Re: [Phys-l] unbiased experiments +- index of refraction

["LaMontagne, Bob" <RLAMONT@providence.edu>]

I hope there's more to "discovery labs" than this. I do an identical exercise with springs - one group studies the effect of mass on period, another studies the effect of amplitude, etc. The only difference between what I have described and what you have described is the point at which they encounter the equation for the period - at the begining of the exercise or at the end. I hope someone who has a strong definition of what a discovery lab actually is will chime in.

Bob at PC


________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Richard  Tarara [rbtarara@sprynet.com]
Sent: Tuesday, May 12, 2009 5:40 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] unbiased experiments +- index of refraction

----- Original Message -----
From: "John Denker" <jsd@av8n.com>
> That's the point:  the pendulum is so very far unbalanced in
> one direction that we can move a long ways in the other direction
> before we achieve balance, let alone start worrying about unbalance
> of the opposite kind.
Of course it depends how one structures a 'pendulum' lab.  In my classes, we
start with looking at a ball swinging on a string and decide that we should
take some measurements--perhaps this is a predictable, usable phenomena.
The students decide what should be measured, what should be varied, together
we work on a reasonably accurate way to time the motions, and then we go at
it.  I like to break this one into different groups doing different
aspects--one studying the mass of the bobs, one looking at the angle of
swing, three different groups looking at the length of the string--doing
different ranges which I have 'cleverly' chosen such that each group's
results will not be too inconsistent with a linear relationship but when
combines clear show something else (we can do a 10 meter pendulum in our
building) .  Each group reports their results.  After one lab they only come
to the conclusions that the period doesn't depend on the mass of the bob,
that the angle of swing matters, but not much below 30 degrees, and that the
length matters.  We return to the length data later to show that the
dependence is with the square-root of L.  We also get some help from a
fictional 'theoretical' group (an infinite number of monkeys with computers)
who have come up with a possible theoretical form that we can compare to our
empirical fits.  Since we have a constant and the monkeys have a constant
based on 'g', we can see if our constants are consistent--actually get an
experimental value for 'g' from our data--usually pretty close.  Then only
much later do we explain the angle dependence and the fact that the monkeys
used SHM to derive their formula when in fact, the pendulum is only
approximately SHM (swings less than 30 degrees).

Anyway, done like this, even the pendulum can be a long way in the 'other
direction'.  One does not have to be a 'true believer' to incorporate
aspects of inquiry into one's courses.  ;-)

Rick

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