Re: transfer of momentum

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

Rick wrote:

> Are you dealing with gen-ed students?  Yes, I do say 'if the velocity of the
> object changes' -- but how do they recognize if that is the case--by
> recognizing that the object has sped up, slowed down, or changed direction.
> So, the mantra is repeated often--does the object speed up, slow down, or
> change direction?  When looking at the Work Energy Theorem (you have a
> subtitle for this one, I know) where the Net Work = change in KE, again we
> look to whether the object has sped up or slowed down.   All of this is to
> stay within the realm of student's instinctual knowledge of motion--does it
> move, does it speed up, does it slow down, does it change direction--and
> then to try and develop a Newtonian view of all this.

I'm not sure I understand your objection to what I wrote and I wonder
if you are misinterpreting my point.  What I meant to distinguish
between was the concept of a derivative (i.e., a RATE of change, a
velocity that "IS changING") and the FAR simpler concept of a
quantity that has one value at one time and a different value at
another later time (i.e, a CHANGE, a velocity that "changES").

Students have an innate (and correct) idea that you do something to
an object and as a result its velocity changes.  We should use take
advantage of that fact.  All we have to do is make them understand
that the thing you "do" is provide an impulse.

It is far more difficult to get students to connect force properly
with acceleration because BOTH acceleration AND force are more
difficult concepts.

--
John Mallinckrodt        mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm