Re: [Phys-l] F causes a

["Robert Cohen" <Robert.Cohen@po-box.esu.edu>]

Bob LaMontagne wrote:
> A ball bounces off a wall. What is the "cause" of that 
> bouncing motion? If the wall was absent, the ball would 
> continue its motion. But the force on the ball and the 
> acceleration of the ball occur simultaneously.

Food for thought:

Would it be appropriate to say the wall caused the force?  After all,
the wall would be there, with or without the force, but the force
wouldn't be there if there was no wall.  Furthermore, the wall has to be
there *prior* to the force being exerted (i.e., before the ball
arrives).  And, since F=ma, could we also say that the "wall caused the
acceleration of the ball"?

Could it be that "force causes acceleration" is short-hand for "object
causes force/acceleration"?

P.S. As I mentioned before, I don't believe it is pedagogically
advantageous to use the "F causes a" language until after students
clearly recognize what "F=ma" represents.  I haven't given much thought
to the above language (i.e., objects causing forces) and I'm not sure
that is pedagogically advantageous either, but I throw it out for
discussion nonetheless.

____________________________________________________
Robert Cohen, Chair, Department of Physics
East Stroudsburg University; E. Stroudsburg, PA 18301
570-422-3428; www.esu.edu/~bbq