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Re: transfer of momentum



I disagree. That argument makes sense to us, but not to non-science
majors who have never had physics in high school. The students seem to
understand a speed changing after a finite time. They don't grasp the
ratio of that speed change to the time interval. They feel that they
have an intuitive understanding of speed (they can 'see' motion). But
they have no intuitive sense of acceleration. Again, I think that's why
the momentum change approach to forces is preferable.

I would be willing to bet that if you took a biology or chem major who
has had a year of physics and asked them a couple of years after they
took the course 'If a ball is thrown upward at 40 m/s, what is its speed
after 2 seconds?', they will probably get it right. If you ask them the
acceleration at the peak of the ball's motion, I think most of them will
say 'zero'. (I bet most of the faculty would too!)

Bob at PC

"RAUBER, JOEL" wrote:



They need to explicitly consider a small but finite interval before and
after the maximum height (straddling the moment in time that the object is
at its apogee) and do all the stuff you say they can do above, and presto
they have derived that the acceleration at the top is g downwards.

Of course, they have to do it, not watch an instructor do it.