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"I was perfectly satisfied to write science fiction knowing that it would pay very little, that it would be seen by only a very few people."
- Isaac Asimov
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| Gravity-assisted Subway | ||
| The fastest way between continents (that does not entail leaving the ground). |
This piece of technovelgy gives a great illustration of the fastest way to get from point A on the surface of the earth to another surface point B.
| The car shot forward and down. Corbell was on a roller coaster. He pulled out a chair arm and hung on. The car fell at a slant for what felt like half a minute. Then there was high gravity as car and tunnel curved back to horizontal. Light inside, darkness outside. Corbell was beginning to relax when the car rolled, surged to the left; rolled, surged to the right, steadied. What was that? Changing tunnels? His ears popped. Peerssa spoke. "Your speed is in excess of eight hundred kilometers per hour and still accelerating. A remarkable achievement. "How do they do it?" "At a guess, you are riding a gravity-assisted linear accelerator through an evacuated tunnel. You are about to pass beneath the Pacific Ocean..." |
| Technovelgy from A World Out of Time,
by Larry Niven. Published by Random House in 1976 Additional resources -
|
The ingenious solution is to dig a tunnel from one point to the other, using the force of gravity to provide some of the acceleration. The beauty of this approach is that, in a frictionless environment, you can speed the train on its way without having to apply any energy - and slow it down the same way!
The questions (for you engineers) are: what is the best shape (or curve) for the tunnel, and how can you avoid those pesky underground temperatures and pressures? See this article on the brachistochrone problem, one of the earliest problems posed in the calculus of variations. Newton solved this problem from scratch in one day in 1696; got your pencil? Ready, set ... go!
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'The massive feet working the pedals, arms and hands flashing and glinting...'
'There were cubic miles of it, and it glistened like a silvery Christmas tree...'
'Jason had been guiding the caravan of cars as usual...'
"The robot solemnly hit a ball against the wall, picked it up and teed it, hit it again, over and again...'
'There was a wall ahead... It was riddled with holes that were the mouths of tunnels.'
'...support the interior human structure against Jupiter’s pull.'
'Anything larger than a BB shot it picked up and placed in a tray...'
