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[Phys-L] Re: Reaction Time (was Re: Human Error?)



----- Original Message -----
From: "John Denker" <jsd@AV8N.COM>

On 05/02/05 12:12, Edmiston, Mike wrote in part:

Rick says the pendulum spends more time
at the ends of the swings and that makes it easier. I say that makes it
harder.

Yup.

I'm going to defend my choice to do the timing at the max amplitude points
from this point of view. If you watch the motion for a while, it is easier
to see the rhythm of the motion and therefore anticipate the time to start
and stop the timer. I understand that 'seeing' the exact point of maximum
swing is more difficult than seeing the exact point where the pendulum
passes through the equilibrium position, but I am not at all convinced that
the ability to trigger the stopwatch at the equilibrium point is as
reproducible. In the end though, it doesn't matter much--because as I
alluded to in the original post, the point here is to get the students to do
multiple swing timing (10-50), so the uncertainty in this measurement can be
reduced down to the precision of the timer.

And yes, I always do a sample 10 swing timing for the students, counting
1,2,----10. I read off my time, divide by 10 and announce I now have a
better measurement than my one swing timing. If I get no objects, then I
have to announce that NO, I've made almost a 10% error--what is it? Usually
then someone will figure out we only timed 9 full swings--and then the
instructions to always start the count at zero.

Rick
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