Statics 82-1 The graphical method of composition and the equilibrium of a coplanar system of concurrent forces I The graphical method of the composition of forces 1. The composition of two concurrent forces 2. The composition of any coplanar concurrent forces 180- Fi F R R Fi F2 A A∠ A A F2 cos(1809-a)=-cosa F3 F By the parallelogram rule or constructing a force triangle According to the law of cosines The fo F orce R VF+F+2F F coSa polygon Fi According to the law of cosines F R R the direction of the resultant force is sin sin( 180=07 §2–1 The graphical method of composition and the equilibrium of a coplanar system of concurrent forces Ⅰ The graphical method of the composition of forces 2 1 2 cos 2 2 2 R = F1 + F + F F 2. The composition of any coplanar concurrent forces The force polygon: 1.The composition of two concurrent forces According to the law of cosines, the direction of the resultant force is: According to the law of cosines: cos(180−)=−cos By the parallelogram rule or constructing a force triangle. sin sin(180 ) 1  − = F R