ME 221 Statics
Lecture #37
Sections 8.1 – 8.3
ME221
Lecture 36
1
Homework #12
Chapter 8 problems:
– 1, 2, 4, 8 & 15
Due Today
ME221
Lecture 36
2
No Class
Friday, December 5
ME221
Lecture 36
3
Quiz #8
Today
Friction problem
ME221
Lecture 36
4
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
ME221
Lecture 36
5
Chapter 8 - Friction
• Last Lecture
– Coulomb Friction
• Coefficients – static & kinematic
– Friction angle
• Today
– Wedges
ME221
Lecture 36
6
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
ME221
N
P
Lecture 36
7
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
ME221
Lecture 36
8
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
ME221
Lecture 36
9
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
ME221

Lecture 36
10
Example Problem
ME221
Lecture 36
11