Co-planar concurrent forces are those forces which meet at one point and their lines of action also lie on the same plane
Non-coplanar concurrent forces are those forces which meet at one point, but their lines of action do not lie on the same plane.
Non-coplanar non-concurrent forces are those forces which do not meet at one point and their lines of action do not lie on the same plane.
According to Lami's theorem, if the three forces acting at a point are in equilibrium, then each force is proportional to the sine of the angle between the other two
The moment of a force
is the turning effect produced by a force, on the body, on which it acts
is equal to the product of force acting on the body and the perpendicular distance of a point and the line of action of the force
is equal to twice the area of the triangle, whose base is the line representing the force and whose vertex is the point, about which the moment is taken