Today’s Topic: Friction
 ____________
Test Your Knowledge
Friction force is determined from _____.
F=
P
P
μs = 0.5, μk = 0.4
µs – coefficient of _________________
F
Q
T (sec)
12 lb
Maximum friction force
0
Fmax =
 _____________
+x
W=12 lb
Force (N)
 _____________
Q
Friction: Pushing on a block
W
Friction force is constant; normal force
times coefficient of __________.
P
µk – coefficient of _________________
Fk =
F
N
EF 151 Spring, 2017 Lecture 2-5
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Direction of Friction Force
P
Q
5 lb
0
-5 lb
0
7 lb
0
5 lb
12 lb
7 lb
12 lb
Friction force
EF 151 Spring, 2017 Lecture 2-5
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Finding μs: Block on an Inclined Plane
Sprinter

_____________ is a type of friction force
Sliding/Slipping: ________________
Not Sliding/Slipping: _______________________
EF 151 Spring, 2017 Lecture 2-5
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EF 151 Spring, 2017 Lecture 2-5
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Pushing box across a floor
Pushing box across a floor
Find the minimum force required to start
the 50 lb box moving if the angle of the
push is 20° above horizontal.
If we push with a force of 65 lb, what is
the acceleration of the box?
μs=0.8 μk=0.6
μs=0.8 μk=0.6
What can we say about the normal force vs. the weight
EF 151 Spring, 2017 Lecture 2-5
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Homework Help:
Pushing a book up a wall
A 5 kg book is held against a wall a shown.
The angle of the push is 50° above
horizontal. The coefficient of static friction
between the book and the wall is 0.70.
a. What is the minimum force required to
start the book moving up the wall.
b. What is the minimum force required to
keep the book from sliding down the
wall?
EF 151 Spring, 2017 Lecture 2-5
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Review
Friction calculation depends on the situation
1. ________________
P
a. __________________
b. __________________
2. _________________
Direction of friction depends on: _____________________
EF 151 Spring, 2017 Lecture 2-5
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EF 151 Spring, 2017 Lecture 2-5
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