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# Re: Re: The GZG Digest V2 #1753

From: Roger Burton West <roger@f...>
Date: Fri, 3 Oct 2003 16:08:27 +0100
Subject: Re: Re: The GZG Digest V2 #1753
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On Fri, Oct 03, 2003 at 10:50:43AM -0400, laserlight@quixnet.net wrote:
>>Also would be useful to remember the Lagrange 1 point (between the
Earth and
>Moon, or the Sun and the Earth, &cet.), where the local gravitational
force
>is essentially null. There would be a region around this point where
the net
>force would be beneath the threshold you specify. These points exist
>throughout the solar system, and are in constant motion! Have fun...
:-)
>
>Good throught!  Hadn't occurred to me at all--you win today's Sneaky
Player award.

Well, the Lagrange points aren't exactly points of neutral gravity;
they're points of balance between gravity and centripetal force. (And
L1-L3 are "peak" points, i.e. something put there will drift away, where
L4-L5 are "troughs" and will correct small drifts.)

There is, for any pair of bodies, a point where the gravitational
attractions of the two cancel out - the ratio being that of the square
roots of the masses. For Earth-Sun, I make this about 260,000km from the
centre of Earth.

Whether this condition of space allows you to jump in or out is another
matter. My own inclination is that this sort of thing is what one's
aiming for when attempting a jump within the limit - a small patch of
space where conditions might be suitable. But it's small enough that
it's still very risky...

Roger
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