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 g – the 6 is estimated

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

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

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?

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.

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)

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