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quote:Originally posted by DoctorBeaveranother_someone - I appreciate what you're saying, but I was thinking of a construction of many ball bearings pressed together. You wouldn't then be able to get between them. The gravitational attraction is measured as if it all emanated from a single point at the centre of mass.However, in your example of being between 2 balls, your mass would have to be added to the system. If the balls were of equal weight and equidistant from you, then the centre of mass of the system would be somewhere inside you.
quote:Originally posted by DoctorBeaverBut it has been shown that the gravitational pull of the earth is fractionally less at the top of a mountain than it is at ground level. That shows that gravity cannot be coming from the surface.
quote:Thus gravity is proportional to the mass of each object, but has an inverse square relationship with the distance between the centres of each mass.Strictly speaking, this law applies only to point-like objects. If the objects have spatial extent, the force has to be calculated by integrating the force (in vector form, see below) over the extents of the two bodies. It can be shown that for an object with a spherically-symmetric distribution of mass, the integral gives the same gravitational attraction on masses outside it as if the object were a point mass.
quote:This is what is meant by having a flat universe
quote:Originally posted by DoctorBeaverIan - thanks for that. So I can blame those buggers who over-simplified it in the 1st place! grrrrrrrr quote:This is what is meant by having a flat universeI thought that meant the geometry of the universe was basically Euclidean rather than Riemannian.
quote:But if there is no detectable gravity, then would we not in fact have a Euclidean geometry, since there would not be any gravity to curve space?
quote:Originally posted by Solvay_1927Eth,So the question is, how can the total gravitational attraction of the sphere be proportional to the total number of ball bearings in it (1 million)? How can the ball bearings on the inside contribute to the total attraction, given that the inner ones can’t “see out” to interact with the external world? Why isn’t the total gravitational attraction of the sphere proportional to the number of ball bearings (c.50,000) on the surface instead?
quote:Or is this just a stupid question that betrays my complete ignorance of physics?[:I]
quote:--------------------------------------------------------------------------------Or is this just a stupid question that betrays my complete ignorance of physics?--------------------------------------------------------------------------------Probably ...
quote:Originally posted by Solvay_1927OK, so I know it was a really stupid question. But I suppose what I'm getting at is why can't you block gravity? How can the gravitational influence (on me, say) of each ball bearing not be affected in any way by the presence of other ball bearings which are in the way?None of the other forces work like that, do they? (Magnetism/electromagnetism - or even the weak & strong forces?) And no particles can bypass all matter? (OK, neutrinos come close in that most of them can pass through the entire earth without intereacting with anything - but they don't all get through.)Don't worry, I'm not expecting anyone to have an answer. I'm just thinking aloud.
quote:Originally posted by Soul SurferAndrew what you are saying is not true and I doubt that any effects on people with MS have anything to do with gravity.Learn, create, test and tellevolution rules in all thingsGod says so!
quote:So the question is, how can the total gravitational attraction of the sphere be proportional to the total number of ball bearings in it (1 million)? How can the ball bearings on the inside contribute to the total attraction, given that the inner ones can’t “see out” to interact with the external world? Why isn’t the total gravitational attraction of the sphere proportional to the number of ball bearings (c.50,000) on the surface instead?
quote:You must remember that the gravitational field near to an irregularly shaped object (like your three ball bearing model) IS irregular it is only at large distances where the difference between squares of the distance to the nearest part and the most remote part can be neglected that the centre of gravity simplification is valid. The sphere is a special case because of its symmetry and the gravitational field over the surface of a uniform sphere is constant and equal to the effect of having all the mass concentrated at the centre.
quote:Also looking at your original question there is some fundamental wrong thinking about quantum interactions when you talk about things "knowing" what to do,then exchanging particles this is not the way it is. The particle that is exchanged IS the knowledge that the other particle is near. This is best described aby two electrons colliding and bouncing off each other by coulomb repulsion the energy changes associated with the interaction are eplained in terms of the exchange of a photon between the two electrons.
quote:If gravity is mediated by particles, how do the particles "know" when to interact? I would have thought it reasonable to assume that the gravitating objects have to be exchanging and receiving gravitons ALL the time. Otherwise, what would cause them to "switch on" the exchange and suddenly start interacting? And is that any different to the idea of the continuous sending out of gravitons in all directions (and receiving back different gravitons from different sources in every direction)?
quote: Am I alone in thinking that all gravity comes from the past, that being the singularity at the begining of our universe.That while Time flows in one dirrection the attractive force of gravity acts as if it is trying to take us back in time.Tomorrow lies outside our universe without it there would be no tomorrow.by Mad Mark
quote: Nothing happens before the exchange of particles.
quote:If they were emitted and lost the electron would loose energy and in the absence of anything else that just cannot (and does not) happen so they must be reabsorbed witihn the time and space limits set by the uncertainty principle.
quote:Do dark matter and energy seem just silly to anyone else? It really seems to me there must be a simple explanation for the gaps between theory and observation. It seems far more likely there's a problem with the theory rather than there's a load of matter and energy that we can't see for some reason.