This paper describes a secondary school experience which is intended to help students to think profoundly about some energy-related concepts. It is quite different to other experiences of mechanics because the focus is not on the quantitative calculation of energy conservation but on the qualitative understanding of energy degradation. We first present an experience where students study the friction produced between a wheel and a piece of copper foil that acts as a brake pad. Then, we present an educational approach specially designed for the experience. Some visual representations have also been specially designed to support the learning process. (Contains 7 figures.)