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?(adsbygoogle = window.adsbygoogle || []).push({});

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!

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Uniform circular motion; radial and lateral components?

**Physics Forums | Science Articles, Homework Help, Discussion**