Now that we have extended objects that can exhibit two different types of motion, translational motion and rotational motion, how we have previously calculated the kinetic energy of an object, `\frac{1}{2}mv^2`, can no longer be sufficient to keep track of the total energy an object has due to its motion.  Because we have two types of motion, we need two forms of kinetic energy.  Though we won’t always have objects that only rotate about their center of mass, an axis through the center of mass does provide a useful framework for breaking up the kinetic energy of an object into the two pieces we need, one for the motion of the object’s center of mass and the other for the motion of the object about its center of mass.  As a result, we can calculate the translational and rotational kinetic energies of an extended object to keep track of its total kinetic energy.