12.2 Examples of Static Equilibrium – University Physics Volume 1.pdf

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9/17/21, 8:26 PM12.2 Examples of Static Equilibrium – University Physics Volume 11/3712 Static Equilibrium and Elasticity12.2 Examples of Static EquilibriumLearning ObjectivesBy the end of this section, you will be able to:Identify and analyze static equilibrium situationsSet up a free-body diagram for an extended object in static equilibriumSet up and solve static equilibrium conditions for objects in equilibrium in variousphysical situations
9/17/21, 8:26 PM12.2 Examples of Static Equilibrium – University Physics Volume 12/37All examples in this chapter are planar problems. Accordingly, we use equilibrium conditions in thecomponent form of(Figure)to(Figure). We introduced a problem-solving strategy in(Figure)toillustrate the physical meaning of the equilibrium conditions. Now we generalize this strategy in alist of steps to follow when solving static equilibrium problems for extended rigid bodies. We pro‐ceed in five practical steps.Problem-Solving Strategy: Static Equilibrium1. Identify the object to be analyzed. For some systems in equilibrium, it may be necessary toconsider more than one object. Identify all forces acting on the object. Identify the questionsyou need to answer. Identify the information given in the problem. In realistic problems,some key information may be implicit in the situation rather than provided explicitly.2. Set up a free-body diagram for the object. (a) Choose thexy-reference frame for the prob‐lem. Draw a free-body diagram for the object, including only the forces that act on it. Whensuitable, represent the forces in terms of their components in the chosen reference frame. Asyou do this for each force, cross out the original force so that you do not erroneously includethe same force twice in equations. Label all forces—you will need this for correct computa‐tions of net forces in thex– andy-directions. For an unknown force, the direction must beassigned arbitrarily; think of it as a ‘working direction’ or ‘suspected direction.’ The correctdirection is determined by the sign that you obtain in the final solution. A plus signmeans that the working direction is the actual direction. A minus signmeans that the actual direction is opposite to the assumed working direction. (b) Choose thelocation of the rotation axis; in other words, choose the pivot point with respect to which youwill compute torques of acting forces. On the free-body diagram, indicate the location of thepivot and the lever arms of acting forces—you will need this for correct computations oftorques. In the selection of the pivot, keep in mind that the pivot can be placed anywhereyou wish, but the guiding principle is that the best choice will simplify as much as possiblethe calculation of the net torque along the rotation axis.

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