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

[Richard Tarara <rtarara@saintmarys.edu>]

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

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http://sites.saintmarys.edu/~rtarara/software.html