Am I pushing your leg? (Was: CAUSATION IN PHYSICS)

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Sat, 14 Oct 2000, John Denker wrote:

> At 02:55 PM 10/14/00 -0500, John M. Clement wrote:
>
> > To accelerate a block you must push it.
>
> Not strictly true.
>   -- you might pull it instead of pushing it

I've always enjoyed doing the following demonstration which, I
think points to the generally artificial distinction between
"pushing" and "pulling":

Stand behind someone and "push" on her left shoulder with your
right hand and with your fingers extended toward her spine. Ask
her whether you are "pushing" or "pulling." Now, while maintaining
contact and exerting the same force on her shoulder, walk around
until you are facing her and ask again.

So what distinguishes a push from a pull?  Is it where the "agent"
is located?  That seems a little tortured in this case.  And even
if so, what *is* the agent here?  Or is it that "pushes cause
compression" and "pulls cause tension"?  I think any definition,
no matter how unambiguous, will fail the "common sense test" in
certain circumstances.  Fortunately, it is seldom if ever a useful
distinction anyway.

A force is a force, of course, of course.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm