Re: Favorite Test Questions

["Rick Tarara" <rbtarara@sprynet.com>]

Not sure what you actually come up with as the 'answer' to this, but  my
understanding (based on watching the sport and discussions on this list over
a year ago) are:

Tires are spun ONLY doing the burn in.  Spinning them in the actual race
results in an instant shut down and a loss.

The tires are spun TO MELT rubber from the tires and lay it down in the
region of the track where the car will start.

This is done BECAUSE the coefficient of friction is higher for rubber to
rubber than for rubber to asphalt.

Spinning the tires during the race is the 'kiss of death' because the
coefficient between rubber/liquid rubber/and asphalt is very low.  Again,
the tires are NOT spun during the actual race.

An associated question that I ask--if the force of friction is independent
of area (roughly so in this case) then why the wide tires?  Answer--so that
the tires DON'T melt during the actual race.  Frictional heating of the
tires is located over a larger object with lots of surface area to keep the
temperature from going above the melting point for the tire compound.

Rick
-----Original Message-----
From: Tim Folkerts <Tim.Folkerts@valpo.edu>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>
Date: Wednesday, March 11, 1998 11:16 AM
Subject: Favorite Test Questions


> On Tue, 10 Mar 1998 11:37:08 -0500 (EST) "Donald E. Simanek"
> <dsimanek@eagle.lhup.edu> wrote:
>
> > And if we, as teachers, give homework problems and exam questions which
> > can be "successfully" done by these methods, we will not encourage
> > physical thinking. We must exercise great ingenuity to structure our
> > measures of accomplishment so that all of these "crutches" are blocked
> > completely, so that a student simply cannot pass the course by using
them.
> So, who out there has some favorite questions (either for homework or
> for exams) that they would like to share?  Questions that make the
> students think rather than pick an equation from the text?
>
> Here's one that I tried that students really struggled with, testing
> understanding of friction.
>
>
>
> "To achieve maximum acceleration, drag racers spin their tires as they
> leave the starting line.  How does this compare with your understanding
> of static and kinetic friction?"
>
>
>
> Most of the students blindly go ahead spouting the party line, never
> realizing this example is exactly the opposite of what the model would
> suggest. And this is after we had discussed antilock breaks.  It takes a
> reasonably sharp student to recognize the dilemma, and an even  braver
> student to say that the text is wrong!
>
> Of course, now you have to grade an essay, rather that the math we are
> all comfortable with, but it would be good for us to see on paper what
> the students are _thinking_, not just the numbers and the equations
> they are _using_!
>
>
>
> ---   Tim Folkerts
>
>
> ********************************************************
> Timothy J. Folkerts               Tim.Folkerts@valpo.edu
> Dept. of Physics & Astronomy      219-464-6634
> Valparaiso University
> Valparaiso, IN  46383