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Re: That jerk again!



At 17:28 11/18/97 -0800, you wrote:
It occurred to me while driving to the dentist that there is
a phenomenon I really don't understand. I decided that it
might involve jerk (no, not me). What do you guys think?

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. ...
Leigh

If the brake is applied when v = 0 precisely, there will
undoubtedly be some relative movement between (fixed) wheels
and body/chassis. (The force that motivates the backward
movement is still in effect and needs to be opposed.)
It is an objective of suspension design to ensure some
rearward compliance between these parts.
This will put a little hook in that linear velocity graph,
I suspect.

Sincerely,

brian whatcott <inet@intellisys.net>
Altus OK