Circular motion or rotational motion is present everywhere in space, from the circular motion of electrons in an atom to the rotation of the planet Earth around its axis. We describe the circular motion of a rigid body by equations called Euler's equations, named after Leonhard Euler who developed the dynamics of a rigid body in the 18th century. These equations describe stable or normal circular motions. During his stay in space, Russian astronaut Vladimir Alexandrovich Janibekov noticed instability in the rotation of the butterfly queen around one of the axes of rotation in the weightless state. This effect was later observed in many bodies that have three different moments of inertia, the phenomenon can be easily demonstrated using a tennis racket, and is therefore called the tennis racket theorem or Janibek's theorem. In the three-dimensional space, the motion of a rigid body implies the translation of the material points of the body and its rotation about a given axis. In Janibek's theorem, the translation does not appear, so we will theoretically process only the rotation of an angular body. The Janibek effect is theoretically not a new phenomenon, its physical manifestation, or more precisely the visual effect, looks very interesting and attractive. It is especially attractive to perform experiments in a weightless state, where the periodicity of the change in the direction of the axis of rotation can be seen very clearly. We have shown that every body that has three different moments of inertia has one axis that is unstable. By setting the rotation around the unstable axis, the body will periodically change the direction of rotation, ie it will additionally rotate around the other axis.