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Me and my friend are having a debate on whether it would be possible for a human to travel at 15,000 miles an hour from London to Australia in the matter of 90 minutes. Would a human be able to survive travel in such at fast speeds knowing he will have to overcome immense amount of g's. Basically is it possible for a human? or will he suffer death in the process?

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Think ICBM. Think the Mercury launches. Or as Heinlein called it "semi-ballistic". –  dmckee Feb 3 '13 at 2:17
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G-forces have nothing to do with high speeds. G-forces have to do with acceleration--with changing speeds. I don't think this question is really about how fast someone's going. Rather, it's about how they get going that fast. What kind of acceleration mechanism do you have in mind? –  Muphrid Feb 3 '13 at 6:11
    
Concerning radial acceleration, you needn't worry about leaving your seat. Only at speeds of roughly 17,686 mph along the earth's (assumed smooth) surface will you become "weightless". And only at 25,012 mph you will experience -1 G while stuck to the roof of your vehicle. Above 30,633 mph you might want to sit upside down, because otherwise you will potentially experience redout and death. –  Glen The Udderboat Feb 3 '13 at 22:30

2 Answers 2

The distance from London to Australia is about 17,000km. If you wanted to minimise the acceleration you'd feel during the trip you'd accelerate continuously for the first half of the journey (8,500km) then decelerate at the same rate for the second half. To work out what acceleration is required you use the SUVAT equation:

$$ s = ut + \frac{1}{2}at^2 $$

For half the journey the distance $s$ is 8,500km and the time $t$ is 45 minutes (2700 seconds), so using the above equation the acceleration required is about 2.33m/s$^2$, which is only about a quarter of a $g$. The only trouble is that your speed at the halfway point would be about 6,300m/s (about Mach 18), so you'd need a rocket rather than a plane to do it.

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Gagarin flew around the world in 90 minutes 50 years ago, apparently without serious health problems.EDIT: OK, it was 108 minutes.

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I always wonder wether it would be much more expensive (in terms of fuel) to have sort of a ballistic civil transport between continents... It would be awesome: some minutes quickly rising, then one hour or so (depending upon your destination) of absolute silence with an amazing sight of the outer space and feeling weigthless (some passengers vomiting...) and eventually re-entering the troposphere with clouds and blue sky before landing... –  Eduardo Guerras Valera Feb 3 '13 at 12:44
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@Eduardo Guerras Valera: It is my understanding that intercontinental ballistic transport would be much more expensive with current technology - the costs would not be much lower than those for orbital flights (see the latter costs in the following relatively old source: futron.com/upload/wysiwyg/Resources/Whitepapers/… ). However, some future technologies might change this situation (e.g., good.is/posts/can-nasa-launch-a-rocket-with-a-laser ). –  akhmeteli Feb 3 '13 at 14:05
    
Nice link! (+1), I was just talking this morning with my father about hypothetical wireless power transmission possibilities. That lasers/masers in your link were one of the possibilities, although it has thermodynamic limitations, since the rocket is nearly isolated (but in your link they overcome this by using the laser power to vaporize a metal, so the temperature would not rise as long as there were some solid metal left). Very interesing... –  Eduardo Guerras Valera Feb 3 '13 at 18:01

protected by Qmechanic Feb 6 '13 at 22:23

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