Re: Air resistance

[LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>]

SOME OF YOU MAY BE INTERESTED IN A MESSAGE AT THE END OF THIS POSTING.
IT WAS SENT TO MY PRIVATELY; IMPORTANT TO THOSE WHO USE MAC MOTION.

           On Mon, 15 Dec 1997 10:24:John Mallinckrodt asked:

> I hadn't previously understood that the d values *themselves* were 
> subject to smoothing.  Is that really true?  

I do not know; I am only a user of their product. Software unhanced
instuments can be tricky. For example, I can imagine the following
algorithm:

1) Was the absolute value of delta(dist) larger than 4 mm (one half
   of the wavelength) for any pair of cosecutive distances in the last 
   25 samples?

2) If the answer is NO then assume the object was not moving and
   display the average distance 25 times.

And a user looking at the table will think that measurements are
highly accurate.
                                                Ludwik Kowalski
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A PRIVATE MESSAGE FROM X:

.....  Logger Pro is a shipping product of Vernier's for Windows. The mac 
version is coming soon. Since LP uses the same algorithm for finding 
derivatives as MacMotion, the results should be the same. The difference 
is that you can separately control derivatives and averaging. 

Chicken wire, or just a wire secretary's in/out basket, can indeed be placed
over a motion detector to protect it from falling objects. The reflection
from the wire arrives _while_ the detector is emitting sound, so it's not a
problem.

The new case design for the Vernier motion detector (the one with the hinged
portion, rubber feet, and threaded clamp hole) seems to give slightly
quieter data. This is only a subjective feeling that I and others have about
the new case.
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