Measurement and Uncertainty

-no measurement is exact

-it's your best estimate

-if you count an object, it's the exact number. 

     ex. 10 pens stays as 10

Absolute Uncertainty

-uncertainty is expressed in the units of measurement not as a ratio

Method: 1- make at least 3 measurements. Get the average. Absolute uncertainty is the LARGEST difference between the average of lowest and highest of reasonable measurement

Ex.

                    Trial #                                            Mass of an object

                        1                                                         14.4g

                        2                                                         14.2g

                        3                                                         17.5g (remove)

                        4                                                         14.3g  

                        5                                                         14.1g

-Average: (of four reasonable measurements)

    =14.3g

-Difference between the average and low measurement:

    =14.3-14.1 = 0.2g

-Difference between high and average:

    =14.4-14.3 = 0.1g

Mass would be recorded as 14.3+0.2g

Method: 2- always measure to best precision as you can. So estimate to a fraction 0.1 of smallest segment on the instrument scale

ex. beaker: 25mL. Best precision is 2.5 mL

Relative Uncertainty & Significant Figures

Relative Uncertainty = Absolute Uncertainty

                                 estimated measurement

PRACTICE

Find the average, and the absolute uncertainty of these pictures