Engineering Mechanics Lecture 3

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Engineering MechanicsLecture 3

• 5/10, Friday
• 4-5am

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Tendency of Force to Rotate a Body

• Two effects of force
• Move a body in the direction of its application
• Rotate a body around an axis.

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Moment Arm
Tendency of the force to rotate a body Is
proportional to F and d
d perpendicular distance from the axis to the
line of force action
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Right-Hand Rule
Moment in the direction of thumb
Fingers curl in the direction of the tendency to
rotate
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Sign of Moment (2D Convention)
Plus sign () counter clockwise Minus sign (-)
clockwise
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Many-Particle Interactions
For an N particles system, in equilibrium
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F3
f32
f23
f31
2
f13
f21
f12
F1
1
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Many-Particle Interactions
Newtons 1st law
For an N particles system, in equilibrium
Can you prove
?
Need Newtons 3rd law
Therefore
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Many-Particle System
For a N-particle system, in equilibrium