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The Metric System (SI)

The Metric System (SI). See http://online.cctt.org/physicslab/content/Phy1/lessonnotes/metricsystem/lessonSIsystem.asp. The Metric System (SI). See http://online.cctt.org/physicslab/content/Phy1/lessonnotes/metricsystem/lessonSIsystem.asp. Significant Figures (or Digits).

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The Metric System (SI)

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  1. The Metric System (SI) See http://online.cctt.org/physicslab/content/Phy1/lessonnotes/metricsystem/lessonSIsystem.asp

  2. The Metric System (SI) See http://online.cctt.org/physicslab/content/Phy1/lessonnotes/metricsystem/lessonSIsystem.asp

  3. Significant Figures (or Digits) a.k.a. Sig Figs or Sig Digs A figure or digit is significant if… it is a nonzero figure. (52 has 2 sig figs) it is a figure between nonzero figures. (502 has 3 sig figs) it is a zero to the right of a decimal point and following a nonzero figure. (52.00 has 4 sig figs) it is a zero to the right of a nonzero figure, but left of an understood decimal, ONLY if specifically indicated to be significant by a bar. (52000 has 3 sig figs) A figure or digit is NOT significant if… it is a placeholder zero. to the right of a decimal point and to the left of a nonzero figure, i.e., PLACEHOLDER (0.00052 has 2 sig figs) to the right of nonzero figures with an understood decimal, i.e., PLACEHOLDER (5200 has 2 sig figs)

  4. Rules for computations with significant figures… • Analogy: A chain is only as strong as its weakest link. Addition/Subtraction • Keep only the leftmost place of uncertain figures. It becomes the rightmost in the answer. (52.1 + 3.61972 = 55.7) Multiplication/Division • The number of significant figures in the answer cannot exceed the number of significant figures in the least precise factor. (52 x 0.0387564 = 2.0)

  5. Accuracy vs. Precision Target Analogy Precise, not accurate Accurate, not precise Both accurate & precise Neither accurate, nor precise

  6. Measuring Accuracy Accuracy is the closeness of measurements to an accepted value Absolute Error, Ea = |O-A| where O = observed value and A = accepted value Relative Error, Er = 100% (Ea / A)

  7. Measuring Precision Precision is the agreement among several measurements Absolute Deviation, Da = |O-M| where O = observed value and M = mean of measurements Relative Deviation, Dr = 100% (Daavg / M)

  8. Mass Density a measure of how much matter is packed in a given space Density = mass / volume On your own and before you get into your lab groups, come up with at least three questions about the accuracy and/or precision of density determination that your group could investigate.

  9. The table below gives the accepted value for the density of each material at standard temperature and pressure. What is the specific gravity of each one?

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