ME 221 Statics

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ME 221 StaticsLecture 37Sections 8.1 8.3
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Homework 12

• Chapter 8 problems
• 1, 2, 4, 8 15
• Due Today

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No ClassFriday, December 5

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Quiz 8

• Today
• Friction problem

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Final Exam

• Section 1 (300pm)
• Monday, 12/8, 300 500pm
• Section 2 (1240pm)
• Wednesday, 12/10, 1245 245pm
• See University policy for multiple exams

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Chapter 8 - Friction

• Last Lecture

• Coulomb Friction

• Coefficients static kinematic

• Friction angle

• Today

• Wedges

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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

msN

• Kinematic coefficient, mk

mkN
W
fP
P
f
P
N
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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 ? 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.

W

• In equilibrium (P 0)
• ƒ cos ? N sin ? 0
• µs tan ?

P
f
N
?
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Example Problem