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

[Anthony Lapinski <alapinski@pds.org>]

As I stated before, my students (regular and honors) find forces to be the
hardest topic. The third law is particularly challenging. A book rests on a
table. If the book's weight (true weight, mg) is the action force, then the
reaction force is the ___ on the ____ acting _____. Nobody gets this right!

On Fri, Aug 19, 2016 at 6:24 PM, Derek McKenzie <derek@physicsfootnotes.com>
wrote:

> Richard Tarara said:
>
> Actually I have always been baffled by the fact that many students DO
> NOT seem to know what you mean by push/pull or even up/down. In
> exercises to identify the 3rd law force pairs various situations, one
> (too) often gets a mish-mash of pushes for pulls, pulls for pushes, and
> often in the wrong directions. :-(
> -----------------------------------
>
> That surprises me actually. In any case, just to be clear, I am not a
> fan of identifying a force with a push/pull. As I argue in the following
> post:
>
> http://physicsfootnotes.com/force-does-not-cause-acceleration/
>
> it's best to keep cause/effect language out of it. Necessary even!
>
> Derek McKenzie
>
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