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Insignificant figures

Page history last edited by Joe Redish 2 years, 8 months ago



The image from a iPhone GPS app shown at the right appeared on my facebook stream.


A. Given the accuracy in the position shown, how many of the digits after the decimal points do you trust in the first three position specifications (Latitude, Longitude, and Altitude)? Assume that the units of the Latitude and Longitude measurements are in degrees. Explain how you did your calculation. 


B. Assume that time measurements are perfectly accurate (not so, but this is probably a smaller effect than the position uncertainty), and that the velocity is calculated by the simple formula, <v> = Δxt. 


How big a time interval would the app need to use for you to be confident of the first digit after the decimal point in the velocity measurement?  


Explain why the uncertainty in the velocity that comes from the velocity in the position depends on the time interval used in calculating the velocity.


C. What distance specification does the last digit in the latitude (the last "5") compare to? Is it as big as a foot? A thumbnail? A human hair?


Joe Redish 7/16/17

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