Gravitation


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Topic: Science > Physics
User: "Martin Johansen"
Date: 15 Jan 2005 02:50:52 PM
Object: Gravitation
Hello people.
What mass contributes to the gravitation felt by mass A from mass B?
For example, does the mass from a point higher than the one you are at
contribute to the gravity you feel?
If you know why, is there an explanation for this?
--
_____
New computer algebra system:
http://sourceforge.net/projects/dcas/
My website:
http://www.denotesoftware.com/
.

User: "Old Man"

Title: Re: Gravitation 15 Jan 2005 03:53:59 PM
"Martin Johansen" <mfag@online.no> wrote in message
news:5nfGd.4615$IW4.95121@news2.e.nsc.no...

Hello people.

What mass contributes to the gravitation felt by mass A from mass B?

For example, does the mass from a point higher than the one you are at
contribute to the gravity you feel?

If you know why, is there an explanation for this?

F12 = [ G m1 m2 / | R12 |^3 ] R12
Where R12 and F12 are vectors.
[Old Man]
.

User: "Gregory L. Hansen"

Title: Re: Gravitation 15 Jan 2005 02:58:52 PM
In article <5nfGd.4615$IW4.95121@news2.e.nsc.no>,
Martin Johansen <mfag@online.no> wrote:

Hello people.

What mass contributes to the gravitation felt by mass A from mass B?

For example, does the mass from a point higher than the one you are at
contribute to the gravity you feel?

If you know why, is there an explanation for this?

All masses contribute. But some pull you in different directions than
others, and a mass over your head will decrease your acceleration towards
the Earth. E.g. the Moon and tides.
--
"And don't skimp on the mayonnaise!"
.
User: "Martin Johansen"

Title: Re: Gravitation 15 Jan 2005 03:09:34 PM
"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
news:csc06c$68o$2@rainier.uits.indiana.edu...

In article <5nfGd.4615$IW4.95121@news2.e.nsc.no>,
Martin Johansen <mfag@online.no> wrote:

Hello people.

What mass contributes to the gravitation felt by mass A from mass B?

For example, does the mass from a point higher than the one you are at
contribute to the gravity you feel?

If you know why, is there an explanation for this?


All masses contribute. But some pull you in different directions than
others, and a mass over your head will decrease your acceleration towards
the Earth. E.g. the Moon and tides.

Thanks, one of those aswers which hits you in the face with simplicity
(rightfully so).

--
"And don't skimp on the mayonnaise!"

.

User: "Old Man"

Title: Re: Gravitation 15 Jan 2005 05:01:03 PM
"Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> wrote in message
news:csc06c$68o$2@rainier.uits.indiana.edu...

In article <5nfGd.4615$IW4.95121@news2.e.nsc.no>,
Martin Johansen <mfag@online.no> wrote:

Hello people.

What mass contributes to the gravitation felt by mass A from mass B?

For example, does the mass from a point higher than the one you are at
contribute to the gravity you feel?

If you know why, is there an explanation for this?


All masses contribute. But some pull you in different directions than
others, and a mass over your head will decrease your acceleration towards
the Earth. E.g. the Moon and tides.

The Moon and Earth are both in gravitational free-fall.
Whereas a stationary mass, M, at distance, d, overhead,
acts, with force, F, on test mass, m, according to the
inverse square law of Newtonian gravitation,
F / m = G M / d^2,
the force of the Moon on the test mass is reduced to
that of its gravitational gradient by a factor of (2 R / d)
F / m = ( G M / d^2 ) ( R / d )
where R is the Earth's radius, d is the distance to the
Moon, and M is the Moon's mass.
[Old Man]
.


User: "Mike"

Title: Re: Gravitation 15 Jan 2005 08:10:28 PM
Martin Johansen wrote:

Hello people.

What mass contributes to the gravitation felt by mass A from mass B?

For example, does the mass from a point higher than the one you are

at

contribute to the gravity you feel?

Yes, a small mass in comparison that that of the earth will contribute
virtually nothing or, in Newtonian terms:
If you stand at the surface of the earth (I take the positive direction
being downwards):
F1 = GMm1/r^2 (1), m1 = your mass, M = mass of the earth, F1 is the
downward gravity force on you.
A mass m2 is at distance h above you:
F2 = -Gm1m2/h^2 (2) is the force between m1 and m2
F2 is the upward gravity force on you.
(1), (2) ---> F1/F2 = - (Mh^2)/(m2r^2) (3)
For instance, for a 100 Kg mass m2 and h = 1 m, given that M ~ 6.0 x
10^24 Kg, r ~ 6.4x10^6 then from (3) ---> F1/F2 ~ 1.5 x 10^9
that is the force the 100 Kg mass affects on you is about 1.5 billion
times smaller than the gravity force between the earth and you.
Mike


If you know why, is there an explanation for this?

--
_____
New computer algebra system:
http://sourceforge.net/projects/dcas/
My website:
http://www.denotesoftware.com/

.

User: "Sam Wormley"

Title: Re: Gravitation 15 Jan 2005 02:57:35 PM
Martin Johansen wrote:

Hello people.

What mass contributes to the gravitation felt by mass A from mass B?

For example, does the mass from a point higher than the one you are at
contribute to the gravity you feel?

If you know why, is there an explanation for this?

Use F_g = G m1 m2 / r^2
Background;
http://scienceworld.wolfram.com/physics/Gravity.html
Planetary Motion
http://scienceworld.wolfram.com/biography/Kepler.html
http://scienceworld.wolfram.com/physics/LagrangesPlanetaryEquations.html
The theory of general relativity describes the phenomenon of gravity very differently:
http://scienceworld.wolfram.com/physics/GeneralRelativity.html
General Relativity Tutorial by John Baez
http://math.ucr.edu/home/baez/gr/gr.html
Observational and Experimental Evidence Bearing on General Relativity
http://math.ucr.edu/home/baez/RelWWW/tests.html
.


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