ABSTRACT
By Newton's law the value of acceleration is proportional to a force F having effect on the mass point, so the trace y of a mass point is more curved if the value of F is greater. When the mass point moves on y with a constant value of velocity Ivj = dsldt = const, the vector of acceleration is collinear to the principal normal of y and its value is equal to kv2, where k is the curvature of y. For example, a particle with electric charge moves in a similar way in a magnetic field.
