Re: transfer of momentum

["RAUBER, JOEL" <JOEL_RAUBER@SDSTATE.EDU>]

> -----Original Message-----
> From: Bob LaMontagne [mailto:rlamont@POSTOFFICE.PROVIDENCE.EDU]
> Sent: Wednesday, November 19, 2003 10:55 AM
> To: PHYS-L@lists.nau.edu
> Subject: Re: transfer of momentum
>
> I find this to be the case with my non-science majors. They never fully
> understand the concept of 'acceleration'. But they can easily grasp the
> idea that when an object falls, it picks up 10 m/s in speed every
> second. They can work out fairly sophisticated problems just by making
> out a little table with the speed being 0 initially, 10 m/s after 1 sec,
> 20 m/s after 2 sec, etc. It also doesn't bother them in the least to
> think of the speed decreasing by 10 m/s every second as a ball rises.
> The transition from positive to negative speeds at the top never bothers
> them - in fact they usually suggest it before I do. But - mention
> acceleration and they're totally confused - especially the idea that the
> acceleration is g at the peak of the balls motion. They need to deal
> with finite intervals. I think this is one of the advantages of the
> momentum approach to N2.
>
> Bob at PC

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.