harsh Posted August 14, 2004 Posted August 14, 2004 In a recent lecture i have heard that when we apply a force on the earth the earth also applies a equal and opposite force ..its is proved that there is acceleration of the earth in such cases ...well if its true why is the earth still in its orbit??... according to a few formulas P=f/a , therefore if the earth applies a force it should creat some pressure and space being vaccum the earth should be sucked up by it momentarly......how ever small the force may be eventully these small movements will result a shif of the earth out of its orbit and if that is true it would take a tagential part maybe into the sun.....
fuhrerkeebs Posted August 14, 2004 Posted August 14, 2004 I think you got your formulas wrong buddy. F=dP/dt, which works out to be F=ma.
swansont Posted August 14, 2004 Posted August 14, 2004 An object's macroscopic motion is dictated by the forces acting on it, not by the forces it exerts.
Severian Posted August 14, 2004 Posted August 14, 2004 I have always found it interesting that gravity is a 1/r2. If you sit down and work out the orbit equations 1/r2 is the only law which has stable orbits. 1/r or 1/r3 and no planets would form....they would either fall into the sun or float away into space.... Is this a coincidence or an anthropic principle?
LucidDreamer Posted August 14, 2004 Posted August 14, 2004 I have always found it interesting that gravity is a 1/r2. If you sit down and work out the orbit equations 1/r2 is the only law which has stable orbits. 1/r or 1/r3 and no planets would form....they would either fall into the sun or float away into space.... Is this a coincidence or an anthropic principle? Could planets obtain orbitals with a force of 1/r or 1/r3 by traveling faster or slower?
fuhrerkeebs Posted August 14, 2004 Posted August 14, 2004 No...1/r2 is known as the inverse square law. It's a Newtonian theory of gravitational force between two objects. It's the same everywhere in the universe, for every kind if speed, motion, blah blah blah. Actually, the force between two masses m1 and m2 is actually Gm1m2/r2, where G is the gravitational constant and r is the distance between the two masses.
LucidDreamer Posted August 14, 2004 Posted August 14, 2004 What I mean is in a different system where gravity was Gmm/r or Gmm/r^3 could orbitals be formed by changing the radiuses of the orbitals or speed of satellites, etc?
[Tycho?] Posted August 15, 2004 Posted August 15, 2004 What I mean is in a different system where gravity was Gmm/r or Gmm/r^3 could orbitals be formed by changing the radiuses of the orbitals or speed of satellites, etc? Yeah, you'd think it would... but then I havn't worked out the math, nor do I really know what I'm talking about. Carry on.
Severian Posted August 15, 2004 Posted August 15, 2004 No, they couldn't - that's what I was meaning. It is quite surprising I think, but we need the inverse square law in order to form planets. If we had Gmm/r or Gmm/r3 we would be screwed because there would be no stable orbits whatsoever.
[Tycho?] Posted August 15, 2004 Posted August 15, 2004 Yeah that is surprising. It is definately counter-intuitive, although that sure isn't saying much. Neat, however.
harsh Posted August 15, 2004 Author Posted August 15, 2004 I think you got your formulas wrong buddy. F=dP/dt, which works out to be F=ma. at the end of it all when a opposite force is applied the earth does accelerate , but we cannot see it due to the size of the earth... P=F/A = m*a/A....so there will be pressure created and it will be sucked into spce....you may say that these reaction take place all over the world and will get nullified ...but if u look closer the area of Asia , being the largest , most populated continent will have more of these force making the nullification process insignificent and the earth should be sucked up....if the force is very small as it is over here the earths orbit will gradully turn from eleptical to spiral shaped.....and if the force is extremly large then it would move out in tangential path and then.............................
fuhrerkeebs Posted August 15, 2004 Posted August 15, 2004 What is going to suck the earth up? The earth is already in space, how is something going to get sucked into what it is already in?
LucidDreamer Posted August 15, 2004 Posted August 15, 2004 In a recent lecture i have heard that when we apply a force on the earth the earth also applies a equal and opposite force ..its is proved that there is acceleration of the earth in such cases ...well if its true why is the earth still in its orbit??... according to a few formulas P=f/a , therefore if the earth applies a force it should creat some pressure and space being vaccum the earth should be sucked up by it momentarly......how ever small the force may be eventully these small movements will result a shif of the earth out of its orbit and if that is true it would take a tagential part maybe into the sun..... I'll give my very uneducated opinion on this one. First of all, I don't believe that the objects on the earth really cause a net force in any direction. Say you decided to jump up in the air in order to move the earth. By pushing down you are exerting a force down and the earth is exerting a force upward so you push the earth down a miniscule amount while you move upward a larger amount. While you’re in the air the earth is exerting its force of gravity on you so you return to where you jumped, but so does the earth. You exert a very miniscule force of gravity upward on the earth to the same degree that you moved it down when you jumped. Net result is that you both return to where you started. Also, I don't believe that the earth's orbit has always been exactly the same. Say a meteorite comes crashing into the earth and manages to pass through atmosphere and reach the Earth. This meteorite is only the size of a TV though so it exerts a very small force on the massive earth. The earth will change its orbit ever so slightly but its not enough to make any real difference. Satellites around the sun are fairly stable. If you exert a small force on them they will adjust their orbitals slightly but wont go flying into outerspace.
Martin Posted August 16, 2004 Posted August 16, 2004 I have always found it interesting that gravity is a 1/r2. If you sit down and work out the orbit equations 1/r2 is the only law which has stable orbits. 1/r or 1/r3 and no planets would form....they would either fall into the sun or float away into space.... Is this a coincidence or an anthropic principle? I find this interesting too. I suspect it is not coincidence or anthropic either' date=' but something else. [bTW No one else in this thread pointed out that you said [b']stable[/b] If gravity were 1/r3 then I think you could still have an exactly circular orbit, but it would not be stable and if something should accidentally come by and tug the planet slightly it would drift away. It can only stay orbiting if it keeps exactly in a circle and is never disturbed. Have you ever met a person like that?] Just a wild guess about the 1/r2 law. It seems to me to come from the fact of 3 spatial dimensions. Area increases with the square of distance. Illumination falls off with the square of distance. If only we could explain why there are 3 spatial dimensions! A mathematician (at Cambridge?) named Hendryk Pfeiffer has published some papers trying to say what is special about 3D. Someone else published something about that recently but I forget his name. If people can find a lot of things that are mathematically special about 3 dimensions (instead of 2 or 4 spatial dimensions) then perhaps they can get an idea about why Nature chose that number. Maybe we should have a thread where people can put links to research showing specialness of 3 spatial dimensions
harsh Posted August 16, 2004 Author Posted August 16, 2004 What is going to suck the earth up? The earth is already in space, how is something going to get sucked into what it is already in? Its like this when we have a ping pong ball and there is a area of vaccume the ping pong ball will move from a region of high pressure(atmosphere) into the vaccume, the same way once the force is created a small pressure is created on eart and the earth becomes the ping pong ball and it get sucked into a region of lower pressure space......well if u r confused with the reference think about the olden day method of passing obejcts in a office it used the same principle
fuhrerkeebs Posted August 16, 2004 Posted August 16, 2004 You didn't answer the questions, You just changed the word "space" to "vacuum"
harsh Posted August 16, 2004 Author Posted August 16, 2004 its like this if there was no gravity the atmosphere of earth would get sucked into space now when the force is applied by earth there is a pressure cretead on earth...and the earth being in object of higher pressure will move into space
fuhrerkeebs Posted August 16, 2004 Posted August 16, 2004 I get what your saying now...but for what you're describing (earth getting displaced because of the pressure) won't happen because your thinking of gravity pushing the atmosphere on earth, when really it's pulling it.
harsh Posted August 16, 2004 Author Posted August 16, 2004 what i am trying to expalin is very difficult for me to express...there are 2 sides of a coin same way 1 can say the earth is pulling me towards it and one can also say i am pulling the earth towards me.....i cant express it....anywyas i hav a another question what will happen or will be formed it u pass through a wire electrons and positrons??
fuhrerkeebs Posted August 16, 2004 Posted August 16, 2004 Yes, but your idea requires something to be pushing the atmosphere towards the earth...and that is not valid no matter how you look at it. And electrons and positrons can't technically be "passed" through a wire, what happens when you transmit electricity through wires is that the electrons on a wire are nudged off on one end when you put a new one on.
Thales Posted August 16, 2004 Posted August 16, 2004 if you evacuated the space and passed electrons and positrons at each other so they collided they would annihalate into a photon (and a gamma ray i think..)
swansont Posted August 16, 2004 Posted August 16, 2004 ...there are 2 sides of a coin same way 1 can say the earth is pulling me towards it and one can also say i am pulling the earth towards me..... That's a consequence of Newton's 3rd law. Action and reaction. But the earth's motion is only influenced by the force you exert on it, not the force it exerts on you. The fact that they are equal and opposite tells us momentum will be conserved in any interaction involving those two objects.
harsh Posted August 16, 2004 Author Posted August 16, 2004 not sure abt its coverting into photons...the -ve electron and + positron will get attracted to form this well bounded thing i guess and it will be like the formation a huge block to electron,positron thing i guess not sure....
fuhrerkeebs Posted August 16, 2004 Posted August 16, 2004 The positron and the electron are anti-particles of each other. When a particle and it's anti-particle collide it creates a photon. Simple stuff. No "huge blocks", no "well bounded things", just light.
harsh Posted August 16, 2004 Author Posted August 16, 2004 ohhh i see thanks for the info......so in this case mass is converted compeletly into energy..........
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