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[LONG] Consulting the Oracle a la Hake (was "zero" gravity)

At 18:19 7/2/01 -0400, Dwight Souder wrote:

Hello everyone. I hope all of you are enjoying your summer. I was wondering
if someone could please help me out? I have forgotten the name of a
phenomenon and it has been driving me crazy!
///
Technically, whenever you have a mass in space, no matter how far
away you get from that object, there is always a little bit of a
gravitational
pull.
///
In other words, if the earth and moon were 2 fixed objects (the only objects)
in space and somewhere in between (a little closer to the moon side), a 3rd
object at a certain point would be pulled with equal magnitude and in
opposite
directions. Therefore, the 3rd object, if it wasn't moving to begin with,
would not move to either of the other larger objects due to vector sums of
the
gravitational pull equaling zero.

Does anyone know of the name of this? I was discussing this with a fellow
science teacher and we were both racking our brains trying to remember what
this was called.

Thank you,
Dwight Souder
--------------------------------------------------------------------

Although several people provided fast responses to Dwight's immediate
question, I recall that Richard Hake has been nagging the list about
making more use of the collective wisdom.

I recall finding the NAU web presence for phys-l and hitting the
'search archive' choice, at some point.
But I finally realised that the dream of instant results is
easily realised with the following terse command to the listbot.

An email is addressed to LISTSERV@lists.nau.edu
The subject line is unnecessary.

The first line of text is to say simply:
search phys-l <some keyword>
end

[Finding an appropriate keyword is still the crux, however!]

You wait 15 seconds, call down fresh mail, and see the tireless
bot's instant response, like this one:

From: "L-Soft list server at LISTS.NAU.EDU (1.8d)"
<LISTSERV@lists.nau.edu>
Subject: Output of your job "inet"
To: Brian Whatcott <inet@INTELLISYS.NET>

search phys-l lagrange
end

-> 52 matches.

Item # Date Time Recs Subject
------ ---- ---- ---- -------
000065 96/03/23 07:38 24 comet
001609 96/07/17 10:31 36 Re: momentum before force
004253 97/02/19 15:04 30 SOHO orbit
004256 97/02/19 15:40 7 Re: SOHO orbit
004258 97/02/19 17:44 31 Re: SOHO orbit
004259 97/02/19 18:06 32 RE: SOHO orbit
004260 97/02/19 18:12 82 Re: SOHO orbit
004261 97/02/19 18:43 57 Re: SOHO orbit
004280 97/02/20 17:49 27 SOHO you're welcome (was: SOHO Thanks)
004282 97/02/20 18:20 23 Re: SOHO Thanks
004620 97/03/03 17:58 37 Re: Bulges
005103 97/03/26 17:25 61 RE: reflections on a neglected problem
006237 97/06/04 10:39 88 Interactive Physics and Lagrange points
006578 97/07/12 15:39 53 periodic accelerated potential
008683 97/11/05 15:22 56 Re: Models, etc./Higher derivatives
008872 97/11/15 11:25 50 RE: Forces
009021 97/11/20 05:24 36 Re: That jerk again!

/I cut out all responses from 1998, 1999, & 2000/

028065 01/01/19 10:34 34 Global Energy etc.
028067 01/01/19 10:40 48 Re: Global Energy etc.
028069 01/01/19 10:56 40 Re: Global Energy etc.
028070 01/01/19 10:55 52 Re: Global Energy etc.
028076 01/01/19 11:51 29 Re: Global Energy etc.
028088 01/01/19 11:46 35 Re: Global Energy etc.
028090 01/01/19 14:50 44 Re: Global Energy etc.
028102 01/01/19 17:48 55 Re: Global Energy etc.
028117 01/01/20 01:20 63 Re: Global Energy etc.
028153 01/01/21 16:16 35 Re: Global Energy etc.
028169 01/01/22 13:42 50 Re: Global Energy etc.
030986 01/06/30 16:42 54 Re: are normal reaction and tension
conservative ?
031017 01/07/02 15:44 69 Re: "zero" gravity
031018 01/07/03 08:49 57 Re: "zero" gravity


*** Not only does the bot supply the references, but it formulates a
command which will call them all (Ouch!) You could easily cut the numbers
down to just a sampling....
...it says:

To order a copy of these postings, send the following command:

GETPOST PHYS-L 65 1609 4253 4256 4258-4261 4280 4282 4620 5103 6237 6578
8683 8872 9021 10716 11349 11468 11473 14669 14675 15394 17719 17735 17745
17747 18883 19961 19963 20446 20616 21388 26490 26718 26876 26881 28065
28067 28069-28070 28076 28088 28090 28102 28117 28153 28169 30986
31017-31018


***And then, to top it off, it offers a sampler of each resonse.
What could be more helpful?


Item #65 (23 Mar 1996 07:38) - comet
viewing from home 5 miles North of Pine Mountain, GA(population 1,000)
15 miles South of LaGrange, GA, population 60,000.
^^^^^^^^
30 miles North of Columubus, GA, population 250,000)

Item #1609 (17 Jul 1996 10:31) - Re: momentum before force
resisted for some time during the development of classical mechanics.
Lagrange was so proud of the idea that he wrote about it at great
^^^^^^^^
length in the beginning of the Mechanique Analytique.

Item #4253 (19 Feb 1997 15:04) - SOHO orbit
been reading about the SOHO spacevehicle. It has been inserted in an orbit
about the Sun at a Lagrange point ( defined as a point where Sun's Gravity
^^^^^^^^
and Earth's Gravity fields balance). The press release I just read from the
***************

Here I have trouble: Is the net force at the Lagrange point zero? If so,
^^^^^^^^
how does it manage to orbit at all? Is it not an unstable equilibrium?

Item #4256 (19 Feb 1997 15:40) - Re: SOHO orbit

One needs more than two bodies for a Lagrange point.
^^^^^^^^

Item #4258 (19 Feb 1997 17:44) - Re: SOHO orbit
Ken,
There are five Lagrange points. The most obvious being the point
^^^^^^^^
being the one on the line joining the centers of the objects where the force
***************
...
Here I have trouble: Is the net force at the Lagrange point zero? If so,
^^^^^^^^
how does it manage to orbit at all? Is it not an unstable equilibrium?

Item #4259 (19 Feb 1997 18:06) - RE: SOHO orbit
been reading about the SOHO spacevehicle. It has been inserted in an orbit
about the Sun at a Lagrange point ( defined as a point where Sun's Gravity
^^^^^^^^
and Earth's Gravity fields balance). The press release I just read from the
.
.
.

***///snippety snip - I cut out the vast majority of samples on this
keyword///

.
.
.
.
Item #28065 (19 Jan 2001 10:34) - Global Energy etc.
a set of obiting reflectors. Another is to block 2% of the sun's
radiation with a single big reflector at the SOHO Lagrange position.
///

Item #28076 (19 Jan 2001 11:51) - Re: Global Energy etc.
Rick your calculation and fear of shadows is irrelevant for the
Lagrange point Chuck mentioned. Your calculation is only for a blocking
^^^^^^^^
shield that is very close to the Earth's surface. Any solar blocking
shield located at the apropriate Lagrange point that blocked 2% of the
^^^^^^^^
solar radiation would appear as a permanent sunspot on the solar disk of

Item #28088 (19 Jan 2001 11:46) - Re: Global Energy etc.
a one year orbital period. Because that point is not one of stability in
the Lagrange scheme, and because the real Earth's orbit is eccentric, the
^^^^^^^^
reflector's position would have to be controlled by rockets. Fuel

Item #28090 (19 Jan 2001 14:50) - Re: Global Energy etc.
a set of obiting reflectors. Another is to block 2% of the sun's
radiation with a single big reflector at the SOHO Lagrange position.
^^^^^^^^


Item #28102 (19 Jan 2001 17:48) - Re: Global Energy etc.
Because that point is not one of stability in
the Lagrange scheme, and because the real Earth's orbit is eccentric, the
^^^^^^^^
reflector's position would have to be controlled by rockets. Fuel

Item #28117 (20 Jan 2001 01:20) - Re: Global Energy etc.
> Because that point is not one of stability in
the Lagrange scheme, and because the real Earth's orbit is eccentric, the
^^^^^^^^
reflector's position would have to be controlled by rockets. Fuel

Item #28153 (21 Jan 2001 16:16) - Re: Global Energy etc.
idea to do stationkeeping for a probe/satellite/shield etc. placed at
the L1 Lagrange point between the Earth and the Sun without using any
^^^^^^^^
rocket/thruster fuel by regulating its solar reflectivity, and extended

Item #28169 (22 Jan 2001 13:42) - Re: Global Energy etc.
idea to do stationkeeping for a probe/satellite/shield etc. placed at
the L1 Lagrange point between the Earth and the Sun without using any
^^^^^^^^
rocket/thruster fuel by regulating its solar reflectivity, and extended

Item #30986 (30 Jun 2001 16:42) - Re: are normal reaction and tension
conservative ?

http://webug.physics.uiuc.edu/courses/phys326/spring01/lectures/lagrange_
^^^^^^^^
http://webug.physics.uiuc.edu/courses/phys326/spring01/lectures/lagrange_2/t
^^^^^^^^
sld003.htm

Item #31017 (2 Jul 2001 15:44) - Re: "zero" gravity
influence the two massive bodies. In the case of perfectly
circular orbits there are five positions, known as the "Lagrange
^^^^^^^^
Points," in the rotating frame at which the third body can be
***************
You will find more than you ever wanted to know by searching on
"Lagrange Points" or "Restricted three-body problem."
^^^^^^^^

Item #31018 (3 Jul 2001 08:49) - Re: "zero" gravity

It is not exactly what you describe but do you mean the Lagrange Points?
^^^^^^^^

"The Lagrange Points mark positions where the gravitational pull of
^^^^^^^^
the two large masses precisely equals the centripetal force required

end
Remaining commands ignored.

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brian whatcott <inet@intellisys.net> Altus OK
Eureka!