Euler's equations (rigid body dynamics)

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In classical mechanics, Euler's rotation equations are a vectorial quasilinear first-order ordinary differential equation describing the rotation of a rigid body, using a rotating reference frame with angular velocity ω whose axes are fixed to the body. They are named in honour of Leonhard Euler. Their general vector form is

${\displaystyle \mathbf {I} {\dot {\boldsymbol {\omega }}}+{\boldsymbol {\omega }}\times \left(\mathbf {I} {\boldsymbol {\omega }}\right)=\mathbf {M} .}$

where M is the applied torques and I is the inertia matrix. The vector ${\displaystyle {\dot {\boldsymbol {\omega }}}}$ is the angular acceleration. Again, note that all quantities are defined in the rotating reference frame.

In orthogonal principal axes of inertia coordinates the equations become

${\displaystyle {\begin{aligned}I_{1}\,{\dot {\omega }}_{1}+(I_{3}-I_{2})\,\omega _{2}\,\omega _{3}&=M_{1}\\I_{2}\,{\dot {\omega }}_{2}+(I_{1}-I_{3})\,\omega _{3}\,\omega _{1}&=M_{2}\\I_{3}\,{\dot {\omega }}_{3}+(I_{2}-I_{1})\,\omega _{1}\,\omega _{2}&=M_{3}\end{aligned}}}$

where M_k are the components of the applied torques, I_k are the principal moments of inertia and ω_k are the components of the angular velocity.

In the absence of applied torques, one obtains the Euler top. When the torques are due to gravity, there are special cases when the motion of the top is integrable.