ga * b.x)
        >>> P = Point('P')
        >>> P.set_vel(N, v * N.x)
        >>> I = outer (b.x, b.x)
        >>> inertia_tuple = (I, P)
        >>> B = RigidBody('B', P, b, M, inertia_tuple)
        >>> B.kinetic_energy(N)
        M*v**2/2 + omega**2/2

        é