[Physics] For a rolling object, is the tangential velocity the same as the velocity of the center of mass

rotationrotational-kinematics

For example, a solid disk rolling down a hill would include both rotational and linear kinetic energy. For the rotational kinetic energy ($\frac{1}{2}I\omega^2$) the angular velocity becomes $v/r$ but what kind of velocity is it? I always assumed it was tangential. In the case of the disk rolling down the hill, would the $v_{tan}$ be the same as the $v_{cm}$?

If so, why? Seems kind of intuitive but I don't know how to prove it.

Best Answer

Rolling of a circular body, on a flat surface, and without sliding results in $v_\text{tan}=v_\text{cm}$ where $v_\text{tan}=ωr$ is the tangential speed of any point on the rim of the body in the center-of-mass frame of reference.

This is understood by studying the motion in the c.m. frame: there, the flat surface has velocity $v_\text{cm}$ (backwards). The no-sliding condition implies it to be equal to the rim tangential speed.

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