  This article describes use of Mathcad mathematical package to solve problem
of the motion of two, three and four material points under the influence of
gravitational forces on the planar motion and in three-dimensional space. The
limits of accuracy of numerical methods for solving ordinary differential
equations are discussed. Usual concept of Kepler hours with uneven movement
arrows illustrates Kepler's second law. Mathcad animation tools are used to
illustrate solutions and links with animations are provided.
