too-open-minded Posted June 19, 2012 Share Posted June 19, 2012 When i ask this question many of you will envision the force of gravity, though this is not what i am asking. If everything with mass can exert gravitational force when confronted to another body with mass, is their a proportion for mass to gravitational field? example - for every G of mass their is an F to its gravitational field From what i understand this is heresy because gravity will always have an affect, no matter how far away it is from an object. I'm uneducated in physics having never taken a class although i will in the fall and have taught myself some basics. I'm really asking why this is impossible, not if theirs anything to it. How do we know gravitational fields are infinite? Link to comment Share on other sites More sharing options...
swansont Posted June 19, 2012 Share Posted June 19, 2012 Gravitational fields follow a 1/r^2 pattern: F = GMm/r^2, and this means there is no limit to the range. Furthermore, this pattern is required for closed orbits to exist. It's pretty well tested over scales the size of our solar system. The rest is extrapolation, based on the testing we have done. (We also know that there are some modifications to Newton's model for very large fields, which is why we have General Relativity, but this reduces to the Newtonian formula when the fields aren't large. Still infinite in range) 1 Link to comment Share on other sites More sharing options...
too-open-minded Posted June 23, 2012 Author Share Posted June 23, 2012 Thankyou very much swansont you are the only person to have answered this question for me. Call me crazy, mind you I have never taken a physics class, but I think it theoretically eventually can reach zero. So maybe when i do start college in the fall i will eventually see why I'm wrong. I most likely am wrong, for i have no grounds to say otherwise and have no idea what those equations you showed me means. I just don't think something physical can infinite. Link to comment Share on other sites More sharing options...
pmb Posted June 25, 2012 Share Posted June 25, 2012 (edited) Thankyou very much swansont you are the only person to have answered this question for me. Call me crazy, mind you I have never taken a physics class, but I think it theoretically eventually can reach zero. So maybe when i do start college in the fall i will eventually see why I'm wrong. I most likely am wrong, for i have no grounds to say otherwise and have no idea what those equations you showed me means. I just don't think something physical can infinite. The meaning of F = GMm/r^2 is as follows. First off his "G" is not what you used in your first post. It's a constant of proportionality. The M is the mass of a point sized object and m is also the mass of a point sized object. The r is the distance between the two point particles. In our case we can treat the Eath as a partilce because the gravitational field around the Earth is as if its due to a point sized object,so long as you stay outside the body of the Earth. Let m be the mass of your body. Compared to the size of the Earth your body can be considered a point object. The force between you and the Earth is then given by F = GMm/r^2. The same thing holds between any two objects which are far enough from each other so that the shape of the body doesn't come into play. E.g. if you and a truck are 50 feet a part then the force between the truck anbd you are F = GMm/r^2 where now M = mass of truck and m = mass of your body. Edited June 25, 2012 by pmb Link to comment Share on other sites More sharing options...
too-open-minded Posted June 28, 2012 Author Share Posted June 28, 2012 I'm only wondering if an equation can be made to find the strength of a gravitational feild. The mass to gravitational field exerted proprtion, shouldnt their be one? Link to comment Share on other sites More sharing options...
Spyman Posted June 28, 2012 Share Posted June 28, 2012 The answer is Yes, both swansont and pmb has already showed you the equation. The force of gravity is proportional to mass and distance, greater mass gives greater force and greater distance gives weaker force. Link to comment Share on other sites More sharing options...
too-open-minded Posted June 28, 2012 Author Share Posted June 28, 2012 Yes i understand gravity is a force between 2 objects but their has to be a gravitational field prior to the force being exerted. Can you measure an objects gravitational field? not the gravitational force. I'm sorry if i am just misunderstanding and not reading the equations right, it has to be very aggravating repetitivley answering this question for me. Can you explain with words how to find an objects gravitational field? you can say F=MA for me to understand how to measure force but i understand it better when stated; force equals the space an object takes up multiplied by its speed/rate of speed and distance from zero. Link to comment Share on other sites More sharing options...
swansont Posted June 28, 2012 Share Posted June 28, 2012 A field is a representation of what force an object would feel, which you get by diving by the value of whatever "charge" you'd place there; in electrostatics it's F/q, i.e. you divide by the electrostatic charge. For gravity the field is the force per unit mass, so the field is given by GM/r^2, where M is the mass of the object creating the field. An object of mass m placed in that field will experience an attractive force of magnitude GMm/r^2. Because F=ma, this field is just the acceleration. (though I've only given equations for the magnitude; you'd put in a negative sign to account for the direction) Link to comment Share on other sites More sharing options...
Spyman Posted June 28, 2012 Share Posted June 28, 2012 I think too-open-minded are asking about a boundary of the gravitational field and not the strength of it at different positions inside it. In the Newtonian model objects gravitational field acts instantly even at infinite distance and as such reaches everywhere inside the Universe. In the theory of Relativity the gravitational field reaches out with the speed of light from objects and has a boundary determined by c and time. But in neither of the two models does more massive object have larger gravitational fields, that reaches further or faster, than less massive ones. If you are inside an objects 'visual' range then you are inside its gravitational field and the gravity measured emenates from the location where the object you see appears to be, with the strength it had when it looked like it shows. Link to comment Share on other sites More sharing options...
pmb Posted June 28, 2012 Share Posted June 28, 2012 I'm only wondering if an equation can be made to find the strength of a gravitational feild. The mass to gravitational field exerted proprtion, shouldnt their be one? I'm sorry but I don't understand your question. swansont and myself have already show you the equation that you're asking about. It's F = GMm/r^2. Since we already posted it I don't know what you're now looking for. Can you clarify this for me? Link to comment Share on other sites More sharing options...
too-open-minded Posted June 30, 2012 Author Share Posted June 30, 2012 Well swansont definitely cleared that up a bit for me but I think my question will be better asked after i have taken a few physics classes and have some general knowledge of the subject. like D.Dennet said - " What you can imagine, depends on what you know " Spyman is right though as to what I am wondering. After i have taken some classes I'm guessing I will be proven wrong but untill then I think that gravity is infinite like current physics says ( I don't like it but stand nowhere to think otherwise. ) If their was one then theoretically gravity itself is not infinite and something else has to account for why their is always an attraction. Kind of like photons having mass but only because they are moving. Anyways my question has been answered, their is no mass to gravity proportion and no reason to believe their should be. I don't want to agitate any more mods as this topic should now belong in speculations. Thank you all for your help and input. Link to comment Share on other sites More sharing options...
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