Some baryons families exhibit a relation between the spin and mass, where the spin scales as the mass squared . In what follow we present a mechanical system that exhibits a similar relation between its mass and angular momentum. Let us consider rigid rod rotating in such a way that its ends are moving at the speed of light . Suppose that this rod has mass density per unit length and length , so its mass is . The angular velocity is given by . The energy of the string, even when its spinning, is proportional to the mass . The angular momentum is given by
Similar ideas are used in string theory to represent particles as modes in a vibrating string.