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DivideByZero

Posted: Sun Jul 13, 2008 7:12 am Post subject: Gravity

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Please see image here: http://img390.imageshack.us/img390/5566/boxgravityhc5.jpg

How many boxes are required for the gravitational phenomenon to occur.

In other words, if I continued adding more and more boxes (not touching each other) when will they start connecting together because of their own gravity?
EDIT: assume this is occuring initially in a zero gravity vacuum.

Last edited by DivideByZero on Sun Jul 13, 2008 8:29 am; edited 1 time in total

Harold14370

Posted: Sun Jul 13, 2008 7:24 am Post subject:

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As soon as you add some mass, it is no longer a zero gravity vacuum.

William McCormick

Posted: Sun Jul 13, 2008 7:42 am Post subject: Re: Gravity

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DivideByZero wrote:

If this was occurring in a vacuum in space with no gravity or free falling. The type of material and ambient radiation present would probably determine if the boxes moved together or apart.

Sincerely,

William McCormick
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DivideByZero

Posted: Sun Jul 13, 2008 8:27 am Post subject:

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Harold14370 wrote:

As soon as you add some mass, it is no longer a zero gravity vacuum.

oh sorry about my wording. It is initially zero gravity. You add the boxes afterward.

William McCormick wrote:

If this was occurring in a vacuum in space with no gravity or free falling. The type of material and ambient radiation present would probably determine if the boxes moved together or apart.

Why would it move apart?

.

William McCormick

Posted: Sun Jul 13, 2008 9:19 am Post subject:

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DivideByZero wrote:

Harold14370 wrote:

As soon as you add some mass, it is no longer a zero gravity vacuum.

oh sorry about my wording. It is initially zero gravity. You add the boxes afterward.

William McCormick wrote:

If this was occurring in a vacuum in space with no gravity or free falling. The type of material and ambient radiation present would probably determine if the boxes moved together or apart.

Why would it move apart?

.

If not properly shielded in space, an electromagnetic field could be produced. The same field that plays havoc with the atomic clock.

Depending upon the material the block is made of, it could attract or repel.

Sincerely,

William McCormick
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Harold14370

Posted: Sun Jul 13, 2008 9:47 am Post subject:

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DivideByZero wrote:

oh sorry about my wording. It is initially zero gravity. You add the boxes afterward.

Any two masses will attract one another by their gravitational fields in proportion to their masses and the universal gravitation constant G and inversely proportional to the square of the distance between. Lemme try that tex thingie

$F = G \frac{m_1 m_2}{r^2}$

Alc

Posted: Mon Jul 14, 2008 5:56 pm Post subject:

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well, gravity from every object in space, including ourselves adds to vast gravitational feild, when near a celestial body or any body, the feild appears uniform, which means the gravity is at its strongest, the further you travel from an object, the feild becomes radial by comparrison (even though the gravity is initally fro the same point of an object a radial feild can appear uniform in any circumstance but never is).

As Harold14370 just mentioned. Inverse square law of gravity is basically, if you double the distance between two bodies, the gravity will quater in strength.

For the boxes to move together it would have to be 0 gravity before the boxes are added, then i don't see why they wouldnt, it would be very slow, assuming the boxes are quite lightweight.

In the same way anything in 0 gravity can orbit something equal in size or larger than itself, im not too sure if a larger object can be pulled into orbit of something already in a fixed orbit? say jupiter orbiting earth... im not sure about that. anyone?

the boxes themselves each produce equal gravity, and assuming its a vast network of boxes they would all move towards the center of the overall gravitational feild produced, But, assuming its an infinite network of boxes each EXACTLY the same distance from each other, i beleive theyd al be pulled equally in each direction... and at the other extreme, im not sure if random groups of boxes would start to form.

I didnt quite answer your question i know... but im guessing the answer in 0 gravity is 2.

grecinos2

Posted: Mon Jul 14, 2008 11:01 pm Post subject: Re: Gravity

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Joined: 19 May 2008
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I've been working on this crude project for the past 2 weeks or so. It demonstrates how massive objects in space affect one another. It does not include collision detection but rather gravity deflection.

It was written as a java applet. It has a crude interface without error checking, so be forewarned. You can modify the size of the "debris field" with the 2 text fields towards the top (x,y respectively). You may want to turn off "Draw Tails" by clicking on that checkbox. The simulation begins to get slow once you reach the 1000 satellite count point. One last thing is that you can add "Planetoid" sized objects by clicking and dragging the cursor anywhere on the window. This is somewhat gimped by the fact that I wanted to make it feasible to insert a Planetoid by single clicking.... I'm rusty at java and haven't figured that out yet.

The Visible area is around 1600x1024 +/- a few....so set your screen size appropriately.

Warning: you shouldn't keep it running for a long time as it is prone to lockup after 10-20 mins of continuous iterations. If this happens then just halt the app using the Task Manager. BE SURE TO SAVE YOUR WORK IN PROGRESS BEFORE USING THIS APPLET.

Let me know if it works for you...you may need to install the lastest Java Client at www.java.com.

EDIT: Sorry I forgot to include the URL... Here it is:
http://www.grecinos.net/fun/bounce/bounce.html

-grecinos

DivideByZero wrote:

DivideByZero

Posted: Tue Jul 15, 2008 4:21 am Post subject: Re: Gravity

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grecinos2 wrote:

woah I like your java applet.
What was the algorithm/math you used?

Janus

Posted: Tue Jul 15, 2008 11:13 am Post subject:

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Alc wrote:

In the same way anything in 0 gravity can orbit something equal in size or larger than itself, im not too sure if a larger object can be pulled into orbit of something already in a fixed orbit? say jupiter orbiting earth... im not sure about that. anyone?

Technically, no object orbits another, instead they both orbit their common center of gravity or barycenter. The barycenter will be located at a point closer to the center of the greater mass. For instance, the Earth-Moon barycenter is located some 1600 km below the surface of the Earth. The Sun-Jupiter barycenter is located some 82,552 km above the Suns surface. With a Jupiter-Earth orbital arrangement, the barycenter would always be closer to Jupiter's center.

Quote:

the boxes themselves each produce equal gravity, and assuming its a vast network of boxes they would all move towards the center of the overall gravitational feild produced, But, assuming its an infinite network of boxes each EXACTLY the same distance from each other, i beleive theyd al be pulled equally in each direction...

Actually, the boxes would collapse towards each other. The reason for this is Newton's shell theorem. In it, he showed that the gravity from a uniform hollow shell would be zero everywhere in the hollow.

This applies to this situation thusly. Imagine any given finite spherical volume of our box-filled space surrounded by an infinite volume of box filled space. This surrounding volume can be treated and a series of uniform hollow shells nested inside of each other. Each shell, by Newton's theorem, has no gravitational effect on anything inside of it. Thus the boxes within our given spherical volume feel no net gravitational effect from any of the boxes in the volume surrounding it. They only feel the gravitational effect of the boxes within the given volume. This gravitational effect causes the boxes to draw together.

Ergo, even in an infinite universe filled with uniformly placed boxes, the boxes will draw together.
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Alc

Posted: Tue Jul 15, 2008 12:14 pm Post subject:

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first ive heard of this barycenter jargen, thanks janus, ill look into that one.

Also please note theres nothing mentioned about the boxes being hollow, although rediculous of me to assume otherwise i suppose, but if the objects were to have a solid center, im sure it would be a different matter. Smile

Janus

Posted: Tue Jul 15, 2008 1:23 pm Post subject:

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Alc wrote:

I wasn't talking about the boxes being hollow, read my post again.
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Pong

Posted: Tue Jul 15, 2008 4:07 pm Post subject:

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Janus wrote:

Ergo, even in an infinite universe filled with uniformly placed boxes, the boxes will draw together.

No, infinity has no center.

grecinos2

Posted: Tue Jul 15, 2008 9:56 pm Post subject: Re: Gravity

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Joined: 19 May 2008
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Thanks for the compliment. I used standard Newtonian Physics.... Essentially everything (except for the tails) in the simulation has mass and the attration to eachother can be measured by the formula (if I remember correctly) F=G(M1M2)/r^2

It gets real neat when you play with the numbers on the applet.... Say 50 X 10.

I forgot to mension in my previous post that the simulation takes place only on a 2 dimensional plain...

DivideByZero wrote:

woah I like your java applet.
What was the algorithm/math you used?

DivideByZero

Posted: Wed Jul 16, 2008 4:13 am Post subject: Re: Gravity

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Joined: 02 Dec 2007
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grecinos2 wrote:

DivideByZero wrote:

woah I like your java applet.
What was the algorithm/math you used?

Would making a 3d model of your applet be a lot harder? Are there any tutorials online for java for creating 3d graphics in java. I really want to make a planetary model and customize it to see what happens.

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