Is angular momentum perpendicular to fixed axis of rotation constant?

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SUMMARY

The discussion centers on the behavior of angular momentum in relation to a fixed axis of rotation, specifically addressing the effects of torques that are perpendicular to this axis. It is established that when sufficient restraints are present, these torques can be ignored, allowing the angular momentum perpendicular to the axis to remain constant. The inquiry also explores whether a hinged rod's angular momentum changes direction at various points during its rotation, questioning the nature of the torques involved.

PREREQUISITES
  • Understanding of angular momentum and its properties
  • Familiarity with torque and its effects on rotational motion
  • Basic knowledge of rigid body dynamics
  • Concept of fixed axes in rotational systems
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  • Study the principles of torque in rotational dynamics
  • Explore the concept of angular momentum conservation in closed systems
  • Learn about the effects of external forces on angular momentum
  • Investigate the dynamics of hinged rods and their motion
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This discussion is beneficial for physics students, educators, and anyone interested in the principles of rotational dynamics and angular momentum analysis.

TahirMaqbool
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TL;DR
Does the component of angular momentum perpendicular to the fixed axis of rotation change in direction or magnitude?
So my book states torques perpendicular to the fixed axis of rotation tend to tilt the axis , however we assume sufficient restraints exist so these torques are simply ignored.
It follows that angular momentum perpendicular to axis remians constant.
(See image )

My question is that if a rod is hinged at one of its ends and allows to rotate, wouldn't angular momentum perpendicular to axis change in direction at each point?
See image below.
 

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Are those “torques perpendicular to the fixed axis of rotation” also contained in the plane that is “perpendicular to the fixed axis of rotation”?
 

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