Re: [Phys-l] F causes a

[John Mallinckrodt <ajm@csupomona.edu>]

On May 14, 2006, at 10:40 AM, Michael Monce wrote:

>   How about these statements:
>
> 1) "an object has an acceleration which causes the net force acting  
> on it"
>
> 2) "an object has a net force acting on it which causes an  
> acceleration."
>
> Which one does everyone prefer?

I prefer the second.  Indeed, it is at least similar to the type of  
language that I regularly use, although I think I am more apt to say  
things like "the net force on the object causes it to accelerate" or  
"the object accelerates due to the net force acting on it."   
Moreover, I like to write the second law as a = F/m when teaching  
because I think it is easier for students to make sense of.

Nonetheless, I see absolutely no reason to *teach* that forces  
"cause" acceleration.  I don't perceive *any* advantage to doing so  
and I think it has several serious disadvantages not the least of  
which is that it  is devoid of physical meaning.  I want students to  
understand that physics is about determining and making use of  
relationships between measurable physical quantities, that it is not  
about distinguishing "cause" from "effect."  I want them to  
appreciate that they may just as readily determine forces from  
accelerations as vice versa.

John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>