Re: momentum before force (was: friction)

["Paul Camp" <pjcamp@coastal.edu>]

> Raacc@aol.com says:
> > ...
> > It seems to me that velocity should be introduced followed immediately by
> > momentum.  Then acceleration and net force can be defined as the slopes of
> > the velocity and momentum graphs respectively.)
> > ...
>
> When you teach this sequence, how do you justify momentum before force has
> been introduced?  Using a qualitative idea of force?

> --James McLean

Isn't this the way Newton did it? Not to say that it is necessarily 
the most transparent way but I believe Newton first wrote the second 
law in terms of rate of change of momentum rather than acceleration.

The idea goes back at least to the middle ages when Philoponus wrote 
(in Commentary on Aristotle's Physics) "it is necessary to assume 
that some incorporeal motive force is imparted by the projector to 
the projectile. . ." an idea which later gained the name of impetus 
and more or less corresponds to the modern notion of momentum. So 
the idea of momentum has a pretty long pedigree predating the 
Newtonian relationship with force.

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