Hello, I'm trying to understand circular motion more intimately. Let's say I have a 1.8 m long piece of twine that I attach to my ceiling and attach a rock with a mass of 650 g from the hanging end. Let's say (with my superhuman coordination) I manage to get the rock spinning in a perfectly horizontal circle (IE it doesn't move up or down in the z-axis at all) at a constant speed. If I know the angle the twine makes with the ceiling, is there a way to calculate the speed the rock is going around the circle at? Here are my initial thoughts. Once the motion has started and the rock is in its perfect circle at its constant velocity, let's say it makes a constant angle theta with the ceiling. Doing a little trig, the radius of the circle the rock is travelling in would be equal to 1.8sin(180 - theta) m. If we ignore drag and other neg. forces, then three forces are acting on the rock: gravity, tension, and a centripetal force. It is at this point that my whole body starts shaking and I generally pass out. In this ideal situation, the angle the string makes with the ceiling would be a function of the velocity the rock is travelling around the circle in and therefore the velocity the rock is travelling around the circle in would be a function of the angle. I have come up with two formulas for the rock's velocity, but in both mass disappears so they obviously can't be right. I would appreciate any help - or at least perhaps a site covering uniform circular motion a bit better than the two pages my textbook gives it. Thank you!