Original: The continuum concept ignores the fact that matter is made of atoms , is not continuous , and that it commonly has some sort of heterogeneous microstructure , allowing the approximation of physical quantities , such as energy and momentum , at the infinitesimal limit .
Simplified: The fact that all matter is made of atoms and that it commonly has some sort of heterogeneous microstructure is ignored in the simplifying approximation used in continuum mechanics .