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MILHDBK1013/14
where:
FF = road friction force
f = friction coefficient
w = vehicle weight
NOTE: The value of friction coefficient, "f," is between 0 and 1 and is highly
variable. It depends on the tire and its condition, the material and condition of the drive path,
any oil or water on the drive surface, etc. On a roadway, under normal conditions, f = 0.6 is
usually used. If unable to determine, use f = 1, which will provide a more conservative value.
a) On a Horizontal Surface. The skidding speed (the speed at which skidding occurs),
"vS," is obtained by equating the centrifugal force and the road friction force, as shown in Equations
(5) and (6).
fw = wv 2 /(gr)
EQUATION:
(5)
S
where:
f
= friction coefficient
w
= vehicle weight
vS
= skidding speed
g
= gravitational constant
r
= radius of curvature
From which,
fgr
vS =
EQUATION:
(6)
where:
vS = skidding speed
f = friction coefficient
g = gravitational constant = 32.2 feet per second squared (9.82 meters per second
squared)
r = radius of curvature
Because "v" must be made as small as possible for the most costeffective protection,
this relationship suggests that options for the physical security planner include making the drive
path slippery, with a small radius of curvature, or both. The above relationship is plotted as Figure
7, using "f " as a parameter using a conversion factor for values in ft and mph.
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