Forces can be added using arrows drawn to scale. Choose a scale, for example 1 cm for every 2 N, and draw each force as an arrow of the right length. Forces on the same line are simple: add them if they point the same way and subtract them if they point in opposite ways. A 6 N force to the right and a 2 N force to the left give a resultant force of 4 N to the right.
For two forces at right angles, draw the first arrow, then draw the second from the head of the first, head to tail. The resultant is the arrow from the start of the first to the end of the second. Measure its length and convert it back using the scale. A 6 N force and an 8 N force at right angles, drawn at 1 cm for every 2 N, give arrows 3 cm and 4 cm long. The resultant arrow measures 5 cm, so the resultant force is 10 N. Only parallel and perpendicular forces are needed.
The same method works in reverse. Resolving a force means splitting one force into two perpendicular components, for example a horizontal one and a vertical one, which together have the same effect. An object is in equilibrium when the forces on it add up to a resultant of zero. Drawn head to tail, the arrows then form a closed shape.
