When an object is in equilibrium, the resultant force acting on it is zero, and the object will either be at rest or moving with constant velocity. A resultant force represents the combined effect of two or more forces in magnitude and direction. Forces can be added by completing a parallelogram with the forces as the sides, and the diagonal of the parallelogram represents the resultant force. A single force can also be resolved into perpendicular horizontal and vertical components.

1. 2.9: FORCES IN EQUILIBRIUM

2. Forces in Equilibrium When an object is in equilibrium, the resultant force acting on it is zero. The object will either be 1. at rest 2. move with constant velocity.

3. RESULTANT FORCE A single force that represents the combined effect of two of more forces in magnitude and direction.

4. Examples( Label the forces acted on the objects)

5. Addition of Forces Resultant force, F = ____ + ____ Resultant force, F = ____ + ____

7. STEP 1 Using ruler and protractor, draw the two forces F1 and F2 from a point.

8. STEP 2 Complete the parallelogram

9. STEP 3 Draw the diagonal of the parallelogram. The diagonal represent the resultant force, F in magnitude and direction.

10. Resolution of Forces A force F can be resolved into components which are perpendicular to each other: (a) horizontal component , FX (b) vertical component, FY

11. Resolution of Forces Component of weight parallel to the plane = mg sin θ Component of weight normal to the plane = mg cosθ Fx= F cosθ Fy= F sin θ