Phanerothyme Posted February 27, 2012 Share Posted February 27, 2012 Gravity doesn't have a speed, it causes acceleration https://en.wikipedia.org/wiki/Gravitational_acceleration But it's effect are instantaneous at any distance, surely? If it propagated at any measurable speed, the rate of change in the gravitational field on the surface of the earth, as the moon passed overhead, would have revealed this to be the case? Link to comment Share on other sites More sharing options...
ElasticMan Posted February 27, 2012 Share Posted February 27, 2012 Sorry about that the thread title misled me into thinking you wanted facts or information rather than speculation., my bad. Edit..............cut Link to comment Share on other sites More sharing options...
Cyclone Posted February 27, 2012 Share Posted February 27, 2012 Gravity has no speed, its a constant. However a falling body under the effect of gravity accelerates at a speed of 32 feet per second per second. It doesn't matter how big or heavy it is, it will always speed up at that rate in clear air. Newton's law. I think you might have misunderstood the question, which has been answered as well as we are able at the moment. It's probably the speed of light, but given that we don't yet know how gravity is transmitted, we don't know for sure. If we could make matter appear/disappear, then we'd be able to test it experimentally quite easily, but we can't. Link to comment Share on other sites More sharing options...
llamatron Posted February 27, 2012 Share Posted February 27, 2012 surely it is like asking the speed of the acceleration of a car, the question doesn't make sense. Or is the question "how fast does gravity act?" Link to comment Share on other sites More sharing options...
truman Posted February 27, 2012 Share Posted February 27, 2012 I think you might have misunderstood the question, which has been answered as well as we are able at the moment. It's probably the speed of light, but given that we don't yet know how gravity is transmitted, we don't know for sure. If we could make matter appear/disappear, then we'd be able to test it experimentally quite easily, but we can't. If gravity wasn't near instaneous ( ie faster then light) then wouldn't this have an effect on planets' orbits? If this were the case then the earth would be being affected by a force between it and the sun acting on their position relative to each other 8 minuites earlier..would this still allow the regular orbit we have? Link to comment Share on other sites More sharing options...
Petminder Posted February 27, 2012 Share Posted February 27, 2012 I always thought gravity acted in a similar way to a magnetic field which propagates out away from the source at the speed of light. Link to comment Share on other sites More sharing options...
Jabberwocky Posted February 27, 2012 Author Share Posted February 27, 2012 Ok I bowed to pressure and Googled it. "How fast is gravity?" I asked. It brought me here, to this thread.... heh Link to comment Share on other sites More sharing options...
Cyclone Posted February 27, 2012 Share Posted February 27, 2012 If gravity wasn't near instaneous ( ie faster then light) then wouldn't this have an effect on planets' orbits? If this were the case then the earth would be being affected by a force between it and the sun acting on their position relative to each other 8 minuites earlier..would this still allow the regular orbit we have? I think it would, but my A level physics is too far in the past to quickly work it out. To reverse your question though, since the light from the sun does take about 8 minutes to reach us, and if gravity were instantaneous, wouldn't we appear to be orbiting a patch of space a little bit to the side of where we see the sun??? Link to comment Share on other sites More sharing options...
Phanerothyme Posted February 27, 2012 Share Posted February 27, 2012 I think you might have misunderstood the question, which has been answered as well as we are able at the moment. It's probably the speed of light, but given that we don't yet know how gravity is transmitted, we don't know for sure. If it was as slow as that, we'd have measured it by now, surely? I think that, in one way or another, gravity is propagated through something analogous to 'entanglement' - thus is instantaneous. Link to comment Share on other sites More sharing options...
Cyclone Posted February 27, 2012 Share Posted February 27, 2012 surely it is like asking the speed of the acceleration of a car, the question doesn't make sense. Or is the question "how fast does gravity act?" The question makes perfect sense, does the force of gravity propagate instantaneously, or with a velocity. The force is what creates the acceleration, not the act of acceleration itself. http://en.wikipedia.org/wiki/Gravitational_wave The model of relativity predicts that gravity has a propagation speed, unlike the newtonian model which assumes instantaneous transmission. Link to comment Share on other sites More sharing options...
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