1. The problem statement, all variables and given/known data A cylinder of mass M and radius R rolls (without slipping) down an inclined plane whose incline angle with the horizontal is theta. Determine the acceleration of the cylinder's center of mass and the minimum coefficient of friction that will allow the cylinder to roll. 2. Relevant equations Sigma Torque = moment of inertia * angular acceleration F = ma 3. The attempt at a solution So I am trying to understand this problem and theory, and I am left wondering the following: Why is it that we can write F = ma equations using the same forces that are used in rotational motion? Mgsin(theta) - Ff = ma? Why do they say that the "static friction" supplies the torque needed to allow the cylinder roll smoothly? Why do they take the torque around the contact point to solve for acceleration using the moment of inertia (3*M*R^2)/2 instead of the regular MR^2/2? Why do they say that the gravitational force Mgsin(theta) is the only one causing the torque when they start doing the math, but say earlier that "static friction supplies the torque that allows the cylinder to roll smoothly? I have a physics test tomorrow and am frantically trying to understand these points. Any help is greatly appreciated. Thanks!