ME 221 Statics
Lecture #36
Sections 8.1 – 8.3
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Homework #12
Chapter 8 problems:
– 1, 2, 4, 8 & 15
Due Today
ME221
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Quiz #8
Today
Friction problem
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Final Exam
Section 1 (3:00pm)
Monday, 12/8, 3:00 – 5:00pm
Section 2 (12:40pm)
Wednesday, 12/10, 12:45 – 2:45pm
See University policy for multiple exams
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Chapter 8 - Friction
• Last Lecture
– Coulomb Friction
• Coefficients – static & kinematic
– Friction angle
• Today
– Wedges
– Course Evaluations
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Coulomb Friction (dry friction)
• Friction force (ƒ) is proportional to the
normal force (N) and opposes motion
• Coefficient of friction, m, is the
proportionality constant
f
– Static coefficient, ms
– Kinematic coefficient, mk
W
msN
mkN
f=P
P
f
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N
P
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Friction: Wedges
• Wedges are a simple means for lifting
• Again, friction force opposes the motion
• FBDs are essential for solving problems
– Apply equilibrium equations to FBDs
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Friction: Wedges
• Wedges may exert large normal forces
• Used to lift heavy objects
• Also used for splitting
– Friction holds wedge in place
• May be used in pairs
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Wedges
• The angle θ is called the wedge angle, and it
determines the amount of force P required to raise
the weight W, as well as the change in height of
the weight as the wedge is driven into place.
• In equilibrium (P = 0):
ƒ cos θ – N sin θ = 0
• μs = tan θ
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
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Example Problem
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