A covariant four-tensor rotation equation—for bi-dimensional composite body—, by generalising cross product to four-vectors, is obtained. From it, a relativistic angular impulse-angular momentum variation equation (Poinsot–Euler rotation equation) and its pseudo-work-rotational kinetic energy variation equation (Poinsot–Euler pseudo-work equation), are obtained for a body spinning—with constant angular momentum direction—by external torques. Two rotational processes are analysed by using this four-tensor formalism—completed by a four-vector fundamental equation (Newton’s second law and thermodynamics first law)—: a rotating body subjected to conservative and friction forces torque—a mechanical energy dissipation process—, and a device spinning by torque produced by chemical reactions—a mechanical energy production process.

通过将叉积推广到四向量，获得了用于二维复合体的协变四张量旋转方程。从中，得到一个相对论角冲量-角动量变化方程（Poinsot-Euler旋转方程）及其伪功-旋转动能变化方程（Poinsot-Euler伪功方程），用于一个具有恒定角的旋转体动量方向——通过外部扭矩。用这种四张量形式分析了两个旋转过程——由四向量基本方程（牛顿第二定律和热力学第一定律）完成——：旋转体受到保守和摩擦力扭矩——机械能耗散过程——，以及通过化学反应产生的扭矩旋转的装置——一种机械能产生过程。