Thus it is the reaction force on link 1 which is centrifugal, not the force on link 2. Of course, it is this reaction force that your hand (link 1) feels, and this gives rise to the popular conception of something pulling centrifugally on the rotating weight. Now let us look at this through d'Alembert's eyes. Figure 10-lOc shows another set of free-body diagrams done according to the principle of d'Alembert. Here we show a negative ma inertia force applied to the mass on link 2. The force at the pin from d'Alembert's equation is: