You comment:
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I don't understand your demonstration of Newton's 3'd law. You write:
[paraphrased by Tom Koch -------------------
.... skip most of my explanation of the activity and go to the offending
sentence ...
The rules are that you can only hit (or avoid) the other person's hands (no
grabbing), and you may not move your feet. The trick (and the connection to
Newton's Third Law) is to decide when to provide a reaction force for the
other person's push and when not to provide a reaction force.
-------------------- end of paraphrase, and back to Jack Uretsky's comment]
But there IS a reaction force whenever there is contact, whether or not the
other person decides to provide resistance.
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*I respond:*
I see your point. If I cause, say, a person's hand to accelerate, then
there's been an interaction, which means the person has provided a reaction
force for my action force. In my statement above, it may seem that I was
carelessly ignoring the difference between interactions within a player's own
body (say, at the shoulder) where they may perceive themselves as "pushing",
and interactions between players (which must occur where their palms or
fingers touch). Let me try to avoid that, by expanding the offensive
sentence.
This activity should help students understand that to be pushed one must push
back. To avoid being pushed at all, one must avoid contact with the hands of
one's opponent. (Thus allowing no interaction.) A player can also limit the
magnitude of the opponent's push to some relatively small amount, simply by
deciding to limit the magnitude of his/her own "reaction" push. (I can't
push you very hard if you stand with your hands held up limply -- this is my
mother's strategy.)
I hope this is clearer. If not, I'll be back from vacation after a week to
try again. (And I apologize if this response is slow ... my excuse is that I
receive messages from the list in digest form.)
*On second thought, I bet you really DID understand the demo as originally
put forth, so I might respond:*
There's not necessarily any contact. That was parenthetically stated in the
original description of the activity.