Re: kinematics, traditional or not

[Joe Heafner <heafnerj@VNET.NET>]

> From: Tim Folkerts <tfolkert@FHSU.EDU>
>
> I don't view kinematics as derived from dynamics, or as a special case of
> F=ma.
It *can* be the former, and it *is* the latter.

> The kinematic equations are merely mathematical definitions.  After
> DEFINING
> v==dr/dt and a==dv/dt , you can use calculus to DERIVE  x = 1/2at^2 +
> v(0)t+ x(0), etc for constant acceleration, or DERIVE a = v^2/r for
> circular motion.  This has nothing to do with forces.
What you say it true. However, students rarely recognize this no matter how hard we try to get the point across. They typically try to use these equations for cases where a is not constant.

> F = ma is a much deeper statement.  You can determine mass; you can
> determine acceleration; you can determine force.  It turns out that,
> EXPERIMENTALLY, F=ma.  There is nothing that a priori requires this
> particular relationship, it just happens that there is such a nice, simple
> relationship in the universe.  It is conceivable that an experiment might
> disagree with F=ma and that it would have to be modified.  But I don't see
> how you could change a==dv/dt==d^2r/dt^2.
It seems your words are true, but I don't understand the point.


Cheers,
Joe Heafner - Instructional Astronomy and Physics
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