![]() Thrust Bearings Bearings designed to prevent axial motion of the object they support Are there true rigid bodies in Nature? No. Explain Self Aligning bearings Conventional bearings that are required to be perfectly aligned so that it is justified to assume the moment reactions are zero. What are ways to eliminate moments reactions in bearings? Use a special type of bearing called a self-aligning bearing or by the use of two or more perfectly aligned bearings that are on the same axis. Describe the moment of a bearing? Has two moment reactions. ![]() What is a way to determine the forces and moments for a particular support? Consider the motion the support prevents. What is another way to describe an objects fixity? An object's ability to undergo rigid body motion What is the difference between analysis of 3D and 2D rigid body equilibrium? 3D has more intricate FBDs, reactions are more complex, and # of unknowns and # of equations are greater. Or all lines of action are parallel > parallel force system) Zero-Force member any body that is not subjected to any force General multiforce member a body is subjected to forces at more than 3 points and/or has moment loading and/or has distrusted loading. When in equilibrium, the lines of action of all three forces intersect at a common point. (No moment loading and no distributed forces such as weight) When in equilibrium, the two forces have the same line of action and opposite directionsĪ member that is subjected to no moments and has forces applied at only two points Three-Force Member A body subjected to forces at 3 points. Two-Force Member A body subjected to forces at two points (no moment loading or distributed forces like weight). HOWEVER, they if a body does have motion capability, the forces/ moments determine whether or not motion actually occurs or not. It may have full or partial fixity How do forces and moments play a role in Rigid body motion capability? They don't! They have nothing to do with it. ![]() Unknowns 3 Body is statically indeterminate more unknowns than 3 (or the number of equations we have) What is the purpose of Equation Counting? Determine if an object is statically determinate or indeterminate by comparing the number of unknowns to the number of equilibrium equations. Statically Determinate Body the equilibrium equations in statics are sufficient to determine all unknowns Statically indeterminate Body the equilibrium equations in statics are NOT sufficient to determine all unknowns. Translation in two orthogonal directions and rotation (or any combination) What is required in 2D for an a body to have complete fixity? Supports having a total of three of more reaction forces and/or moments with suitable arrangement. No Fixity Full Rigid body motion capabilityĪ body with no supports and is free to translate and rotate in space Types of "Rigid body motion" in 2D Three Types
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