I have a shaft within a pipe, all horizontal. Shaft diameter is 2.875" and pipe inner diameter is 5". Shaft and pipe length is 650 ft. Shaft weight is 2500 lb. I need to determine the torque needed to begin rotating the shaft. The coefficient of static friction between the shaft and the pipe is 0.3 T = I * a T = F * Rs Fr = Cf * Fn T = torque I = moment of inertia a = angular acceleration F = force Fr = force of friction Rs = radius of shaft = 2.875/2/12 = 1.4375/12 = 0.12 ft Rp = radius of pipe = 5/2/12 = 2.5/12 = 0.208 ft Cf = coefficient of friction = 0.3 Fn = force normal to shaft = 2500 lbf L = length of shaft and pipe = 650 ft What I have so far is: Fr = 0.3 * 2500 = 750 lbf T = 750 * 0.12 = 90 ft-lbf So 90 ft-lb is what needs to be overcome according to this. This is bothering me because it does not take into account the inertia equation or the surface area of contact between the shaft and pipe. Wouldn't a greater surface area result in a greater amount of friction acting against motion. What do I use for angular acceleration in the inertia equation? Can someone please get me on the right track here?