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[Phys-L] Re: Human Error?



This is where some good teaching using reformed pedagogy can be of value.
For example in Modeling the whole point of view is that the students are
creating a model for what they observe, and that this model can be modified
when necessary. The whole orientation is around what they observe rather
than what a book says. This point of view runs through virtually all of the
PER curricula, and should be a good antidote to the idea of accepted values
being used to calculate errors.

Unfortunately the idea of calculating experimental-accepted value is
actually promoted by some state curricula and is in many textbooks, and in
teacher's notes. If you want to fight this at its source then you have to
get involved in the state curriculum committees.

John M. Clement
Houston, TX



As an aside, I do have this same problem with juniors and seniors in my
experimental
physics course for physics majors at our university. They think that
their only
discussion in the lab report should be about "error" and often ignore the
physics of the
experiment. They do have this belief that there is always some "accepted
value" and
that there is no way they can make a measurement without "human error."
In one
recent report, a student claimed, "The error in this case cannot be human
error because
all of the data was measured using a computer."

The experiment in question is the Kater pendulum, where our objective is
to measure
the local value of the acceleration due to gravity to the fourth decimal
place. We get
this accuaracy by measuring over 125 periods at each of 32 bob positions;
and by
measuring the distance between the two fulcrums to within 100 microns
using a
precision cathetometer. Even though it is communicated to the students
that our goal is
a precise measurement of g, some of them still want to compare it with the
book value
of 9.81 m/s^2 and calculate a percent error, even though it is clearly
stated not to
compare the measured result with any other number. They are asked to do
an
uncertainty propagation to prove the precision of the measurement. Almost
none of the
students attempt this, even though they were given practice problems at
the beginning
of the semester on how to do it.
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