The momentum, angular momentum, kinetic energy, and the inertia tensor of a rigid solid are studied. The dynamic Euler equations are derived from the angular impulse-momentum principle. Transformations of the force systems applied to a rigid solid are investigated, the equations of statics are considered as a particular case of the dynamic equations. The Euler and Lagrange cases of rotation of a heavy rigid solid around a fixed point are presented. The elementary theory of gyroscopes is built on the basis of the results obtained for the pseudoregular precession of a heavy gyroscope. A new special form of differential equations for motion of a system of rigid solids which is comfortable for using numerical methods is given.