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-More on Center of Gravity -More on Static Equilibrium

-More on Center of Gravity -More on Static Equilibrium. AP Physics C Mrs. Coyle. Rio-Antirio Bridge, Coyle Summer 2009. Rio-Antirio Bridge, Greece Coyle, Summer 2009. Ex: Minnesota Metrodome Roof Collapse. http://www.youtube.com/watch?v=ip8sM_1tXho. Mechanical Equilibrium. Translational.

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-More on Center of Gravity -More on Static Equilibrium

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  1. -More on Center of Gravity -More on Static Equilibrium AP Physics C Mrs. Coyle Rio-Antirio Bridge, Coyle Summer 2009

  2. Rio-Antirio Bridge, GreeceCoyle, Summer 2009

  3. Ex: Minnesota Metrodome Roof Collapse • http://www.youtube.com/watch?v=ip8sM_1tXho

  4. Mechanical Equilibrium Translational Rotational St=0 Static(ω=0) Dynamic(ω=constant) • SF=0 • Static (v=0) • Dynamic(v=Constant)

  5. Necessary Condition for Equilibrium • The net (resultant) external force must be zero. • The net (resultant) extrenal torque must be zero about any axis.

  6. Static Equilibrium Notranslation Norotation St=0 Static(ω=0) • SF=0 • Static (v=0)

  7. Examples: What type of equilibrium exists? • A physics book sitting on a table. • A skater at constant velocity. • A spinning CD. • The wheel of a car traveling at constant velocity.

  8. When objects are in equilibrium: • Σp=0 of its center of mass. • ΣL=0 about any axis.

  9. Ex: Stable Equilibrium compared to Static Equilibrium • When an object returns to static equilibrium after it undergoes a displacement it is in stable equilibrium. • Ex: A steel ball at the bottom of a bowl when moved to the side of the bowl, returns to the bottom and eventually stops.

  10. Remember: Center of Gravity • The point of the object where the force of gravity is thought to be acting. • Average location of weight. • If g is the same throughout the object then the CM coincides with the CG.

  11. Problem Solving Strategy for Static Equilibrium • Draw the free body diagram of the object. • Set up the equations for: SF=0 • Set up the equation for: St=0 (pick the axis with the simplest math). • Solve the equations for the unknowns.

  12. Ex: 12.2 • A person holds a 50N ball. • Find the upward force exerted by the bicep on the forearm and acting at the joint. Neglect the weight of the forearm. • Ans: 583N

  13. Free Body Diagram

  14. Ex: 12.3 • A uniform beam is attached to a wall by a pin connection. A 600N person stands 2m from the wall. Find the tension in the cable and the magnitude and direction of the force exerted by the wall on the beam. • Ans: 313N, 580N , 71.10

  15. Use the pivot at the wall as the axis. • The beam’s weight acts at its CG.

  16. Analyze forces into x and y components

  17. Ex: 12.4 • A uniform ladder of mass m and length l, rests against a smooth vertical wall. If the coefficient of static friction between the ground and the ladder is 0.40, find the minimum angle θat which the ladder would not slip. • Ans:510

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