terms of standards of measurements

  3. SI Base Units • There are 7 base units in SI

  4. Some SI Base Units • Mass • A measure of the amount of matter in an object • SI unit for mass is the kilogram (kg) • The gram (g) is more useful for measure masses of small objects • The milligram (mg) is used for even smaller objects • Length • SI standard unit for length is the meter (m) • The kilometer (km) is used to express longer distances • The centimeter (cm) is used to express shorter distances

  5. Metric Prefixes • Prefixes are added to the names of SI base units to represent quantities that are larger or smaller than the base units

  6. Derived SI Units • Derived units: combinations of SI base units • Produced by multiplying or dividing standard units • Examples: • Area m2 length x width • Volume m3 length x width x width • Density

  7. Volume • Volume: the amount of space occupied by an object • The derived SI unit is cubic meters (m3) • One cubic meter = the volume of a cube whose edges are 1 m long • Cubic centimeter (cm3) is usually used because m3 is a very large unit • Volumes of liquids and gases are often measured by a non-SI unit called the liter (L) • 1 L = 1000 cm3 • The milliliter (mL) is used for smaller volumes • 1000 mL = 1 L • 1000 mL = 1 L = 1000 cm3 1 mL = 1 cm3!

  8. Density • Density: the ratio of mass to volume, or mass divided by volume • The SI unit for density is •  Units are too large! • Unit often used is grams or • A characteristic physical property of a substance • Can be used as one property to help identify a substance

  9. m Helpful hint: D V m m V D V D

  10. Sample Problem • A sample of aluminum has a mass of 8.4 g. The volume of the sample is 3.1 cm3. Calculate the density of the aluminum. • Given: mass (m) = 8.4 g volume (V) = 3.1 cm3 • Unknown: density (D) • You know that • Plug in the values!

  11. You Try! • What is the density of a block of marble that occupied 310 cm3 and has a mass of 853 g? • 2.75 g/cm3 • Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of 0.350 cm3? • 1.14 g • What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is 13.6 g/mL? • 5.60 mL

  12. Conversion Factors • Conversion factor: a ratio from the equality between two different units that can be used to convert from one unit to the other • Example: • 1 dollar = 4 quarters or 4 quarters = 1 dollar • or • When you want to use a conversion factor to change a unit in a problem, you can set up the problem the following way: • Example: How many quarters are in 12 dollars?

  13. You can convert factors if you know the relationship between the unit you have and the unit you want! • Example: • deci- means “1/10” • 1 meter (m) = 10 decimeters (dm) AND • deci- also means “0.1” • 0.1 meter (m) = 1 decimeter (dm)  You can write the following conversion factors relating meters and decimeters

  14. Sample Problem • Express a mass of 5.712 grams in milligrams and in kilograms. • Given: 5.712 g • Unknown: mass in mg and kg • Solution: •  mg: The expression that relates grams to milligrams is 1 mg = 0.001 g • The possible conversion factors are •  kg: To find kilogram is similar 1 kg = 1000 g • The possible conversion factors are

  15. You Try! • Express a length of 16.45 m in centimeters and in kilometers. • Answers: • 1645 cm • 0.01645 km

  16. 1000 Stair Step Method 100 Kilo- 10 Hecto- Deka- 1 0.1 King Base Unit 0.01 Henry Deci- 0.001 Centi- Died By Milli- Drinking Base units: Mass = Gram (g) Length = Meter (m) Volume = Liter (L) Chocolate Milk

  17. You Try! • Express a mass of 0.014 mg in grams. • Answer: 0.000014 g

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