Two similar experiments on conservation of energy and transformation of mechanical into electrical energy are presented. Both can be used in classes, as they offer numerous possibilities for discussion with students and are simple to perform. Results are presented and are precise within 20% for the version of the experiment where measured values are available over the complete time of the experiment, and within a few percent for the simpler implementation of the same experiment where only final results are shown. (Contains 1 table and 8 figures.)