Re: Feeling Acceleration

["Richard W. Tarara" <rtarara@saintmarys.edu>]

I disagree with the first part of this paragraph quoted from Donald, but
agree fully with the second half.

It is exactly the human sensations with which we must begin if we are to
capture the attention and the interest of most students.  I don't think we
have to get into the nitty-gritty of the physiology (although I tend to do
such with sight and hearing) to deal with issues such as:  We feel 'heavy'
at the bottom of a Ferris wheel and 'light' at the top--WHY?  To answer, we
must first deal with the 'apparent weight' argument--that we experience our
weight through the forces (or pressures) that prevent gravitational
free-fall.  Now analyze the motion.  Circular motion requires a net force
towards the center so at the top the only downward force is that due to
gravity (no GR explanations here) which must be greater than the force of
the seat upwards.  Since the gravitational force doesn't change (over the
height of the wheel) then the force of the seat must be smaller than it
would be if we were at rest.  Now BECAUSE we experience weight backwards
(through the push of the seat) we feel lighter.  Likewise at the bottom,
the seat must push up with more force than the gravitational force, and
again experiencing forces backwards, we feel heavier.  I also like to deal
with the 3 and 9 O'clock positions (having a seat with NO cross bar!)

The above STARTS with student's perceptions of 'weight' in an accelerating
frame and uses simple Newtonian mechanics to analyze what is really going
on (in a Newtonian framework).  No need to super-analyze the physiological
processes--the students understand these sensations just fine.  	

A separate comment:

As always, these threads elicit a broad range on explanations which must be
sorted out for appropriateness for different audiences.  General Relativity
approaches to standard 'weight' and mechanics problems are more for 'our'
enlightenment than for student consumption.  I suspect the majority (and
maybe the vast majority) of people on this list are teaching at the HS and
Introductory College level and often these discussions get skewed toward
'graduate level' analyses.  The rest of us can learn much from these
essays, but must keep in mind that we will probably have to settle for a
'somewhat' simpler explanation in our classes.  Of course there's always
the DELETE key ;-) !

Rick

----------
> From: Donald E. Simanek <dsimanek@eagle.lhup.edu>
>
> I think we are asking for trouble when we teachers try to relate physical
> concepts to things people sense and feel--unless we are willing to turn
> your courses into physiology courses by carefully examining the
> biiological chain of events between the physical stimuli and the response
> processed by the brain. Of course the sensory feelings are a first step
> for students, and were a first step historically in the development of
> physics. But we must go beyond that first step to get to physics.