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Re: The air track experiment



Hi Jack,
I am intrigued by your post cuz I follow everything but your conclusion.
I agree that if the acceleration goes as t to the power b, then it follows
that v goes as t to the power (b+1) and x goes as t to the power (b+2).
From this it follows that x(v) goes as v to the power (b+2)/(b+1) = 1 +
1/(b+1).

So what? Where's the conundrum? I don't get the point!

_Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: JACK L. URETSKY (C)1998; HEP DIVISION, ARGONNE NATIONAL LAB ARGONNE,
IL 60439 <JLU@HEP.ANL.GOV>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, August 24, 1999 12:35 AM
Subject: The air track experiment


This experiment, as I have seen it, involves a sliding mass on
an
inclined air track. The mass is released from rest and slides a fixed
and
measured distance through a velocity measuring device. The distance
from
the point of release to the velocity measuring device is varied so that
one
measures the variation of distance traveled vs velocity. The
instructions
state the expected functional relationship between the two quanitities,
so
the student is invited to measure the (constant) value of the
acceleration and
, with some trig, the value of g. Truly, a mind-numbing exercise.
I suggest the following variation on this experiment. If the
acceleration
were a power, say a, of the time of travel, then the distance traveled
would
vary as a power 1 + 1/(a+1) of the final velocity of the mass. Now for
those
who would yell YOU'RE WRONG! to those who would propose that a is
different
from zero, I invite you to determine limits on a from a real experiment.
I
suggest, therefore, that instead of using this experiment to determine
the
constant g, the experiment be used to determine acceptable ranges of a.
I
think that I can guarantee that a=0 is not an assured outcome.
P.S. I once tried, in a lab, to duplicate the Galileo inclined
plane
experiments. All the inclined planes I could find were badly warped,
and the
results varied widely from the expected. It is my private opinion that
Galileo
"cooked" his results - go for it, inquisition! Well, Newton was caught
cooking
too, therby demonstrating the power of abstraction from uncertain
experimental
results.
Regards,
Jack

"These several facts prove nothing, for one cannot deduce a principle
from so
few examples, but they do at least indicate that the ability to learn to
spell
correctly is a gift; that it is born in a person, and that it is a sign
of
intellectual inferiority. By parity of reasoning, its absence is a sign
of
great mental power."
Mark Twain, "Extract from Eve's Diary'.