Statics Conclusion: R=F+F+F,+E In general: R-EF The resultant of a coplanar system of concurrent forces is equal to the geometrical sum of these forces and it applies to the point of intersection of these forces. II The graphical condition of equilibrium The necessary and sufficient condition is R=∑F=0 If the resultant force is zero the force F2 F polygon draw with these forces is closed So the graphical condition of equilibrium of a coplanar system of concurrent forces is F5 R The force polygon is closed or The geometrical sum of all forces is zero.9 Conclusion: In general: The resultant of a coplanar system of concurrent forces is equal to the geometrical sum of these forces and it applies to the point of intersection of these forces. Ⅱ The graphical condition of equilibrium R=F R F1 F2 F3 F4 = + + + If the resultant force is zero, the force polygon draw with these forces is closed. So the graphical condition of equilibrium of a coplanar system of concurrent forces is: The necessary and sufficient condition is: R=F =0 The force polygon is closed or The geometrical sum of all forces is zero