Make Fluxion with the kinetic energy of body i

def T_i(v_vars: List[fl.Var], mass: np.ndarray, i: int):
    """Make Fluxion with the kinetic energy of body i"""
    # Check that the lengths are consistent
    assert len(v_vars) == 3 * len(mass)

    # Mass of the body i
    m = mass[i]
    
    # kineteic energy = 1/2 * mass * speed^2
    T = (0.5 * m) * flux_v2(v_vars, i)
    return T