Apparent Initial Acceleration due to Precession of Wheel Gyroscope?

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Discussion Overview

The discussion centers on the dynamics of a wheel gyroscope, particularly focusing on the apparent initial acceleration of its center of mass (CoM) during precession. Participants explore the forces involved, the nature of torque, and the motion of the gyroscope in relation to its support system. The scope includes theoretical explanations and conceptual clarifications regarding gyroscopic motion and forces acting on the system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant defines the center of mass and describes the precession of a gyroscope, questioning the source of acceleration when the gyroscope is released.
  • Another participant suggests that the force for the circular motion of the CoM originates from the support, noting that if the gyroscope is spun on a slippery surface, the support will move instead of the CoM.
  • A participant requests clarification on how the wheel begins to move in the horizontal plane and asks about the forces in a referenced diagram.
  • One participant critiques a diagram, stating that the chain will not hang vertically but will create a small angle with the vertical, producing a restoring force that acts as the centripetal force during precession.
  • A question is raised about the behavior of the support if it is not fixed to the ground, inquiring whether it would rotate around the CoM.
  • A participant acknowledges the presence of torque due to gravity and the reaction force from the chain, mentioning pseudoregular precession in rapidly spinning tops.
  • The same question about the support's movement is reiterated, with a participant confirming that if the support can only exert a vertical force, the CoM will not move but will precess around the center.

Areas of Agreement / Disagreement

Participants express varying views on the forces acting on the gyroscope and the behavior of the support system. There is no consensus on the initial conditions of motion or the precise nature of the forces involved, indicating that multiple competing views remain.

Contextual Notes

Some assumptions regarding the system's constraints and the definitions of forces are not fully explored, leaving certain aspects of the discussion unresolved.

HakimTem
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The center of mass of a system is defined as a point that acts as if all the mass is concentrated on that one point whereby all forces may act on it. With a wheel gyroscope as an example where the center of mass is in the middle of the wheel when the wheel is spun and let go, the wheel undergoes precession whereby it rotates around its support. This comes from the nature of torque by gravity on the wheel changing its angular momentum. However, why does the center of mass gain an acceleration when it's let go to pursue a circular orbit? And which force causes such acceleration?
 
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The force for the circular motion of the CoM comes from the support. If you spin the gyroscope on something slippery the CoM will stay in place and the support will make a circle instead.
 
So if using this as a diagram
f0409.gif

how does the wheel initially start moving in the horizontal plane and where are the forces labeled on the diagram?
 
That diagram is not accurate. The chain will not hang vertically, but will make a small angle with the vertical. This small angle with the vertical will produce a restoring force like any pendulum. The restoring force will serve as the centripetal force for the circular motion of the CoM as it precesses.
 
So if the support is not supported by the ground and is allowed to move with the wheel then it would rotate around the center of mass?
 
HakimTem said:
So if the support is not supported by the ground and is allowed to move with the wheel then it would rotate around the center of mass?
Yes. If the support cannot provide any horizontal force, but only a vertical force, then the center of mass will not move. It will just precess around the center.
 

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