Re: Newton's 3rd Law

["Richard L. Bowman" <rbowman@bridgewater.edu>]

On Mon, 10 Jun 1996, James Mclean wrote:
> Tom K. McCarthy says:
>  > What's wrong with the notion of action/reaction?  By using concrete 
>  > examples to help the student experience Newton's 3rd Law, it seems quite 
>  > natural to describe these as action/reaction, ...
>
> I think that the problem is in the everyday usage of those words.
> If you are not using physics-speak, then you would probably say something
> like: 
>    action: I push the cart.
>    reaction: The cart moves.
> In terms of the 3rd law, the reaction should be that the cart pushes back
> on me.  You *could* teach that there are 2 meanings for the word reaction,
> the physics meaning and the everyday meaning.  But it's probably easier to
> avoid the confusing nomenclature altogether.

I agree with the idea of staying away from the "action-reaction"
terminology for another reason also.  Stating Newton's 3rd law as:
   "For every action there is an equal and opposite reation."
opens this law to be used to defend all kinds of social interactions, e.g.
I have heard it thrown around to defend why it is necessary to use "force"
to respond to insults spoken against us.  Whether that is a correct way to
respond or not, it definitely was not what Newton was trying to get at!

Richard
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Dr. Richard L. Bowman
Dept. of Physics                         e-mail:  rbowman@bridgewater.edu
Bridgewater College                                  phone:  540-828-5441
Bridgewater, VA  22812                                 FAX:  540-828-5479
  "http://www.bridgewater.edu/departments/physics/physics.html";
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