Measurement and Uncertainty

Measurement and Uncertainty
-No measurement is exact.
-Only count a set of object can get an exact number.


Absolute Uncertainty
Method1: 

• make at least three measurement
• calculate the average
• the absolute uncertainty is the largest difference between average and lowest or highest reasonable measurement

Example:

trial#               Mass of object(g)

1                               20.5

2                               20.6

3                               20.3

4                               19.5 (remove)

5                               20.7

(20.5+20.6+20.3+20.7)/4=20.5g

Average:12.5

Difference between average and lowest:20.7-20.5=0.2g

Difference between average and highest:20.5-20.3=0.2g

The mass would be recorded as 20.5±0.2g

Method2: Determine the uncertainty of each instrument
Always make the best precision that you can,estimate to a fraction 0.1 of the smallest segment on the instrument scale.

Relative uncertainty=absolute uncertainty/estimated measurement
can be expressed in

• percentage
• significant figures