[Phys-L] Re: Energy & Projectile Lab

[Daniel Crowe <dcrowe@SOTC.ORG>]

The range would be 1.47 m if the marble did not rotate and did not lose
any mechanical energy.  The range would be 1.24 m if the marble rolls
without slipping but does not lose any mechanical energy.

A relative error of -24% from 1.47 m is 1.12 m, which has a relative error
of -10% from 1.24 m.  A range of 0.97 m has a relative error of -22% from
1.24 m.

I don't know the details of Dwight's apparatus, but my guess is that most
of the mechanical energy is lost when the marble collides with the table
at the bottom of the plastic tube.  The rest is probably due to air
resistance and the jostling of the marble as it descends the tube.

If you are not already using one, I recommend adding a transition with a
relatively large radius of curvature (probably several centimeters) to the
bottom of the tube to prevent a significantly-inelastic collision between
the marble and the table.

Daniel Crowe
Oklahoma School of Science and Mathematics
Ardmore Regional Center
dcrowe@sotc.org

On Thu, 17 Mar 2005 15:51:22 -0500, Dwight K. Souder <crvhs_dks@CRESTVIEW-
RICHLAND.K12.OH.US> wrote:

> Greetings everyone.  I'm looking for suggestions/advice for a lab.  We are
> currently going over potential/kinetic energy and recently covered
> projectiles.  I would like for them to do a lab that consists of both.
The
> idea I have (that I'm certain others had done) was to roll a marble down
> plastic tube.  The marble then would roll across and off of the lab table
> and hit the floor at a certain spot.  Based upon knowing how high the tube
> is from the table, they can calculate the speed of the marble as it exits
> the tube and rolls across the table.  Knowing the speed of the marble and
> height of the lab table, they should be able to figure the range of the
> marble.  To add some fun to it, I also planned on having them place
> bulls-eye of where they think it'll land...each ring was worth some
points.
> When I've tested the setup, I'm not getting very good results.  My setup
was
> the following:  top of the plastic tube was 60cm from the top of the lab
> table, 90.07cm from the lab table to the floor, and the marble's range was
> 97cm.  I figured that it should've landed 147cm from the edge of the lab
> table (about 34% error).  I've tried different tube heights and my error
> would fluctuate (the best being 24% error).
>
> I'm curious if others had done something similar and suggestions for
> improving my setup.
>
> Thank you,
> Dwight Souder
> Ashland, OH
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