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Scientific Measurement

Scientific Measurement. Chapter 3. 3-1 The Importance of Measurement. Qualitative vs Quantitative Measurement What color vs What mass? Scientific Notation Powers of Ten. 3-2 Uncertainty in Measurements. Accuracy, Precision and Error

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Scientific Measurement

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  1. Scientific Measurement Chapter 3

  2. 3-1 The Importance of Measurement • Qualitative vs Quantitative Measurement • What color vs What mass? • Scientific Notation • Powers of Ten

  3. 3-2 Uncertainty in Measurements • Accuracy, Precision and Error • Communicate the quality of Experimental Data and Calculations

  4. 3-2 Uncertainty in Measurements • Accuracy • How close to the accepted value is the measurement?

  5. 3-2 Uncertainty in Measurements • Precision • How are the Data Grouped? • Tight vs Loose

  6. 3-2 Uncertainty in Measurements • Error = Accepted value – Experimental value • % Error = Error x 100% Accepted value

  7. Practice Problem • Suppose you compare a wooden meter stick to a certified standard meter stick and get the following data:

  8. Practice Problem • Length of wooden meter stick = 1.009 m (oops) • What should the “accepted value” be?

  9. Practice Problem • That’s right! 1.000 m • Error = accepted – experimental = 1.000 – 1.009 = -0.009 m

  10. Practice Problem • % Error = Error x 100% Accepted = -0.009m  x 100% 1.000m = 0.9 %

  11. Significant Figures in Measurements • How well do you know your data? Is it - • 0.8m • 0.75m • 0.753m • 0.7529m

  12. Significant Figures • All four measurements could have come from the same object measured with increasingly precise equipment. • “Degree of Precision”

  13. Significant Figures • Significant Figures show all digits directly obtained in a measurement plus the first estimated digit.

  14. Significant Figures • The number of significant figures in measurements is governed by RULES See pages 56 & 57 … beware the lowly zero, it will confuse you.

  15. Significant Figures • Exact numbers: infinite sig figs • counting numbers 1 cookie, 2 cookies … • defined quantities 1 meter = 100 centimeters

  16. Significant Figures in Calculations • It’s a different game. • You can’t know a calculated result any more precisely than your least precise term. • “Weakest Link”

  17. Significant Figures in Calculations • Rules governing addition/subtraction are • DIFFERENT • from the rules governing multiplication/division. • See pages 58-61

  18. 3-3: Units • SI = International System of Units • see Table 3.1 page 63 • Base units vs derived units.

  19. Units • SI is related to the metric system. • We generally use the metric system and its prefixes. • See Table 3.2 page 64

  20. Units: Length • Meter • Derived units: • Area (squared) • Volume (cubed)

  21. Units: Volume • Space matter occupies • Unit cubes • V= lwh = s3 • 1 cm x 1cm x 1cm = 1cm3 = 1ml • 1 liter = 1,000 ml

  22. Units: Mass • Amount of matter in object • Unaffected by gravity • 1 ml water = 1 gram

  23. Units: Density • Relates mass of an object to its volume • Property of all matter • Density = mass = m • volume v

  24. Units: Temperature • SI: Kelvin scale (absolute) • unit = K (kelvin) • Metric: Celsius • unit = C (degree Celsius) • Pet peeve: There is no such thing as a “Degree Kelvin”

  25. Units: Temperature • Convert from K to C • C = K – 273 • Convert C to K • K = C + 273

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