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The condition of equilibrium of internal and external forces
according to (fig.7.1, b) takes the form
a
 F Q  F g x    FQ  g  x  0. (7.2)
g
Normal tension that arises in cross section rope is equal to:
Q  F  g x  a 
   1  . (7.3)


F  g 
The first factor of the resulting expression is the normal
stress under the action of an applied static load, which we denote
by  . The second factor that takes into account the effect of
c
inertia forces, called the dynamic factor and is denoted by k . It
д
is in this case:
a
k 1  . (7.4)
д
g
Then the normal stress in the rope:

  k  (7.5)
д c д
Note that in many cases the dynamic load voltage can be
determined by formula (7.5), i.e. the product of static stress on
the dynamic coefficient. Therefore, we must be able to calculate
the dynamic factor for each specific task.
Stresses in the rod that rotates with a constant angular
velocity about an axis are perpendicular to the axis of the rod (fig.
7.2 a).
Intensity distributed along the length of the rod l inertia
forces  xq is given by   x  F a , where the centripetal
q
n
acceleration section at a distance x from the axis of rotation
a   2 x . Finally,   Fxq   2 x .
n
Longitudinal strength  xN of the forces of inertia is found
from the condition of equilibrium of forces (fig.7.2, b)

l l F 2
2
  x   q ( )x dx  F 2  xdx  l  x 2  .
N
x x 2
(7.6)

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