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The Natural Philosopher[_2_]

Terry Casey wrote:
In article , lid says...
dennis@home wrote:

Extra mass doesn't help when going up and down hills unless you think
doing 1 mph on the level and rolling down a hill up to 70(or whatever
the speed limit is) and then slowing down to 1 mph as you go up the
other side is actually useful. Driving at the speed limit means there is
nowhere to store any extra kinetic energy without speeding up which is
probably both illegal and dangerous.
Some tube train lines use this principle by having tubes that go down
between stations.

But its an expensive way to save electricity.

A bit of oversimplification there! Which would mean that long tube lines
would end up with a vast disparity in tunnel depth at the ends!

In practice, the method used is to build the stations on 'hills' in the
tunnel network with a sharp incline on the approach to assist fast
stopping and a longer, shallower gradient beyond the station to aid
rapid acceleration on departure.

I don't see how this is any more expensive than boring tunnels without
the gradients ...

doesn't work well in the reverse direction ..if it ain't symmetrical.