Talk:Gravity train

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The error has now been corrected (see previous version of talk page).--New Thought 10:16, 6 September 2005 (UTC)

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[edit] Discussion

Dumb idea, what about the magma?

That's why it's a "theoretical" means of travel.

How does the earth's rotation affect the line of travel? Particularly when the train would travel east/west as opposed to directly north/south. 207.245.73.241 13:53, 9 October 2006 (UTC)

The comment "Evacuating the air to eliminate drag would require additional power." seems to over-state the difficulty of such a task. Once an extremely strong sealed pipe has been 'laid' through the earth, evacuating it and providing airlocks at each end seems a relatively trivial engineering feat. In fact it would probably be required to avoid the immense air pressure at the bottom of the hole (or even to stop it liquefying?).

I assumed, but didn't know the Gravity Train concept had been thought of before. As a kid I used to think about such things. I only considered the hole through the middle of the earth, the entire journey would be weightless. It seems to be on the limits of physical practicality, the main problem being the immense pressure (and currents), not the temperature which is (probably) much more reasonable. Perhaps someone could expand on just how immense this pressure is.

It's similar to my low earth orbit idea, where an evacuated pipe is laid on or under the sea, and vehicles are accelerated to mach 22 (or whatever LEO speed is) inside this pipe, where they will levitate naturally. It would take the same time to get to the other side, and assuming the energy is recovered, also lossless (and weightless of course). Again, not the safest form of travel. --Adx 01:31, 23 October 2006 (UTC)

I don't think the trip would be weightless, unless the trip was directly through the centre of the world. The gravity vector would be on an angle which could be resolved into two forces only one of which would provide forward motion, the other would still act perpendicular to that motion. The ratio of those forces would make you weigh less, but not weightless. Vespine 02:47, 8 February 2007 (UTC)

In my last paragraph I was referring to an orbital trajectory (weightless by definition), only at the surface of the earth rather than slightly above it (low earth orbit). Probably "ballistic trajectory" is the better term. One example goes around the earth, the other straight through it. I hadn't thought about it, but it should be possible to have a weightless trip using any mix of these two paths, provided you are shot down the hole with some initial speed. For example, if the path bent so that at the midpoint of your trip you were halfway between the surface and the centre, then you would be orbiting what was effectively a half diamater earth at that point. I wonder what the path would look like. --Adx (talk) 15:02, 22 November 2007 (UTC)

[edit] The other Gravity Train

The non theoretical gravity train also needs an entry. It was used a lot in the 1800's a horse would pull several cars to the top of a hill, it would be loaded with cargo and the train would coast down the hill with a brakeman or two (and the horse - see Dandy waggon). Does anyone have thoughts on if both should be discussed in this article or if they should have separate articles and if separate how to handle the disambiguation? Jeepday 03:59, 19 November 2006 (UTC)

I think they should have separate articles. Probably call your article on the other practical one "Gravity train" because that seems to be the definite name of it. But I dunno what the best name for this theoretical article is. Took me a while to find that this article actually existed. As for disambiguation, all we'd need is links at the top of each article. There are templates, have a look at Wikipedia:Disambiguation. Vadmium 14:27, 17 June 2007 (UTC)

We already have an article, see Gravity railroad. Biscuittin 12:44, 4 November 2007 (UTC)

[edit] external links

I just thought I would add an external links section
will add this link
http://www.damninteresting.com/?p=696
--Mrebus 19:46, 17 October 2006 (UTC)

[edit] Important Fact Ignored?

Since gravity is a function of mass and distance from the center of gravity of that mass, an interesting thing would happen at the center of the earth: If you could hollow out the center, and position yourself in the hollow space, you would be pulled simultaneously in all directions, and float weightless.

What I'm wondering, is whether the acceleration assumed by the takes this into account. We think of acceleration due to the earth's gravity to be 32 feet/second/second, but this is not constant. As you proceed toward the center of the earth, the mass above you increases, and begins to offset the gravitational pull of the mass below you. As a result, the rate of acceleration will decrease over time.

Any thoughts on this?

hubby2debbie--Hubby2debbie 03:36, 5 December 2006 (UTC)

I believe that's why the train accelerates until it's in the center, and then decelerates until it comes to a stop at the other side. Something like a parabolic acceleration but with one side negative. -72.87.188.204 19:20, 11 February 2007 (UTC)

[edit] Solid moon

Several articles, such as Moon and Lunar_Laser_Ranging_Experiment both say the moon has a liquid core. -72.87.188.204 19:15, 11 February 2007 (UTC)

[edit] "and Wes"?

Robert Hooke and Wes? Wes who? —The preceding unsigned comment was added by 66.27.69.167 (talk) 04:05, 9 March 2007 (UTC).