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MEASUREMENTS

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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 g – the 6 is estimated

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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

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Precise, Accurate, Neither, Both Precise and Accurate Neither Precise nor Accurate Precise

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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?

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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.

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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)

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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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