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What is gravity ?

Posted by: Rolf Guthmann - Fri Dec 02, 2005 7:57 pm
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What is gravity ? 
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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Wed Jan 11, 2006 10:13 pm
:roll: I know I am going to regret this, but...

SuperShuki wrote:
If something in orbit gets pushed closer to the sun, in relation to a line drawn from the sun to the object, the gravity will increase.


Consider the logical opposite. If something in orbit gets pushed FARTHER from the sun in relation to a line drawn from the sun to the object, the gravity will decrease, right? If so, would you say that the object would spiral away from the sun?


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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Thu Jan 12, 2006 12:55 am
campbelp2002 wrote:
:roll: I know I am going to regret this, but...

SuperShuki wrote:
If something in orbit gets pushed closer to the sun, in relation to a line drawn from the sun to the object, the gravity will increase.


Consider the logical opposite. If something in orbit gets pushed FARTHER from the sun in relation to a line drawn from the sun to the object, the gravity will decrease, right? If so, would you say that the object would spiral away from the sun?


Sure! Prove me wrong. :D

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Post    Posted on: Thu Jan 12, 2006 2:38 am
Give it up Campelp2002, you know that Super' is either totally ignorant and not interested in finding out the truth :( , or is simply stringing you along by pretending to be so.
I hope that it's that latter but I'm afraid that Super' is hell bent on displaying a level of ignorance shown to belong to the majority of the human species and responsible for the parlous state of the world today :( :(
I personally have no problems with ignorant people (hell everyone is in some way or other), where I take issue is with ignorant people who should know better or aren't interested in taking the trouble to educate themselves. Orbital mechanics isn't intuitive and thinking it is leads to eroneous conclusions as so ably demonstrated in Super's blog. Good luck Super'. If you are being serious then you're going to need it. :lol:

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Post    Posted on: Thu Jan 12, 2006 3:11 am
Actually, it *is* intuitive. If you get it, you got it. If you don't, you won't. That simple.

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Post Spiraling outwards   Posted on: Thu Jan 12, 2006 3:44 am
The case of the orange in orbit: you throw the orange to a high enough orbit, it appears to stay there.

The case of the Planet in orbit: you throw the Planet to the higher orbit, with the same acceleration as you threw the orange, and it'll keep going like the energizer bunny. Why? Because the force is greater than gravity. What is the countervailing force working against gravity? Momentum! When Intertia times mass is greater than the combined forces of gravity holding the planet in orbit, bye' bye' planet!

This is how the Big Bang worked, by the way. With a big enough Bang, it just keeps going and going and going . . .

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Post    Posted on: Thu Jan 12, 2006 3:50 am
beancounter wrote:
Give it up Campelp2002, you know that Super' is either totally ignorant and not interested in finding out the truth :( , or is simply stringing you along by pretending to be so.
I hope that it's that latter but I'm afraid that Super' is hell bent on displaying a level of ignorance shown to belong to the majority of the human species and responsible for the parlous state of the world today :( :(
I personally have no problems with ignorant people (hell everyone is in some way or other), where I take issue is with ignorant people who should know better or aren't interested in taking the trouble to educate themselves. Orbital mechanics isn't intuitive and thinking it is leads to eroneous conclusions as so ably demonstrated in Super's blog. Good luck Super'. If you are being serious then you're going to need it. :lol:


If you really have the Truth, go ahead and prove it! I'll be glad to accept that things can't spiral into the sun/planet-if you can convince me. Remember, orbital Gravity is the sum of two forces- the sun pulling on the planet and the planet pulling on the sun.

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Post    Posted on: Thu Jan 12, 2006 6:22 am
Hi Super',
The truth has already been explained. You don't wish to think it through, work it through and in the end, prove it for yourself. That's the real issue and nothing I say here is going to change that. :( What I can say is that I did not arrive at the answer in a pure mathematical way. But I had it explained to me, understood what the issues were and realised the truth. Sorry, you'll have to work it out for yourself like everyone else who gets it. :)

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Post    Posted on: Thu Jan 12, 2006 9:14 am
SuperShuki wrote:
If you really have the Truth, go ahead and prove it! I'll be glad to accept that things can't spiral into the sun/planet-if you can convince me. Remember, orbital Gravity is the sum of two forces- the sun pulling on the planet and the planet pulling on the sun.


It already has been proven by many others, all you have to do is some research.... I think this is your problem now, not ours.
I could make a physics demo, where you can throw an orrange, and see if it hits the planet, or can first make an orbit, and than still hit it or not... but since there're so many people unable to understand it... it would cost too much time to educate them all ;) So no physics demo for you :P

But hey... The first time I thaught about it.. I would say it was possible, until I actually started thinking ;) and than I realised it's just not possible.. so maybe you still have to prove something to yourself 8)

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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Thu Jan 12, 2006 2:02 pm
SuperShuki wrote:
Sure!
OKaaaaaaaaaay...
You might want to notify NASA and others of your discovery. They could do stuff like send the ISS to the moon by just giving it a little push that way and letting it spiral up. Would save a lot of propellant compared to thrusting up to escape velocity.


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Post    Posted on: Thu Jan 12, 2006 3:11 pm
SuperShuki: I'm seriously getting the feeling that you're just trying to be cute (again), and failing miserably (again).

I might politely point out that the other people who refused to accept reality, and attempted to convert others to their own surreality (I'm thinking of Odyssey Spacelines, BRN, the so-called International Space Agency, and Franklin Ratliff) were all banned with full support of the board community. You're starting to seriously annoy some people, Shuki. Just so you know.

Now, to your credit, you've restrained yourself to irritating people on one thread at a time, and haven't gone and spammed the whole board. You've also refrained from insulting/attacking one of the mods or admins. (and so are not a candidate for banning -- yet) But you're still being annoying. Please stop.

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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Thu Jan 12, 2006 7:43 pm
campbelp2002 wrote:
SuperShuki wrote:
Sure!
OKaaaaaaaaaay...
You might want to notify NASA and others of your discovery. They could do stuff like send the ISS to the moon by just giving it a little push that way and letting it spiral up. Would save a lot of propellant compared to thrusting up to escape velocity.


A big enough push will send it to the moon, where it will be captured by the moon's gravity and will spiral in.
Why don't you just make an animation with the numbers plugged in?

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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Thu Jan 12, 2006 8:49 pm
SuperShuki wrote:
A big enough push will send it to the moon
Big enough? You think there is some lower limit below which the extra speed works differently? If a big push gets it spiraling up fast, wouldn't a small push get it spiraling up slowly? Either way, according to your thinking, wouldn't it eventually get to the Moon?

If you want numbers, my numerical orbit simulations are still online.
http://home.austin.rr.com/campbelp/astro/orbit.xls
and
http://home.austin.rr.com/campbelp/astro/orbit.html


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Post Your thinking-my thinking   Posted on: Thu Jan 12, 2006 10:19 pm
This is what I think you are thinking:
http://members.aol.com/supershuki/space/yourthinking

This is what I'm thinking:
http://members.aol.com/supershuki/space/mythinking

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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Thu Jan 12, 2006 10:21 pm
SuperShuki wrote:
If something in orbit gets pushed closer to the sun, in relation to a line drawn from the sun to the object, the gravity will increase. The additional pull of the sun on the object will be equalled out by decrease in velocity need to stay in a lower orbit- but the object will pull on the sun with greater force. Therefore, ipso facto, sum total, in the end and at the end of the matter, the object will spiral into the sun. Heavier objects fall faster than lighter ones.
8)


Well well well, let's get this straight (and I feel I'll live to rue this moment) :?
First the object is moving around the sun in a stable orbit. It has a (negtive) potential energy that is:
Epot = m(object) * M(sun) * G(gravity constant) / r (r being the magnitude of the sun-object vector)

And it has a (postive) kinetic energy that is:
Ekin = 1/2 m(object) * v^2 (v being the orbital velocity)

Remark: In any stable orbit, Ekin<Epot is necessary, because the total orbital energy of the object is always negative!

Now we unkindly apply an "external" force (indeed, any force) to the object, forcing it lower without changing its velocity (That is a complicated trick to do in space, but just the same). Now the potential energy is smaller, and the object has "not enough" kinetic energy to maintain its orbital parameters, so it will enter a stable orbit with a shorter period. Remember: Objects in lower orbits generally move faster, so what we have done is change the orbit in two ways. The new semimajor axis will be even shorter than the difference in altitude between "before" and "after", but it will still be a stable orbit. And this being a two-body problem of motion, the sun will, of course, move accordingly, but the orbit will still be stable. Conservation of kinetic energy says it must be. But what we have done is, we have simply changed the energy and the angular momentum of the orbit. It will NOT go spiralling anywhere.

Now, there are two ways objects would spiral into the sun. :idea: The first is, if an object from outer space passes into the solar gravity influence with almost but not quite enough energy to enter a stable orbit. Then it will enter a short spiral into the sun. This happens to galaxies near black holes, but should be very rare with our sun. The second happens to planets over the eons - and I really mean many, many billions of years. They will be slowed down by friction with the solar wind, and by their own and their sun's tidal motion which receives its energy out of the planet/sun interaction. But both of these effects will hardly be noticeable by the time the sun blows up in a nova, so forget about them.

And finally: No object spirals outward from the sun. The only way it goes out is if it reaches solar escape velocity like Pioneer 11 did, and then it goes out in a long drawn-out hyperbola or parabola.

Hope this was clear 8)
Max

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Post Re: I'm faaaaaaaaaaaaaaaaaaaaaaaaaaaaalling! Ahhhhhhhhhhhhhh   Posted on: Thu Jan 12, 2006 10:43 pm
Max Lange wrote:
Now we unkindly apply an "external" force (indeed, any force) to the object, forcing it lower without changing its velocity


Here we seperate. When you force the object lower, the [angular] velocity increases, because it's falling faster!

Think of it like two magnets. The potential energy is different at different distances/altitudes.

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