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Measurement and the Metric Syste m

Measurement and the Metric Syste m. Confusion in America. Do you buy milk in gallons or liters? Soda? Why? Why do high school athletes run track and field events in meters but a football field is in yards? Which unit of measure do you find at the deli counter?. The Metric System.

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Measurement and the Metric Syste m

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  1. Measurement and the Metric System

  2. Confusion in America • Do you buy milk in gallons or liters? Soda? Why? • Why do high school athletes run track and field events in meters but a football field is in yards? • Which unit of measure do you find at the deli counter?

  3. The Metric System • France, 1795 • Needed to reproduce data in experiments • The revised version of the metric system • SystemeInternationale d Unites (1960) • Units of 10 • Consists of base unit • Measurements consist of a quantity and a unit.

  4. Base Units – based on objects or physical events Frequency of microwave radiation from Cs-133 Distance light travels in a vacuum in 1/ 299,792,458 of a second.

  5. Typical Types of Measurement Length – distance between two points Mass – amount of matter in an object • Weight vs. Mass • Gravitational pull on an object Volume – amount of space in an object occupies • V = L x W x H – linear measure, solids • Liter is the measurement of a liquid or gas • Affected by temperature • Usually a direct relationship between temperature and volume, exception is water

  6. Typical Types of Measurement - cont Temperature – the measure of the average kinetic energy of a system 3 Scales • Fahrenheit, Celsius, Kelvin F = 1.8C + 32 K = 273 + C

  7. Practice Problems • Water boils at 100 C. What are the Fahrenheit and Kelvin temperatures? • The average human body temperature is around 98.6 F. What are the temperatures in Celsius and Kelvin?

  8. 3. Convert each temperature to Kelvin. • 54 °Celsius b. – 15° Fahrenheit • 4. Convert each temperature to degrees Fahrenheit. • a. 200 Kelvin b. 18° Celsius • 5. Convert each temperature to degrees Celsius. • a. 450 Kelvin b. 232° Fahrenheit

  9. 5,000 Mm is 5,000 megameters 4.5 µg is 4.5 micrograms

  10. Converting Metric Units – use conversion factors • How many Mm are in 1.2 km? • How many mL are in a 4.2 cL? • A day consists of 86,400 seconds. How many ms is that?

  11. Density - ratio of mass to volume in an object • Depends on the composition of the substance not the amount (intensive property) • Affected by temperature • Usually an indirect relationship between temperature and density, exception is water

  12. Density Problems

  13. More Problems

  14. Dimension Analysis • Always focus on the units, they will tell you what to do • Conversion factor is a ratio of equivalent values used to express the same quantity in different units. Always equal to 1. Examples: 1 foot = 12 inches, 3.785 L = 1 gallon

  15. Practice Problems A pool contains 225,000 gallons of water. How many mL of water is this? Mount Everest is 8847 meters high. How many feet is this? How many days are you in English class? Assume you go to every class for 180 days.

  16. Accuracy and Precision Accuracy – how close a measurement is to the actual value Precision – how close a series of measurements are to one another

  17. Accepted Denisty of Sucrose – 1.59g/cm3 Which student was the most accurate? Which student was the most precise?

  18. Percent Error • Quantifies the accuracy of an experiment • Ignore the +/- signs use the absolute value

  19. What is the percent error for each student if1.59 g/cm3 is the accepted density.

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