Re: Causation in Physics: F=ma

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

I think John has a much more rigorous definition of causation than most of
us would use in describing Newton's Second Law.

While I can fully agree that mass times acceleration does not cause or
define a force (it can measure a force or net force), I am not at all
uncomfortable with the notion that forces are necessary for an acceleration
and therefore, in my vocabulary, can be said to cause accelerations.

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
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----- Original Message -----
From: "John S. Denker" <jsd@AV8N.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, November 14, 2003 10:51 AM
Subject: Re: Causation in Physics: F=ma


> On 11/14/2003 10:20 AM, Justin Parke wrote:
> > Why do I so strongly want to believe that forces cause accelerations?
>
> A possibility:  Many people are constantly exposed to
> examples where they *calculate* the acceleration based
> on prior knowledge of the force, not vice versa.
>
> In such a case, it is correct to say we _know_ the
> mass*acceleration because we _know_ the force.
>
> But this does not prove that F causes ma, for multiple
> reasons:
>
>   1) Examples, even innumerable examples, do not prove
> the general case, especially when there are counterexamples.
> For instance, if I tell you the mass, radius, and
> rotation-rate of a centrifuge, you can calculate the
> acceleration and thence calculate the force.
>
>   2) As a point of fundamental logic, the cause of our
> *knowledge* of ma is not the cause of ma itself.
>
>   3) Cause should precede effect.  The force F does
> not precede the acceleration a=F/m ... they must
> both happen at the same time.
>
>   *) et cetera.
>
> For details see
>    http://www.av8n.com/physics/causation.htm