Teaching envelopes in secondary school

Borislav Lazarov

The paper presents an educational module, in the spirit of inquiry based method, which is concerned with the case of some simple envelopes. The inclusion of dynamic geometry system applets in presenting the topic allows the shape of the envelope of one-parameter family of curves to be established by examining dynamic constructions. Starting with an example for the Euler formula, further motivation of introduction of envelopes belongs to the field of kinematics. Two main problems are under consideration: the misty sprinkler and the wet wheel. The introductory part of the kinematics problems does not go out of the common school practice.