What is D'Alembert's Principle? For a system of mass of particles, the sum of the difference of the force acting on the system and the time derivatives of the momenta is zero when projected onto any virtual displacement.

Applications of D'Alembert's Principle\n\n D'Alembert's principle is based on the virtual work principle as well as inertial forces. The following are examples of D'Alembert's principle in action: Free fall of a mass under gravity. Theorem of Parallel axis.