Hello, This problem has probably been done before in different guises but I am struggling, and hoping for help. I am struggling to understand a phenomena which I am assuming is one and the same: Equatorial Bulge of the Earth Flat Plane in which the Planets rotate Protoplanetary disks are flat Disks around planets eg Saturn I was reading something about the Tides, and the High Tides on Far and Near-side of the Earth and got that, but then started to think about the Earth's own equatorial bulge and started to look for similar phenomena that might explain it, but no I am still stuck. In each of the examples we've got rotation. And I am constantly thinking about sedimentation in a centrifuge whereby the particles with the greater mass are "thrown" outwards. It does appear quite intuitive that if you rotate a deformable body it sill stretch out perpendicular to the axis of rotation like whirling pizza dough, but rather than keep looking for analogies, what's the physics behind this? I've been trying to find out online and come across a few explanations which I semi-understand. The Earth and the equatorial bulge is perhaps the easiest to have a go at, and it was my original problem. I have seen this argument and it does make some sense. I am repeating it to see if I can make more sense of it, and to see what other people think of it. What's going on at the equator that's different to the poles? The rotational velocity is at its maximum here. Matter here is being accelerated through the max circumference in a constant time, and this acceleration is provided by the Earth's gravity And therefore the gravitational force at the equator is reduced by the centripetal acceleration meaning matter is less tightly held by the Earth's centre deforming the sphere. I know that the bulge itself increases the Earth radius, and therefore reduces g, but I want to know what caused the bulge in the first place. Following this through, there must be a theoretical maximum rotation rate above which matter would just fly into space? Is this explanation OK? Does it also cover the accretion disk, and centrifuge. I don't think it does. I looked online and got a bit dazzled by rotational frames of reference and fictional forces so I am hoping someone can help me understand. I've probably combined a few phenomena that are unrelated. As I was unable to understand one, I looked for something similar and failed to grasp the whole lot! Hoping you guys can help. I've spent some time trying to figure this out and found an argument which makes some sense to me, but is it right? And does it explain the other phenomena?