Tom Anderson wrote:
On Tue, 3 Jan 2006, Brimstone wrote:

Tom Anderson wrote:
On Mon, 2 Jan 2006, Bob wrote:

Does anybody know if humps are still built into station tracks on
new tube lines.

The CTRL seems to do it:

http://www.ctrl.co.uk/route/tile1.asp?L=8

Although i don't know if that's really about playing tricks with
energy, or wanting to keep the tunnel nice and deep where possible.

When done by the CRL I don't think it was about "playing tricks with
energy". Electricity was still a very new form of energy and such
considerations hadn't arisen, it was simply a way of using a natural
phenomenon (gravity) to improve the performance of the trains.
However good the braking and acceleration of a vehicle on the level
it will be enhanced by going up/down hill at the appropriate moment.

Er, that *is* playing tricks with energy - the uphill slope of the
hump is a machine which converts the train's kinetic energy into
gravitational potential energy, thereby assisting the brakes, and the
downhill slope is a machine which does the inverse, delivering energy
into the acceleration process, and so assisting the motor.

It's exactly like using regenerative braking to turn a train's kinetic
energy into electrical energy during braking, which can then be
reconverted into kinetic energy during acceleration - only the hump
does it rather more reliably and efficiently!

A third equivalent would be a colossal spring lining the tunnel,
which the train would compress during braking, and whose expansion
would assist departure. Far less efficient (ISTR that you lose at
least half the energy to heat when you do that), and probably not the
most reliable or safe approach, either.

If you want to take "energy" in the widest sense, rather than the limited
term meaning that which powers the train OK.