-more on center of gravity -more on static equilibrium ap physics c mrs. coyle rio-antirio bridge,...
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![Page 1: -More on Center of Gravity -More on Static Equilibrium AP Physics C Mrs. Coyle Rio-Antirio Bridge, Coyle Summer 2009](https://reader036.vdocuments.pub/reader036/viewer/2022070413/5697bfe91a28abf838cb7024/html5/thumbnails/1.jpg)
-More on Center of Gravity -More on Center of Gravity -More on Static Equilibrium -More on Static Equilibrium
AP Physics CMrs. CoyleRio-Antirio Bridge, Coyle Summer
2009
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Rio-Antirio Bridge, GreeceCoyle, Summer 2009
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Ex: Minnesota Metrodome Roof Collapse
• http://www.youtube.com/watch?v=ip8sM_1tXho
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Mechanical EquilibriumMechanical Equilibrium
Translational• F=0
–Static (v=0)
–Dynamic(v=Constant)
Rotational• =0
–Static(ω=0)
–Dynamic(ω=constant)
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Necessary Condition for Necessary Condition for EquilibriumEquilibrium
1. The net (resultant) external force must be zero.
2. The net (resultant) extrenal torque must be zero about any axis.
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Static EquilibriumStatic Equilibrium
No translation• F=0
–Static (v=0)
No rotation• =0
–Static(ω=0)
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Examples: What type of Examples: What type of equilibrium exists?equilibrium exists?
1. A physics book sitting on a table.2. A skater at constant velocity.3. A spinning CD.4. The wheel of a car traveling at constant
velocity.
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When objects are in equilibrium:When objects are in equilibrium:
• Σp=0 of its center of mass.
• ΣL=0 about any axis.
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Ex: Stable Equilibrium compared Ex: Stable Equilibrium compared to Static Equilibriumto 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.
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Remember: Center of GravityRemember: 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.
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Problem Solving Strategy for Problem Solving Strategy for Static EquilibriumStatic Equilibrium
1. Draw the free body diagram of the object.
2. Set up the equations for: F=0
3. Set up the equation for: =0 (pick the axis with the simplest math).
4. Solve the equations for the unknowns.
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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
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Free Body Diagram
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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
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• Use the pivot at the wall as the axis.
• The beam’s weight acts at its CG.
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Analyze forces into x and y components
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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