Chapter 3 Equilibrium

Equilibrium – Condition where the net force and net moment are both zero. Both conditions must be zero for a system to be in equilibrium! Free-Body Diagrams: A free-body diagram is a representation of an isolated system as a single object, upon which all of the external forces acting on the system are drawn. This is the most important single steps in the solution of problems in mechanics.

Drawing a free-body diagram: 1.Determine the system to be studied. 2.Isolate System. a.Choose to examine a single object or a group of objects b.Draw an outline of your system (the internal structure of the system is not important!) 3.Determine direction and point of application of all forces. a.If the direction of a force is unknown choose an arbitrary direction. It is best to make an educated guess to the appropriate direction. b.The point of application is important for determining moments! 4.Define coordinate system and reference everything to this reference frame. a.The most common choice of reference frame is a Cartesian reference frame (x, y and z), but this in not the only choice! b.Choose the most appropriate reference frame to simplify your solution. Choosing a reference frame that is aligned with multiple forces is often convenient!

The situations shown represent incomplete free-body diagrams. Complete the diagrams with the appropriate forces. The weights of the bodies are negligible unless otherwise indicated. Dimensions and numerical values are omitted for simplicity.

The situations shown represent incomplete or incorrect free- body diagrams. Complete or correct the diagrams with the appropriate forces. The weights of the bodies are negligible unless otherwise indicated. Dimensions and numerical values are omitted for simplicity.

Draw a complete and correct free- body diagram for body/bodies indicated in each of the situations shown. The weights of the bodies are negligible unless otherwise indicated. Dimensions and numerical values are omitted for simplicity. Note: The sense of some reaction components cannot always be determined without numerical calculation.