Rolling, Torque, and Angular Momentum (Physics Question)

[vladittude0583]

Hey guys, I am having a little hard time understanding a concept dealing with translational and rotational motion. For instance, if we have a solid sphere rigid body rolling down on an incline, we have both translation kinetic energy with regards to the center of mass and that of rotational kinetic energy associated with the particles of the sphere. Anyhow, my textbook mentions that it is static friction involved in ensuring this rigid body rolls "smoothly" down the incline without slipping. My question is, why is it static friction? I thought static friction needs to be overcome for a body to start moving? Can someone clarify this? Thanks.