The Kovalevskaya Top is one of a brief list of known examples of integrable rigid body motion . It was discovered by Sofia Kovalevskaya

Sofia Kovalevskaya

Sofia Vasilyevna Kovalevskaya , was the first major Russian female mathematician, responsible for important original contributions to analysis, differential equations and mechanics, and the first woman appointed to a full professorship in Northern Europe.She was also one of the first females to...

 in 1888 and presented in her paper 'Sur Le Probleme De La Rotation D'Un Corps Solide Autour
D'Un Point Fixe' .

It is defined as a top

Top (mathematics)

In the context of a module M over a ring R, the top of M is the largest semisimple quotient module of M if it exists.For finite-dimensional k-algebras , if rad denotes the intersection of all proper maximal submodules of M , then the top of M is M/rad...

 in which two of the principal moments of inertia are twice that of the third and the center of mass

Center of mass

In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

is in the plane of the two equal moments of inertia.