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Measurements

Measurements. Measurement. Measurements are uncertain for two reasons Instruments are never free of flaws Measuring involves some estimation When reading an instrument, the last digit is always estimated i.e. 1.256 g – the 6 is estimated. Precision and Accuracy . Precision

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Measurements

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  1. Measurements

  2. Measurement • Measurements are uncertain for two reasons • Instruments are never free of flaws • Measuring involves some estimation • When reading an instrument, the last digit is always estimated • i.e. 1.256 g – the 6 is estimated

  3. Precision and Accuracy • Precision • Repeated measurements that are close to each other • One measures the temp. of boiling water to be 85.0°C, 84.5°C, 84.7°C, and 84.9°C • Accuracy • Answer is close to an accepted value • Home Run

  4. Precise, Accurate, Neither, Both Precise and Accurate Precise Neither Precise nor Accurate

  5. Percent Error • Formula: |Accepted – Observed| Accepted * 100% • Molly tested the melting point of ice and found it to be 24°C. What is her percent error? • Susan only obtained 50 g of a sample. When she performed her calculations though, she calculated that she should have gotten 68 g. What is her percent error?

  6. Qualitative vs. Quantitative • Qualitative • Give results in a descriptive NON-NUMERIC form • i.e. The grass is green. • Quantitative • Give results in a descriptive NUMERIC form • There are 5 students in this class.

  7. Quantitative (QT) or Qualitative (QL) • The candle is cylindrical in shape. (QL) • The length decreased during the observation. (QL) • The candle is white. (QL) • The candle is 6 cm in length. (QT) • The flame flickers in response to the air. (QL)

  8. Observation vs. Interpretation • Observation • What you see • Interpretation • How you see it • Example: • A boy and a girl are walking down the hall • Observation • They are a couple. • Interpretation

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