Re: [Phys-l] Inertia?

[John Denker <jsd@av8n.com>]

On 11/11/2008 02:07 PM, Bernard Cleyet wrote:

> p.s. is JD appealing to authority?

Yes, I was.

Appeal to authority is _weak evidence_.  In the absence
of strong evidence, we rely on weak evidence.
   http://www.av8n.com/physics/authority.htm

If anybody has stronger evidence, please let us see it.

On 11/11/2008 01:29 PM, Joseph Bellina wrote:
> > I have a different problem with the word "inertia."  If you ask  
> > someone why a bowling ball rolls down the alley although no one is  
> > pushing it, they are liable to say "inertia," in the sense that it is  
> > the cause of the continued motion.  On those grounds alone I would  
> > argue for avoiding it.

Amen, brother!

IMHO, when the student asks "why the ball keeps going" 
that is the Wrong Question for multiple reasons.

First of all, one of the great turning points in the
history of science was when people realized that 
"keeping going" was the natural state of things, and
did not require further explanation.  In contrast,
if/when a thing slows down, we need to explain the
slowing down.

So, I emphatically agree that saying the ball keeps going
"because of inertia" is giving a name to something that
doesn't need a name.

For a beginning student, the answer stops there.  But
for a more advanced student, I would continue by saying
that "why" and "because" are tricky and misleading words
in this context.  The epoch, the real beginning of science 
as we know it, was when Galileo realized that it often 
suffices to explain _what happens_ ... and we don't
necessarily need to say how or why it happens.

Newton captured this in the famous expression "Hypotheses
non fingo".

For more about cause and effect, see
  http://www.av8n.com/physics/causation.htm