Re: [Phys-l] the importance of F causing ma (and not vice versa)

[trappe@physics.utexas.edu]

For me, it is important to state the situation as:  The "F" causes the  
"m" to "a", rather than that the F causes ma.  Assuming that an "a" is  
recognized to either mean changing from one velocity (motion) to  
another velocity (different motion), or its special case when one of  
those velocities is zero (starting or stoping motion, means that I  
might want to know how to "get things moving" or to "get things to  
stop moving/slow down".

I think that is a practical, useful application for almost anyone,  
regardless of what their future activity dictates.

I don't see the utility in F causes ma because I view the m as a  
property of the object, not the result of the F.  The "a", I view as a  
result of the F.  That F is very specifically acting on the m to which  
I apply it. The a I am seeking is the result, and is the a of the  
same, specific m.

Assuming I want to move something, I need to understand how to  
accomplish that movement with the most desireable results, for my  
specific view of what I want to happen.  The penalty I pay for not  
knowing is that I won't "get it right (read the easiest solution to my  
movement problem) except by chance.

With "Force equals ma", I get the whole combination, without the  
insight of what gets what to do what, eg, why don't I just assmue that  
Force causes the acceleration to have a mass? Again, my big concern  
lies in "subscripts" on the F, m, and a.  That is, they are all on the  
same object.  That is *NOT* obvious to most students, including many  
students after leaving the courses we teach.
..just one of the devil's...Karl


Quoting John Denker <jsd@av8n.com>:

> Rick Tarara wrote:
>
> > That forces _cause_ accelerations then is a pretty important concept
>
> OK, I'll bite.
>
> Let's forget everything else and discuss this one point, namely the
> _importance_ of "knowing" that forces cause accelerations (and not
> vice versa).
>
> Suppose I'm a student in your class.  Please motivate me.  Please tell
> me why I need to "know" that forces cause accelerations.
>
> In particular, suppose I plan on having a research career, calculating
> forces, measuring forces, calculating accelerations, measuring accelerations,
> et cetera, all day every day.
>
> What penalty will I pay for not "knowing" that forces cause accelerations?
>
> The question is addressed to everyone, not just Professor T:  What will I
> be able to do with "force causes ma" that I can't do with "force equals ma"?
>
>
> ===================
>
> I will not accept the answer that I need to "know" forces cause accelerations
> (and not vice versa) so that I can get a teaching job, teaching that "fact"
> to the next generation of students.  That argument is circular in the worst
> sense of the term.  I'm sorry to be hard-nosed about this, but I really want
> to see some objective scientific evidence.
>
> Also please don't tell me I need to "know" it in order to pass the class.  I
> am not well motivated by grades (and have the grades to prove it :-).  I want
> to know why this is important in the real world.
>
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