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[Phys-L] Re: A Third law question



On Thursday, October 13, 2005 5:30 PM, Hugh Haskell wrote (in part):

You are correct. One can start at either end of the chain and
arrive at the other. My argument is that momentum is
something that is more easily grasped, more visualizable as
it were and less abstract, than is acceleration, which is
inherent in Newton's laws.

I agree that momentum (which talks about changes) is more easily grasped
than acceleration (which is a RATE of change). On the other hand, you
don't need acceleration to learn about Newton's laws. For example, I
don't introduce acceleration until after learning about Newton's laws.
Until then, I talk about CHANGES in velocity. I do this to emphasize
the idea that WHILE the force is being applied the velocity CHANGES.
Once they understand this then I introduce the idea of RATE of change.

Perhaps your success is due more to the delay in introducing rates of
change (after changes) rather than the introduction of momentum first,
per se. Introducing momentum first is one way to do this but not the
only way.

P.S. When I do it this way, I find the students have a better grasp of
the N3L vs. N1L (based on my own FCI-like assessment) but it is still
far from where I would like it to be.

____________________________________________________
Robert Cohen, Chair, Department of Physics
East Stroudsburg University; E. Stroudsburg, PA 18301
570-422-3428; www.esu.edu/~bbq