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Some baryons families exhibit a relation between the spin and mass, where the spin scales as the mass squared  J \propto M^2 . 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  c . Suppose that this rod has mass density per unit length  \mu and length  l , so its mass is  m = l \mu . The angular velocity is given by  \omega = c/l . The energy of the string, even when its spinning, is proportional to the mass  e \approx m c^2 . The angular momentum is given by

 J \propto m \omega^2 l \approx \frac{m^2 c}{\mu} \propto m^2

Similar ideas are used in string theory to represent particles as modes in a vibrating string.