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Re: Internal or external?

Ludwik wrote
Should we also insist on the "earth
acting on the rock with the force W"? Would the "F acting
on Q" irritate you?

What I would much rather have students say and write and think is "W
is the force exerted by the earth on the rock"
See, for example, Lillian McDermott's Tutorials in Introductory
Physics.


Would you object to the "effect of that
potential on the trajectory of Q"?

Yes, I think so. It's surely forces that affect the trajectory
(Newton's second law).


In my opinion harmless shortcuts are useful.

Ah, yes, but how do we know whether or not the shortcut is harmless or
whether it supports or even generates misconceptions? (Answer: by
examining the results of physics education research.)

Brian McInnes