Kinetics of a Particle

(ii) D' Alembert's principle:

Newton's second law is

F = ma

We can write it

F + (-ma) =0

We know that F is the resultant of external forces applied on the particle.

Considerring (-ma) as a force, we can say that the body is in equilibrium under the action of external forces and force (-ma). This fictitious force is known as inertial force, and the artificial state of equilibrium created is known as dynamic equilibrium. The apparent transformation of a problem in dynamics to one in statics has become known as D' Alembert's principle. D' Alembert's published his work in his "Traite de Dynamique" in 1743.