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line of . The public was dazzled. But from the point of view of physics
it is very simple. Really, plane of oscillation of Foucault's pendulum
is nothing more than plane of rotation motion of brass sphere.
According to the law of conservation of angular momentum this plane

conserves one's own orientation in space. So when the Earth turns, the
platform of the Pantheon in Paris turns as well, and it seems that
oscillation of Foucault's pendulum changes direction.

In essence, a mechanical gyroscope is a symmetric rigid body
spinning rapidly around principal axes of inertia, that enables to
observe the special effects based on the laws of rotational motion.
. Consider a bicycle wheel that rotates around the axis OO and this

axis is located in plane YOZ as shown in fig. 6.17.

Figure 6.17

And now we make an effort to turn this axis in plane YOZ. So
that, to the axis we applied two forces , according to the right screw

rule the moment M of these forces is directed to perpendicular plane .
Аs follows from the fundamental dynamical principle for rotation of a
 
rigid body M  d L the change of direction Ld of angular momentum
dt 
of rotating body takes place in the direction of moment M .

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