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# GraviTrain

Gravity-driven slow, super-efficient train
 (+5, -2) [vote for, against]

Imagine two cities, Abilene and Beauford, between which freight has to be hauled on a regular basis.

Both of these fair cities have GraviTrain stations, each consisting of a raised departure platform and a ground-level arrival platform, and a huge hydraulic elevator.

The departure platform of Abilene is linked to the arrival platform of Beauford via a slightly inclined railway (and vice versa). Once the cargo (e.g., powdered mashed potatoes) is loaded, the railcars are raised from the arrival platform to the departure platform and let loose to roll gently down to their destination.

As the train glides slowly to the destination city, it expends its gravitational potential energy to overcome the friction of the railway.

Since anything that overcomes the static friction of the railway is bound to roll downhill and arrive at its destination, the energy expenditure of this system is:

m*g*h*e

m = mass of train g = 9.8 m/s^2 h = height of departure platform e = efficiency of hydraulic lift

[Of course, the design would have to take into account how far the two cities can be before the incline becomes insufficient for movement]

Any railroad engineers out there to tell me why this deserves a railcar load of fishbones?

 — cowtamer, Apr 19 2007

Wikipedia: 42 http://en.wikipedia...iki/42_%28number%29
For baconbrain and Ian. The well-known number of minutes it takes for a car to fall through a frictionless tunnel to the other side of the earth. [jutta, Apr 20 2007]

gravity train http://en.wikipedia.../wiki/Gravity_train
the wiki entry of this idea [the great unknown, Jun 20 2007]

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A normal train and a GraviTrain have friction working against them all the time. Whether you overcome friction by:
a) continual conversion of chemical energy to kinetic energy; or
b) continual conversion of potential energy to kinetic energy
it's still going to take the same amount of energy.
 — xaviergisz, Apr 19 2007

 I guess the idea is that the energy used to power the elevator can be produced more efficiently and/or environmentally sustainably than the energy that would otherwise be used to power the trains?

This might be so, but I'd have thought the costs of building the inclined tracks would be pretty considerable compared with any gains.
 — imaginality, Apr 19 2007

 32 minutes, I think.

 This idea is not going to be super-efficient. Maybe, just maybe, more efficient that a normal train, but not enough to pay for the fact that it's bloody slow. Time is money.

Building the tracks would cost the moon. [-]
 — baconbrain, Apr 19 2007

One variable you have not considered is wind resistance. Your train that just barely stops in the Abilene station on a calm day is going to stop twenty miles short on a day with a head wind and fly right on through on a day with a tail wind.
 — Galbinus_Caeli, Apr 19 2007

[Galbinus_Caeli] Don't be silly. the track gradient is adjusted according to the wind, obviously.
 — Cosh i Pi, Apr 19 2007

[Rods] You are right and I mentioned this is an annotation to another idea, but I can't seem to find it (perhaps from before the great crash). In Martin Gardner's Annotated Alice, he shows that when Alice falls down the rabbit hole, given a frictionless environment (and a long enough hole) Alice would arrive in Australia in just over 40 minutes. The time taken would be the same for any journey between two places at the same elevation through a straight tunnel.
 — Gordon Comstock, Apr 19 2007

//Alice would arrive in Australia // with a net to catch her hopefully.
 — po, Apr 19 2007

 You've just invented a long-distance version of the railroad "classification yard" or "hump yard". The idea there was that an entire incoming train could be pushed up onto an elevated track, and as each car passes the classification shack, the car is uncoupled, the destination checked, switches set, and the car swoops down off the brow of the hill and is sorted into the correct destination train. Far, far more efficient than having a small locomotive ("switch engine") pick off each individual car and tootle it over to the appropriate track, and make another trip for the next, etc.

 Your advantage would be that if that happened to be an emergency load of powdered mashed potatoes, it doesn't have to wait for the locomotives to come back from Beauford, and get the next train all assembled. Just hoist 'er up and give it a shove to get started, and the single car can make the trip all by itself with no problem.

The next car - milk and butter, probably - could be sent moments later.
 — lurch, Apr 19 2007

////Alice would arrive in Australia // with a net to catch her hopefully //
Or a spring.
 — AbsintheWithoutLeave, Apr 19 2007

 I got the inspiration for this while going down a mountain and playing with my car's MPG meter.

 I ended up driving for about 15 miles burning a negligible amount of gas (99mpg, which is the most the car could display). I figured it could be a lot more efficient to lift something once (and only do the work against gravity) then have to continually push it against the wind resistance, etc.

 Even though the friction that has to be overcome is roughly the same, all that air resistance will do is slow the railcar down--not stop it completely. If you have a queue of railcars, this might make for cheaper transportation.

[Related idea: send smaller packages between two buildings on cablecar-like wires suspended from radio-towers]
 — cowtamer, Apr 20 2007

 // //Alice would arrive in Australia // with a net to catch her hopefully.//

Er no, she just needs a handle to hang on to to stop her plunging back to Oxford. When she falls down the hole she'll keep accelerating (at a decreasing rate of acceleration) until she reaches the centre. From this point she will decelerate (at an increasing rate) until she reaches the surface in Australia where she will be stationary momentarily. Of course she'll be upside down when she gets there, revealing to the uncouth jackeroos her modest victorian camiknickers. A very unsettling experience for a sensitive girl.
 — Gordon Comstock, Apr 20 2007

 "All possible gravity trains on a given planet take exactly the same amount of time to complete a journey (that is, no matter where on the surface the two endpoints of its trajectory are located). For Earth, this time would equal 42 minutes and 12 seconds if it were a perfect sphere."

Thanks, [Jutta].
 — baconbrain, Apr 20 2007

Gravy Trains are baked by the big wigs of British Rail. And also my dog, who eats this idea for breakfast.
 — theleopard, Apr 20 2007

If u wer to use a magnet tunnel there would be zero friction.or get super man to give it a push....no no thats just silly he could just fly it to its destination........ :1 GO SUPER MAN!!!!!!!!!
 — bogeld_mind21, Apr 20 2007

I would agree with the link I put in that this idea would work better on the moon. no air & a solid (non-molten) interior.
 — the great unknown, Jun 20 2007

There is not a single part of this that would be cost effective. Lifting a heavy laden train would take more energy than pushing it. Gas mileage is great on a downhill,but the landscaping involved is insane.
 — Bighongry, Oct 08 2007

Somewhat similar to a funicular railway, except that the trains are not attached to eachother. Actually it's completely different.
 — marklar, Oct 08 2007

//Actually it's completely different.// Yes, but in a very similar way.
 — MaxwellBuchanan, Oct 09 2007

Gravitrain . . . good. Graviplane . . . fantastic (it's called crashing), damn.
 — Brett-Blob, Oct 10 2007

One would have thought that a train coaster would have naturally evolved from roller coasters if they were very practical. Eh, perhaps they could use some rockets in order to slingshot downhill faster than 'g'. [+]
 — quantum_flux, Oct 15 2007

 When I was a student I used to have two paths to university in the hilly city of Jerusalem, for getting there and back home. Each had a short steep climb and then slow decent. Cycling, either way, was a few minutes of strain and then a relaxed downhill 15 minute ride.

As an alternative you could use the funicular paradigm, used in the city of Haifa (Carmelit) and in almost all elevators, where you have only one slope and an opposing counter-weight.[+]
 — pashute, May 21 2008

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