Date: Wed, 27 Aug 2003 15:29:23 -0700

Author: Tom Johnson

Subject: Re: overhead electroscopes

Post:

Jason,

Here is some information.. About a year and and a half ago I bought a OHP
Projection Electroscope Item # WL1971C it cost $120.00
Sargent-Welch,
P. O. Box 5229,
Buffalo Grove, IL 60089-5229
Phone: (800) 727-4368 Fax: (800) 676-2540


At 04:22 PM 8/27/2003 -0400, you wrote:
>Our chemistry demo guy has discovered that he can't find a supplier for
>the Project-o-scope, a no-batteries electroscope meant to be operated on
>the stage of the overhead projector.
>
>Anyone know who still carries these or similar?
>much obleeged,
>-jmsj
>
>____________________________________________________
>Jason St. John 617.353.2634 stjohn@bu.edu
>Boston University Physics Lecture Demonstrations
>590 Commonwealth Ave. Boston, MA 02215


Tom G. Johnson
Lecture Demonstrator
Department of Physics
Webster B-5/B-7
Washington State University
Pullman, WA 99164-2814
Phone: (509)
335-5097
e-mail: johnstm@mail.wsu.edu
HomePage: http://www.physics.wsu.edu/demos/default.htm
From gnper090@wviz.org Wed Aug 27 20:13:23 2003
From: "Dick Heckathorn"
To:
Subject: RE: Sliding into first base
Date: Wed, 27 Aug 2003 20:17:01 -0400
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Greetings,

I think there is another reason to dive for the ball. When you dive for
the ball, you have more time to arrive at the ball compared if you ran
and caught it at a higher level. Thus the best way to catch is
determined by being able to get to the ball. If I can get to it running
without diving, then I will run. If not I will dive hoping this
additional time will get me to it.

To me, I would look at the force vector of the ground acting on the foot
to propel one along. When we run the sum of the forces on the runner is
zero (assuming that one is running at constant speed).

How does the horizontal component vary from this when one alters the
force to dive for the base?

How does the air resistance vary as one changes position?

Dick

"Science is nothing more than learning how to communicate with nature in
such a manner that it will talk back."

Helping teachers who facilitate, motivating students who learn.
Dick Heckathorn 14665 Pawnee Trail Middleburg Hts, OH 44130
440-826-0834
Physics Teacher CVCA 4687 Wyoga Rd Cuyahoga Falls, OH 44224
330-929-0575 VM 120


-----Original Message-----
From: owner-tap-l@listproc.appstate.edu
[mailto:owner-tap-l@listproc.appstate.edu] On Behalf Of Jerry DiMarco
Sent: Wednesday, August 27, 2003 5:58 PM
To: tap-l@listproc.appstate.edu
Subject: Re: Sliding into first base

Arguments about this topic can go on all day. It is difficult to
persuade someone that sliding head first, feet first, or standing up is
better because objective testing is hard to do in this situation. While

this may be covered in one of the "science of sports" books, we may be
able
to cut to the quick by considering a similar situation where it is
necessary to run somewhere as quickly as possible - i.e. chasing down a
fly
ball.
I think we can all agree that experienced outfielders would
eventually learn the best way to catch a fly ball that is at the limit
of
their reach. You've probably done it yourself or seen it done - you
have
to dive for it. This is very similar to diving head first into a base.
If
there was an easier or faster way to get there and make the catch,
that's
how experienced players would be doing it. But there isn't, so that's
why
pros dive for the ball.
So why don't experienced players slide into first base? It goes
against tradition, it's inconvenient and there is more risk of injury.
A
foot first slide would be slower and counterproductive because your last

step is not a full running step. John's analysis of a head first slide
is
valid but incomplete:
1) You want to hit the dirt just as you touch the bag, so there is no
slowing from the impact.
2) Even though it takes time to fall forward, you are still running
right
up to the moment before you hit the dirt. So there is minimal loss of
forward speed.
3) So it comes down to the difference in length between your stretched
out
legs (~5' for me) and your stretched out body (~7.5' for me).
You would get there a little sooner with a head first slide, but not
many
people are willing to do it...


Jerry


At 02:12 PM 8/27/2003, you wrote:
>Howdy all,
>
>I got this from a former student of mine, and I was wondering if anyone
>had thoughts on the matter or could point me to a reference.
>
>Cheers - Matt Lowry
>
>=========
>
>Hi Mr. Lowry,
>
>I was your student in Physics in 2001. I was just writing cause I just
>got into a somewhat heated argument about whether it's faster for a
>baseball player to dive headfirst into first base or to run full speed
>through the base. My argument being simply that the time it takes for
>you to fall and the resistance of hitting the dirt (while minimal
>because you're diving at the base) will slow you down enough to make it
>a step slower. I was just wondering if you had any information about a
>study that has taken place, or if you have an opinion on the matter.
>
>Thank you,
>John Ronzani


<><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

Jerry DiMarco
Manager of Lecture Demonstrations and Instructional Labs
Montana State Univ., Physics Dept.

Bozeman, MT

Our Motto: "There's a demo in there somewhere."

From hubisz@mindspring.com Wed Aug 27 21:15:18 2003

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