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

[Marc Kossover <zeke_kossover@YAHOO.COM>]

--- "EdmistonMike" <edmistonLBLUFFTON.EDU wrote:

> I
> have seen students start a watch, settle back to
> count 50 pendulum
> swings, set the watch down, then scramble to pick up
> the watch and find
> the stop button when they suddenly realize they are
> at count 49.

Reminds me of a story. I was doing the centripetal
force activity where you spin a stopper in a
horizontal circle with a string that goes through a
tube to a hanging mass.
<http/sargentwelchom/product.asp?pnLWL32A_EA>
My colleagues said that this experiment worked well,
that it wasn't that that difficult to determine the
centripetal force formula from the data.

Several groups were getting pretty good data (the m
v^2/r was about 15% different than the force) but one
group of otherwise pretty good experimentalists was
getting lousy data.

Finally, I went over to watch them spin the stopper
and realized that the person timing couldn't count
reliably  to 50. She'd lose her place, jumping up or
down by 10, or simply foforgetting number or two.
Since the velocity's squared, these errors were
magnified in her work.

Once we switched to someone else, everything worked
much better.

Marc "Zeke" Kossover
The Jewish Community High School of the Bay

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