Mechanical similarity

In classical mechanics, a branch overlapping in physics and applied mathematics, mechanical similarity occurs when the potential energy is a homogeneous function of the positions of the particles, with the result that the trajectories of the particles in the system are geometrically similar paths, differing in size but retaining shape.
Consider a system of any number of particles and assume that the interaction energy between any pair of particles has the form 
where "r" is the distance between the two particles. In such a case the solutions to the equations of motion are a series of geometrically similar paths, and the times of motion "t" at corresponding points on the paths are related to the linear size "l" of the path by