"Tom Anderson" wrote in message
h.li...
On Sat, 19 Jan 2008, asdf wrote:

On Sat, 19 Jan 2008 10:13:13 -0800 (PST), Mizter T wrote:

I'm getting on a bit (brings out violin) and my back doesn't like all
the excitement of the unplanned roller coaster ride the Victoria Line
can be.

Roll on the invention of inertial dampers :-)

Fair enough, I see your point - and yes, I suppose the Victoria line can
be a bit jerky. Perhaps the new stock on the upgraded line will manage
to do the job in a smoother manner, without sacrificing the speed.

That seems perfectly possible - they could lower the rate of change of
deceleration, without significantly sacrificing the magnitude of the
deceleration.

You beat me to it! The rate of change of acceleration [1] is known as
'jerk rate', and it's primarily that, rather than the magnitude of the
acceleration, which determines passenger comfort. Well, until the
acceleration is a significant fraction of gravity, but i don't think we're
likely to see that - normal braking is usually on the order of 1 m/s^2, i
think. You can indeed reduce the jerk rate while maintaining the same
deceleration; it means it'll take a little longer to come up to full
braking, but the extra time is negligible compared to the time then spent
at full brake. The jerk rate is entirely limited by the sophistication of
the control system, i believe; the primitive computers on the current
Victoria line trains probably don't make any attempt to control it, and
just switch between acceleration rates as quickly possible. I'd hope the
new stock makes more effort here.

tom

[1] The fourth derivative of position with respect to time - fourth!

Velocity is the first derivative, and acceleration is the second derivative.
What are you regarding as the third derivative if you are calling the rate
of change of acceleration the fourth derivative?
--
David Biddulph