🚀 go-pugleaf

We solved the problem buy subtracting out the momentum (mgt) due to
gravity while the Troll is under the influence of the cord.  I get very
good results where we use a glider on a horizontal air track.

You might try the new MPLI for Windows.  I think that program is superior
to Motion for DOS machines.

Lowell

Project PHYSLab
The Catlin Gabel School
Portland, OR 97225

On Wed, 7 Dec 1994, Brandon Kovach wrote:

> I have done exactly this lab in my classes this semester.  We used the
> aircart instead of a troll, but it was still irritating.  First thing I
> would check is to see how many times the computer is sampling the force
> sensor.  We used differen software (Motion Plotter) and it isn't fast
> enough to account for less than 10% error or so.  You should be able to
> see how many times it is sampled some how, if only counting the dots on
> the screen.
>       Second, it turns out that the mass of the bungee cord seems to be
> more relevant than one might think.  It can be calculated only to about
> 50% accuracy as I figure, but sometimes it helps to add that in to the
> theoretical value.  You might check this by comparing the mass of the
> string to the mass of the troll, if they are different by less than 90%,
> I would consider this a major source of error.
>       Try the sampling rate and the cord momentum and see what you get.
> Brandon Kovach
> Drury College
> Springfield, Mo
>
>
> On Sat, 3 Dec 1994, Lowell Herr wrote:
>
> > I am trying an impulse - change in momentum experiment with my students
> > and we are getting a 30% error.  Let me explain.
> > 1.  By sending a glider across an air track, a rubber bumper on the glider
> > collides and rebounds off a force probe.  Measuring the area under the
> > F*delta t graph (using MacMotion software) we can compare the impulse with
> > the change in momentum of the glider.  This works within a few %.  No
> > problems.
> >
> > 2.  Now we set up a Bungee Jumper using a Troll that is pushed off a
> > platform with a long rubber band attached to the Troll's ankle and a force
> > probe.  The velocity of the falling Troll is calculated just before the
> > rubber band begins to stretch.  Knowing the change in momentum of the
> > Troll during the fall and related rebound, one can calculate the change in
> > momentum.  In this experiment, the impulse comes out 30% higher than the
> > change in momentum.  I have gone through the experiment several times and
> > cannot account for such a large difference.  The impulse curve generated
> > is very symmetrical and consistent.  The Troll I am using has a mass of
> > 0.23 kg placing a good force on the probe as it falls 73 cm (using
> > center-of-mass measurements).  I have the probe locked down quite well so
> > as to reduce vibrations.  I have calibrated the probe several times
> > thinking that might be a problem.  Any suggestions?  The impulse is
> > consistently 30% - 35% higher than the change in momentum.
> >
> > Lowell Herr
> > Project PHYSLab
> > The Catlin Gabel School
> > Portland, OR 97225
> >