Recent content by davicle

I can see why a point mass inside a sphere has no net gravitational attraction from any mass of the sphere "outside" that point, and is only acted on by that mass of the sphere inside. But my own doodlings have shown that this certainly does not happen with a disc. What does happen is that the...

Thanks very much for this. The calculus involved in dealing with a graded density circular disc must be complicated but I would like to see it and hopefully understand it. Could you give me a link to a paper where the derivation is explained step by step?

Thanks for this - it was most helpful. But on reading this it raised more questions than answers. Newton's equation strictly applies to two point masses M and m separated by a distance d, which in theory is accurately known. But when one of the masses M is diffuse e.g. a galaxy, you run into a...

I am probably asking a question which has been asked before, but I have only just joined the forum. I have looked at sketch curves showing the actual and "expected" galaxy rotation curves. My question is - on what basis do astronomers expect the curve that they say they expect. And what...