Re: [Phys-L] inertia and the tablecloth demo

[Anthony Lapinski <alapinski@pds.org>]

In my opinion, forces is the hardest topic for (high school) students. F =
ma is simple but not easy (to apply). That being said, the tablecloth demo
is a classic/effective demo for inertia. Yes, it can be analyzed further
(friction, impulse), but kids know about this demo. And everyone wants to
try it! There are many other 1st law demos where you want the object to
stay at rest (tennis ball hanger hat, bottle/hoop/marker, coin/card, two
bottles/wax paper, etc.).

Enjoy your new teaching adventure! Make it fun, interesting, relevant, and
engaging (FIRE)!

On Tue, Aug 16, 2016 at 11:18 PM, Richard Tarara <rtarara@saintmarys.edu>
wrote:

> The tablecloth demo as with many other commonly used demos is great for
> keeping the class awake but may well suffer (as you note) when it comes to
> conveying the physical principles you want to teach.  In my experience, the
> more simple the apparatus the better.  Then if you can't adequately explain
> the physics of the demo in less than 3 minutes, the lesson will not work
> for most (although the demo itself might be long remembered).  Everyone in
> my building knew when I was in class..something to do with the bowling ball
> that was almost always with me!
>
> rwt
>
>
> On 8/16/2016 10:52 PM, stefan jeglinski wrote:
>
> > For the first time this Fall, I'm teaching a class in "How Things Work"
> > to a group of non-science majors. This, I have never done before, and it's
> > a bit daunting to know that I need to connect to them in a different way
> > from STEM majors.
> >
> > At any rate, we're using the book How Things Work, by Bloomfield, and he
> > explains that the dishes remain on the table when you whisk a tablecloth
> > from under them "because of inertia." He expands only slightly, and I do
> > get what he's saying, but I feel like this isn't the best way to try to get
> > Newton's First Law across. This "experiment" depends sensitively on factors
> > such as the acceleration of the tablecloth, and the static and kinetic
> > coefficients of friction. If you use a looong tablecloth you will probably
> > get in trouble. To the contrary, it seems that friction is one of the
> > reasons that people don't really get the First Law: "objects in motion stay
> > in motion" but virtually everything that you slide across a table doesn't
> > do this. Isn't this regarded as one of the reasons that the
> > force-and-motion connection became so ingrained?
> >
> > Like I said, I do understand how one could use this demo to discuss the
> > first law, but it seems to me that a glider on an air track or a puck on an
> > air table are more instructive given a finite class time. What does
> > everyone think?
> >
> >
> >
> > Stefan Jeglinski
> >
> > _______________________________________________
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>
>
> --
> Richard Tarara
> Professor Emeritus
> Saint Mary's College
>
> free Physics educational software
> http://sites.saintmarys.edu/~rtarara/software.html
>
>
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