Re: Causation in Physics: F=ma

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

Robert Cohen wrote:

> ... the following is the thinking of the students:
>
> A force causes the object to have a velocity it didn't have before.
> This means that you apply a force and eventually the object has the new
> velocity.  It may take time, but eventually the object attains this new
> velocity.  It is this "new velocity" that is "caused" by the force.

and, as I have somewhat eccentrically maintained for many years, so
(pretty much) was the thinking of Newton.  I believe that Newton,
like our students, found the concept of acceleration at least a
little confusing.

Newton didn't think in terms of what we call forces and
accelerations; he thought in terms of what we call impulses and
changes in momentum.  His version of "Newton's second law" was that
the momentum of a body changes in proportion to the impulse applied
to it.  Since impulses DO (in some sense) "precede" (fully realized)
momentum changes, it is easier to think of them as "causing" those
momentum changes even if nothing is gained in doing so.

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