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ch3 online ppt - Ch 3 Equilibrium 3.0 Outline Mechanical...

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Ch. 3: Equilibrium 3.0 Outline 123 Mechanical System Isolation (FBD) 125 2-D Systems Equilibrium Conditions 144 3-D Systems Equilibrium Conditions 174 3.0 Outline 123
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Ch. 3: Equilibrium 3.0 Outline When a body is in equilibrium, the resultant on the body is zero. And if the resultant on a body is zero, the body is in equilibrium. So, is the necessary and sufficient conditions for equilibrium. 3.0 Outline ∑∑ F=0 M=0 124
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Ch. 3: Equilibrium 3.1 Mechanical System Isolation (FBD) Free-Body Diagram (FBD) is the most important first step in the mechanics problems. It defines clearly the interested system to be analyzed. It represents all forces which act on the system. The system may be rigid, nonrigid, or their combinations. The system may be in fluid, gaseous, solid, or their combinations. FBD represents the isolated / combination of bodies as a single body. Corresponding indicated forces may be 1. Contact force with other bodies that are removed virtually. 2. Body force such as gravitational or magnetic attraction forces. 3.1 FBD 125
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Ch. 3: Equilibrium 3.1 FBD 126
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Ch. 3: Equilibrium 3.1 FBD Remarks 1. Force by flexible cable is always a tension. Weight of the cable may be significant. 2. Smooth surface ideally cannot support the tangential or frictional force. Contact force of the rough surface may not necessarily be normal to the tangential surface. 3. Roller, rocker, smooth guide, or slider ideally eliminate the frictional force. That is the supports cannot provide the resistance to motion in the tangential direction. 4. Pin connection provides support force in any direction normal to the pin axis. If the joint is not free to turn, a resisting couple may also be supported. 127
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Ch. 3: Equilibrium 3.1 FBD 128
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Ch. 3: Equilibrium 3.1 FBD Remarks 5. The built-in / fixed support of the beam is capable of supporting the axial force, the shear force, and the bending moment. 6. Gravitational force is a kind of distributed non-contact force. The resultant single force is the weight acted through C.M. towards the center of the earth. 7. Remote action force has the same overall effects on a rigid body as direct contact force of equal magnitude and direction. 8. On the FBD, the force exerted on the body to be isolated by the body to be removed is indicated. 9. Sense of the force exerted on the FBD by the removed bodies opposes the movement which would occur if those bodies were removed. 129
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Ch. 3: Equilibrium 3.1 FBD Remarks 10. If the correct sense cannot be known at first place, the sense of the scalar component is arbitrarily assigned. Upon computation, a negative algebraic sign indicates that the correct sense is opposite to that assigned. 130
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Ch. 3: Equilibrium 3.1 FBD Construction of FBD 1. Make decision which body or system is to be isolated. That system will usually involve the unknown quantities.
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This note was uploaded on 10/04/2011 for the course ESM 2104 at Virginia Tech.

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ch3 online ppt - Ch 3 Equilibrium 3.0 Outline Mechanical...

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