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Chapter 2-2 Units of Measurement

Chapter 2-2 Units of Measurement. Modification of Mrs. Rugh’s presentation 9/22/14. Measurements. Measurements are information that represent quantities. Measurement is different from Quantity. Measurements. A quantity is something that has size, magnitude, or amount.

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Chapter 2-2 Units of Measurement

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  1. Chapter 2-2Units of Measurement Modification of Mrs. Rugh’s presentation 9/22/14

  2. Measurements • Measurements are information that represent quantities. • Measurement is different from Quantity

  3. Measurements • A quantity is something that has size, magnitude, or amount. • Example: 1 teaspoon Unit of measurement Measurement Quantity is volume

  4. Measurement Standards Le Systeme International d’Unites (SI) • Adopted in 1960 by the General Conference on Weights and Measures. • Now used and agreed upon by scientists around the world. • This is basically what we call the “metric” system

  5. SI system • Has 7 “base units” • Most other units are derived from combinations of 2 or more “base units” • Not all units in this book are SI units

  6. Measurement Standards • SI Units are defined in terms of standards of measurements. • In 1795 the meter was defined as one ten-millionth of the distance from the Earth's equator to the North Pole (at sea level) • Before 1927 the official meter was defined by the length of a platinum-iridium bar kept in France. • Since 1983, the meter has been defined as "the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second."[2]

  7. Measurement Standards • Kilogram is the base unit of mass and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK). • It is the only SI unit that is still defined by an artifact instead of a physical property. • However, there is discussion to define the kilogram in terms of a fundamental constant of nature.

  8. Measurement Standards • The second is the base unit of time • Since 1967, the second has been defined to be: • the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.[

  9. SI Base Units Quantity Unit Unit Quantity symbol name abbreviation Length lmeter m Mass m gram g Time t second s Temperature Tkelvin K Amount of nmole mol substance You have a handout with this information on it…

  10. Mass ≠ Weight • Mass is a measure of the amount of matter, weight depends on the local gravitational field. • We usually measure mass with a balance, weight is usually measured with a spring scale. • We will talk about MASS only in this class (leave weight for physics…

  11. Prefixes –what do they MEAN • The handout has the important prefixes you need to know on it. • You should know the prefixes on the handout because you will use them…over and over…and over again.

  12. Prefixes –what do they MEAN • Come up with one example of what you might measure with each of these units in meters.

  13. Which unit (with appropriate prefix) would you use to measure this stuff? • Diameter of an atom • Weight of an elephant • Area of the Tacoma Dome • Temperature of the summit of Mt. Rainier • Temperature in outer space

  14. Derived SI Units • Derive v. • Mathematics: Obtain (a function or equation) from another by a sequence of logical steps, for example by differentiation: the volume fraction of the soil can then be derived as a function of L Oxforddictionary.com

  15. Derived SI Units • derived units…units that are created by combining 2 or more SI Base Units (usually through multiplying or dividing base units). • For example: • Length (m) x Length (m) = Area (m2) • Mass (kg)/Volume (m3) = Density (kg/m3)

  16. Example: Volume • The amount of space occupied by an object. • Solids: m x m x m = m3 • Liquids and gases: 1 Liter = 1 dm3 = 1000 cm3 So 1 mL = 1 cm3

  17. Density • The ratio of mass to volume, or mass divided by volume • D = mass/volume or D = m/v • Often (though not always) expressed in units of g/cm3.

  18. Quick Check

  19. Now Do the Practice Problems Due tomorrow if you don’t finish in class…

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