High school physics students are taught so-called Newtonian mechanics, but cannot solve the simple problem of a ball rolling down an inclined plane. Rigid bodies are outside the purview of Newtonian mechanics, as Newton himself seems to have admitted in The Principia. However, the application of D'Alembert's Principle yields a solution to this simple problem. The problem becomes particularly simple when worked out for a thin cylinder or ring rolling down an inclined plane. Should high school students be introduced to D'Alembert's Principle?