Perpendicular Triangle Law of Forces:
The perpendicular triangle law of forces is the direct outcome of the triangle law of forces. The law can be stated below.
If three forces acting at a point are such that they are proportional to the sides of a triangle and their directions are perpendicular to the corresponding sides, all inwards or all outwards, then the forces will be in equilibrium.
If the triangle is rotated in its own plane through one right angle in an anticlockwise direction, then this new triangle will have the sides, in order, parallel to the given forces, and the forces are proportional to the corresponding sides of the triangle.
Hence, by the triangle law of forces, they are in equilibrium.
The converse of the perpendicular triangle law of forces is also true. It can be stated as follows.
If three forces acting at a point are in equilibrium and their lines of action are perpendicular to the sides of a triangle, then their magnitudes will be proportional to the sides to which they are perpendicular.