D'Alembert's principle can be rewritten in terms of the Lagrangian L=T-V of the system as a generalized version of Hamilton's principle as follows, δ δ ∫ ∫ t 1 t 2 L ( r , r ˙ ˙ , t ) d t + ∑ ∑ i ∫ ∫ t 1 t 2 F i ⋅ ⋅ δ δ r i d t = 0 , where: