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Re: Systematic vs. Random



Students always blame experimental discrepancies on "systematic error,"
and often they are right. It is instructive, however, to make them
identify possible source of systematic error and determine the largest
effect that systematic error could plausibly have. After all,In a
"real" experiment, you would have to do this. Moreover, there is often
good physics hiding in discrepancies if the experiment was done
carefully. For instance, are they measuring L to the correct point on
the pendulum? This would be a "systematic error" that might reflect a
misunderstanding of the physics.

Tim Burgess wrote:

During a post lab discussion yesterday students were presenting
the results of the standard pendulum lab (l vs. T).

A student asserted that because the test plot of T^2 vs. l by another
team resulted in a y-intercept that was about 4% of the maximum T^2
value then there was probably a "systematic error". My first reaction
(while the students discussed this) was that this was not true. The bell
rang. All left. I will see them again last period today.

I would like to get the general thoughts some on this list might have
regarding the validity of making the "systematic error" assertion based on
y-intercept value (combined with 9 well fitted data points).

Thanks

Tim

--
Maurice Barnhill, mvb@udel.edu
http://www.physics.udel.edu/~barnhill/
Physics Dept., University of Delaware, Newark, DE 19716