MEASUREMENTS Measurement Measurements are uncertain for two reasons

MEASUREMENTS

Measurement Ø Measurements are uncertain for two reasons Ø Instruments are never free of flaws Ø Measuring involves some estimation Ø When reading an instrument, the last digit is always estimated Ø i. e. 1. 256 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 Ø Qualitative Ø Give results in a descriptive NON-NUMERIC form Ø i. e. Ø The grass is green. Quantitative Ø Give results in a descriptive NUMERIC form Ø There are 5 students in this class.

Quantitative (QT) or Qualitative (QL) v v v 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 Interpretation � How you see it Example: �A boy and a girl are walking down the hall Observation � They are a couple. Interpretation