D'Alembert's principle

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D'Alembert's principle, also known as the Lagrange–d'Alembert principle, is a statement of the fundamental classical laws of motion. It is named after its discoverer, the French physicist and mathematician Jean le Rond d'Alembert, and Italian-French mathematician Joseph Louis Lagrange. D'Alembert's principle generalizes the principle of virtual work from static to dynamical systems by introducing forces of inertia which, when added to the applied forces in a system, result in dynamic equilibrium.^[1][2]

D'Alembert's principle can be applied in cases of kinematic constraints that depend on velocities.^[1]: 92 The principle does not apply for irreversible displacements, such as sliding friction, and more general specification of the irreversibility is required.^[3][4]