Re: That jerk again!

[George Spagna <gspagna@rmc.edu>]

At 05:28 PM 11/18/97 -0800, Leigh Palmer wrote:
> If my car is in neutral and I roll slowly up a slight grade I
> eventually reverse my direction and roll back down. The
> turnaround is very smooth; I feel no sudden discontinuity. I
> have tried to apply my brake at the instant of the turnaround
> many times in this situation, and whenever I do I feel a
> discontinuity in the motion. I'm convinced that I've hit the
> instant dead on more than once, but still the discontinuity
> is always present, and not noticeably varying in magnitude.
>
> What's happening here? There is no discontinuity in velocity,
> but when I apply the brake there is a discontinuity in the
> acceleration. Of course the car is in equilibrium in an
> accelerated frame while it slows, but I can't believe that is
> the cause (the rapid change to a nonaccelerating frame)
> because the acceleration can vary a great deal and the
> subjective discontinuity does not seem to do so.

Your ability to react is limited (say about .25 s), and the mechanical
response of the car is not instantaneous either.  I guess I would be
skiptical of your ability to "hit the instant dead on".

George Spagna           **********************************************
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