Measurement Error Summation
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Propagation Of Error Division
ads with us Physics Questions Tags Users Badges Unanswered Ask Question _ Physics Stack Exchange is error propagation formula physics a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute: Sign up Here's how error propagation square root it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top How to combine measurement error with statistic error up vote 10 down vote favorite 4 We have to measure
Error Propagation Average
a period of an oscillation. We are to take the time it takes for 50 oscillations multiple times. I know that I will have a $\Delta t = 0.1 \, \mathrm s$ because of my reaction time. If I now measure, say 40, 41 and 39 seconds in three runs, I will also have standard deviation of 1. What is the total error then? Do I add them up, like so? $$\sqrt{1^2 + 0.1^2}$$ Or is it just the 1 and
Combination Of Errors In Measurement
I discard the (systematic?) error of my reaction time? I wonder if I measure a huge number of times, the standard deviation should become tiny compared to my reaction time. Is the lower bound 0 or is it my reaction time with 0.1? measurement statistics error-analysis share|cite|improve this question edited Apr 9 '12 at 16:17 Qmechanic♦ 64.3k991242 asked Apr 9 '12 at 12:41 Martin Ueding 3,33221439 add a comment| 3 Answers 3 active oldest votes up vote 6 down vote accepted I think you're exercising an incorrect picture of statistics here - mixing the inputs and outputs. You are recording the result of a measurement, and the spread of these measurement values (we'll say they're normally distributed) is theoretically a consequence of all of the variation from all different sources. That is, every time you do it, the length of the string might be a little different, the air temperature might be a little different. Of course, all of these are fairly small and I'm just listing them for the sake of argument. The point is that the ultimate standard deviation of the measured value $\sigma$ should be the result of all individual sources (we will index by $i$), under the assumption that all sources of variation are also normally distributed. $$\sigma^2 = \sum_i^N{\sigma_i^2}$$ When we account for individual sources of variation in an experiment, we exercise some model that formalizes our expectation about the consistency of the experimen
or more quantities, each with their individual uncertainties, and then combine the information from these quantities in order to come up with a final result of our experiment. How can you state your answer for the combined result of these error propagation chemistry measurements and their uncertainties scientifically? The answer to this fairly common question depends on
Adding Errors In Quadrature
how the individual measurements are combined in the result. We will treat each case separately: Addition of measured quantities If you have error propagation calculator measured values for the quantities X, Y, and Z, with uncertainties dX, dY, and dZ, and your final result, R, is the sum or difference of these quantities, then the uncertainty dR is: Here http://physics.stackexchange.com/questions/23441/how-to-combine-measurement-error-with-statistic-error the upper equation is an approximation that can also serve as an upper bound for the error. Please note that the rule is the same for addition and subtraction of quantities. Example: Suppose we have measured the starting position as x1 = 9.3+-0.2 m and the finishing position as x2 = 14.4+-0.3 m. Then the displacement is: Dx = x2-x1 = 14.4 m - 9.3 m = 5.1 m and the http://lectureonline.cl.msu.edu/~mmp/labs/error/e2.htm error in the displacement is: (0.22 + 0.32)1/2 m = 0.36 m Multiplication of measured quantities In the same way as for sums and differences, we can also state the result for the case of multiplication and division: Again the upper line is an approximation and the lower line is the exact result for independent random uncertainties in the individual variables. And again please note that for the purpose of error calculation there is no difference between multiplication and division. Example: We have measured a displacement of x = 5.1+-0.4 m during a time of t = 0.4+-0.1 s. What is the average velocity and the error in the average velocity? v = x / t = 5.1 m / 0.4 s = 12.75 m/s and the uncertainty in the velocity is: dv = |v| [ (dx/x)2 + (dt/t)2 ]1/2 = 12.75 m/s [(0.4/5.1)2 + (0.1/0.4)2]1/2 = 3.34 m/s Multiplication with a constant What if you have measured the uncertainty in an observable X, and you need to multiply it with a constant that is known exactly? What is the error then? This is easy: just multiply the error in X with the absolute value of the constant, and this will give you the error in R: If you comp
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