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

["Frohne, Vickie" <VFrohne@BEN.EDU>]

Since the majority of the error in hand timing occurs when starting a=
nd stopping the timer, the better way to handle the pendulum is to st=
art the timer, count out 20 or more swings, then stop the timer. The =
stopwatch error is then reduced by a factor corresponding to the numb=
er of swings.  One might not want to do this for amplitude vs. period=
 (the amplitude changes too much over time). However, for m vs. T or =
 L vs. T timing multiple swings is far superior to timing one swing f=
ive times, and taking an average.
=20
The worst timing data is obtained by egalitarian students who divide =
up the work equally among team members.  One holds the watch, one say=
s "ready, set, go," one releases the whatever. It's usually better wh=
en one person does everything - cuts down on reaction time considerab=
ly.
=20
Vickie

________________________________

=46rom: Forum for Physics Educators on behalf of Rick Tarara
Sent: Mon 5/2/2005 10:14 AM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Reaction Time (was Re: Human Error?)



----- Original Message -----
=46rom: "Bernard Cleyet" <anngeorg@PACBELL.NET>


> "Someone will always offer--well you might not have started and sto=
pped
> the stopwatch precisely when the swing was at the MAXIMUM [bc's
> emphasis] of the swing."
>
> Since swing is written, I assume max. refers to max. displacement f=
rom
> the equilibrium position, not maximum speed, which is the point I
> thought EVERYONE was taught, whether by catechizing or just given, =
to
> use as the point to start and stop the timer.

Certainly not for timing a pendulum, especially hand timing.  The max=
imum
amplitude points are where the pendulum spends the most time--so the =
motion
is slower (although the acceleration is maximum) and it is easier to =
judge
the 'end points'.  Electronic timing might well use the equilibrium
position, but I would never have students use it for hand timing.

Rick
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