While you are beginning to learn about [[183_notes:torque|how objects rotate]], it's worth taking an aside to discuss how objects remain still. You have already begun this work, when you read about [[183_notes:freebodydiagrams|Free Body Diagrams]] and worked with [[183_notes:youngs_modulus|Young's Modulus]]. In both those cases, you read that an object at rest will remain at rest ([[183_notes:momentum_principle|it won't change its momentum]]) as long as the net force acting on the object is zero. It turns out that isn't the complete story. **In these notes, you will read about static equilibrium, how the concept of torque plays a key role in defining static equilibrium, and how we analyze static equilibrium situations.**
While you are beginning to learn about [[183_notes:torque|how objects rotate]], it's worth taking an aside to discuss how objects remain still. You have already begun this work, when you read about [[183_notes:freebodydiagrams|Free Body Diagrams]] and worked with [[183_notes:youngs_modulus|Young's Modulus]]. In both those cases, you read that an object at rest will remain at rest ([[183_notes:momentum_principle|it won't change its momentum]]) as long as the net force acting on the object is zero. It turns out that isn't the complete story. **In these notes, you will read about static equilibrium, how the concept of torque plays a key role in defining static equilibrium, and how we analyze static equilibrium situations.**
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==== Lecture Video =====
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{{youtube>RzA8uywxjzc?large}}
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===== Defining Static Equilibrium =====
===== Defining Static Equilibrium =====
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Line 24:
∑Fx=0∑Fy=0
∑Fx=0∑Fy=0
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If the sum of all the forces is zero then static equilibrium is possible but **not** guaranteed.
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//If the sum of all the forces is zero then static equilibrium is possible but **not** guaranteed.//
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[{{ 183_notes:statics_bar.png?250|A bar with two identically sized forces acting on it.}}]
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[{{ 183_notes:week12_staticpivotforces.png?350|A bar with two identically sized forces acting on it.}}]