As one of the most important factors of Mechanical Engineering, it is important to note that when any rigid body is placed in space, those forces that are acting on the rigid body, may either be concurrent or non-concurrent.
In case concurrent forces are acting on it, resulting equation is ƩFx = 0, ƩFy = 0 and ƩFz = 0
In case, non-concurrent forces are acting on it, resulting value is ƩFx = 0, ƩFy = 0 and ƩFz = 0
While, it is also taken as: ƩMxy = 0, ƩNxz = 0 and ƩMyz = 0
In this case, force has 3 equations associated with it, while moment can be expressed by 3 equations as well.