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Summary for Lecture 12 on October 15, 2007
Calculating with frictional forces:
)
static
(
N
F
)
moving
(
N
F
S
f
K
f
μ
=
μ
=
μ
varies between 0 and 1 for a large class of problems.
Moving friction has the value given, but the static friction
formula gives only the maximum possible value. The actual
value can be anywhere from zero to the maximum, and its
direction can vary according to circumstances.
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View Full Document A block sliding at 15 m/s starts up a ramp inclined at 30
0
with
respect to horizontal.
The sliding coeficient of friction between
the ramp and block is 0.4.
How far up the ramp will the block go
before it stops? Approximate the block as a point.
Construct a freebody diagram & turn it into x and Y force
equations.
(It’s convenient to use a “tilted coordinate system)
The equations can be solved to obtain the net deceleration.
1D kinematics then gives the stopping distance
v = 15 m/s
0
30
=
θ
+y
+x
Solution for block sliding up plane
( 29
( 29
( 29
( 29 ( 29
[ ]
( 29
( 29
( 29
m
6
.
13
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This note was uploaded on 04/09/2008 for the course PHYS 131 taught by Professor Reay during the Fall '08 term at Ohio State.
 Fall '08
 Reay
 Force, Friction

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