Re: That jerk again!

[flemmerhirt@mail.wcc.cc.il.us (Fred Lemmerhirt)]

> Nope.  There *is* a difference.  The difference is the very large jerk
>
> (time derivative of the acceleration) which *is* felt and causes
> distinct
> discomfort.

How is jerk "felt"?  Is there a "feelable" quantity like force (but
distinct from it) that is proportional to the jerk (da/dt) in the same
way that force is proportional to acceleration (dv/dt)?  (Of course, if
it happens slowly enough, I can just feel the force changing.  If I
brake progressively harder in bringing my car to rest, I feel the force
from my shoulder belt increasing and  attribute this change to the
jerk.)

The explanations of the "Palmer Phenomenon" that I've been reading seem
to indicate that the body of the car continues its backward
acceleration, acquiring a slight backward velocity before the suspension
"catches" it; and that there is then a forward acceleration as it
abruptly comes to rest (and maybe even recoils forward a bit).  Am I
interpreting this correctly?  How do we distinguish the force
accompanying this acceleration from some sensation resulting from
"jerk"?  I can't remember if Leigh specified the direction of the
sensation experienced in this situation.