# PHY 125 – Error, Uncertainty & Tolerance

Published on: Wed Jan 27 2010

Location ← Say “Position” instead Si (System International) is also known as mks (meter, kilogram, second) Combination of Units You can combine the three base units to describe other things. Speed = miles per hour [English System] or meters per Second [Si] Conversion of Units 1 inch = 2.54cm 1 foot = 12 ● (inch) = 12 ● (2.54 cm) Significant Figures
▬Relates to the # of significant figures given in the input ▬Rule of thumb
Area = Width ● Height = W ● H If we say W = 1.00m, we mean 1.00m not 1.01m or .99m If W = 1.00m and L = 3.33m, the Area = 3.33m² What would happen in W = 1.01m and L = 3.33m? Then we are stuck with this slightly odd number 3.3633m², but since the input numbers contain only three significant numbers, we need to round the slightly odd number to 3.36m². What if W = 1.01m and L = 3.3m? Then we need to round the slightly odd number (3.333) to 3.3m². Because we are rounding to the LEAST significant number of digits in the given input. Error and Uncertainty Error is not as common of a term, and this concept refers to the tolerance, i.e.: Margin for Error. width = W = 1.000m ← accurate to millimeter = 1.000 ± .001m 1.000 ± .001m = width is in the range {1.001m , 0.999m} = W±∆W ±∆W = amount of variation in W W = measurement *****NOTE***** To Determine the uncertainty of a measurement, repeat the measurement to find the distribution curve. Adding & Subtracting Uncertainty Perimeter = P = 2L + 2W Perimeter with uncertainty P±∆P = 2(L±∆L) + 2(W±∆W) = 2L+2W ±2∆W ±2∆L Maximum Perimeter = P +2∆W + 2∆L Minimum Perimeter = P -2∆W - 2∆L