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

[Bernard Cleyet <anngeorg@PACBELL.NET>]

John is correct only if the paths are equal. i.e. / e.g. the brain
signals to start stopwatch and release the ball; the paths, I strongly
believe, are usually equal.  However, they may not be if th experimenter
suffers from a neurological impediment either in the operation in the
brain or the paths, e.g. mono-lateral carpal tunnel syndrome.   In the
case of anticipation of the floor ball collision, I suppose it's not
"technically" reaction time.  However, human error is still involved.

Obviously, as suggested, greater accuracy is obtained by using a floor
switch and a timer start using the same signal that eletro-mechanically
releases the ball.

For an intro lab., I think it's more instructive to use the lower tech.
(our bodies are low tech.???) methods.  There's kinesthetic info. and
transparency.  Furthermore it's an opportunity to discuss error!  The
error discussion is rather more complex and requires high resolution
instruments to detect w/ the hi-tech. method.

bc, believer in kinesthetic method, and eschewer of black boxes.

John Mallinckrodt wrote:
> There have been a couple of posts suggesting that "reaction time" is
> a source of uncertainty in experiments involving timing.  Indeed,
> when we talk about sources of uncertainty in timing experiments,
> reaction time is usually the first thing my students point to.
>
> My response is always to engage in a little pantomime.  I pretend I
> am holding a ball in one hand and a stopwatch in the other.  I then
> drop the ball, feign a very surprised expression, and lunge to start
> the stopwatch.  As I continue to watch the ball fall I am "surprised"
> again when it hits the ground and lunge once more to stop the
> stopwatch as quickly as possible after that event.  The students
> usually get my point immediately and we all share a laugh.
>
> If reaction time is genuinely a source of error in such experiments
> then you need to go back to the drawing board and redesign the
> experiment.  Reaction time can only affect such measurements if, for
> instance, a) you let your partner drop the ball while you run the
> stopwatch AND you insist that your partner give you no warning or b)
> you consciously refuse to watch the ball as it drops and wait for the
> sound of the ball hitting the floor before stopping the watch.
>
> Of course there will be variations in the times obtained from
> successive tme trials, but I maintain that they have essentially
> nothing to do with the phenomenon that is properly called "reaction
> time."
>
> John Mallinckrodt
> Cal Poly Pomona
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