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Re: [Phys-l] possible projectile lab



Dwight,

I have students roll a ball down a ramp off a counter top to land in a
cup on the floor. They get one chance. There are many interesting
components to this lab. I have them model the lab in interactive physics
as a test of their calculations. They spend an inordinate amount of time
trying to get the inclined plane drawn in IP. This mirrors the research
on how novice students fail to see the important points as they focus on
the non-important elements. They see that in IP the ball can be given an
initial velocity without a ramp. The ramp was only a convenient way of
giving the ball a reproducible velocity.

Additionally, they are not at all clear on what velocity to use. We set
the photogate up at the edge of the counter since we do not care what
the velocity is at the end of the ramp, but what it is as it leaves the
counter. We also have a problem because the photogate gives an average
velocity instead of an instantaneous velocity. How to get the velocity
of the ball is always interesting because they want to measure the
diameter of the ball. This is not easily done and it is an incorrect
assumption. The ball may not pass with the diameter at the IR light
level of the photogate. The neat way of getting the distance traveled by
the ball is to plant the ball on a piece of paper and pass the photogate
over the ball. (This reinforces the idea of reference frame). The
distance marked on the piece of paper is the distance that the photogate
"saw" the ball move.

There is also the issue of "coupling" the counter top with the floor. We
use a plum line for that. Then you need to make sure that you are
perpendicular. We use perpendicular bisectors for that. Then there is
the issue of how big of a cup you can hit. This is a great application
of standard deviation.

Needless to say, this is a great lab and a great experience for the
students.

Joe

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Ken Fox
Sent: Wednesday, December 16, 2009 10:31 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] possible projectile lab

I have done this as a class project both as you describe and with a
PASCO
projectile launcher set at an angle. It works very well. You have
written
up a good enough lab right here.

Ken Fox

On Wed, Dec 16, 2009 at 8:44 AM, Souder Dwight <
souder.dwight@crestviewschools.net> wrote:

Soon, my physics students will be covering projectile motion. I've
been
thinking of doing a new lab, but wanted to see if someone else had
already
done it, and/or suggestions.

I'm thinking of having the students roll marbles down an incline, have
it
roll across the lab table a short distance, and mark where it lands on
the
ground (get an average of its landing distance).

From the information as to where it lands and the height of the lab
table,
the students would then calculate its initial horizontal velocity.

Then comes the challenging part. I'm thinking of giving the students
2-4
rings (about 2-3 inches in diameter) and they would have to place them
in
equal intervals of the marble's path, so that the marble passes
through each
ring.

Has anyone done a similar lab? Any suggestions? If someone has
already
done this, could someone email me their lab?

Thank you in advance,
Dwight


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Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l