I have very much enjoyed this exchange and I thank all those who have
weighed in. I agree with those who have complimented Rick's student.
She has the makings of a physicist. Given the curiosity, the training
in physics and in math is possible.
As a matter of pedagogy, I would suggest to Rick that she be given a
little time to think more about this. After all, many of the greatest
minds in history required more than 30 minutes to come around to
accepting N3.
I appreciate John's comments about momentum. I use a skateboard demo,
in which students push against a wall and against each other while on
skateboards (using spotters) to talk about N3. I agree that momentum is
at the heart of the issue, but I admit to using N3 to justify the
conservation of momentum in the first place. I have to think about this
now.
I also appreciate the discussion about deformation and how things push
back. I think that works when talking about a wall, but might be harder
for a student to grasp when talking about accelerating a disk, which
moves rather than deforms.
Nobody's ever challenged me on N3 the way Rick was challenged by this
student. Right now I would suggest saying something like, "Gee, I've
taken this for granted for so long that I have to think about what more
to say after saying that things push back when they're pushed. Maybe
you could think about it too and continue to experiment by accelerating
a massive object, like a container of laundry detergent, at different
rates and seeing what that feels like. To be continued..."
Thanks especially to Rick for sharing this with the group.