Right, so I have a mechanics module tomorrow morning, and I'm almost there, the only thing stumping me is the centre of mass of a uniform semicircular lamina. I have the formula for a sector of a circle, which is 2r sin(angle) sin (angle) (r is radius) Now when it's a semicircle then the angle would be ∏ radians, but sin(∏) is 0 therefore this formula isn't going to work. Am I missing something here? I did google this and the answer I saw is 4r 3p Yet nowhere I saw this did they say what p was. Is it short for pi? Thanks for any help, this is getting me stressed out!