4.1 Like and Unlike Parallel Forces
If parallel forces are acting in the same direction, they are called like parallel forces. If their directions are opposite to one another, they are called unlike parallel forces.
Three forces F₁, F₂, and F₃ acting on a rigid body at different points are shown in Fig. 4.1. Here, forces F₁ and F₂ are like parallel forces, but F₂ and F₃ are unlike parallel forces.