and . Note that is being opposed and so rotation around this axis is stable for the object. Similar reasoning gives that rotation around axis with moment of inertia is also stable. Unstable rotation around the second principal axis Now apply the same analysis to axis with moment of inertia This time is very small. Therefore, the time dependence of may be neglected. Now, differentiating equation (1) and substituting from equation (3), Note that is not opposed (and therefore will grow) and so rotation around the second axis is unstable. Therefore, even a small disturbance along other axes causes the object to 'flip'. See also References External links on Mir International Space Station Louis Poinsot, Théorie nouvelle de la rotation des corps, Paris, Bachelier, 1834, 170 p. : historically, the first mathematical description of this effect. - intuitive video explanation by Matt Parker Classical mechanics Physics theorems Juggling