Lower center of mass creates more stability so how do you explain moving the center of mass upwards increases stability?

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Discussion Overview

The discussion revolves around the concept of center of mass (COM) in relation to stability, particularly in the context of martial arts movements and balance. Participants explore how raising the COM can lead to increased stability, despite the common understanding that a lower COM typically enhances stability.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant notes that in martial arts, raising the arms during movements can stabilize the body, despite raising the COM.
  • Another participant suggests that increasing the moment of inertia is a factor in this stabilization.
  • A different perspective is introduced with the example of wire walkers, emphasizing that balance is crucial and that the ability to adjust the center of gravity (COG) is necessary for maintaining balance.
  • There is a question about the specifics of arm positioning during martial arts movements, indicating a need for clarity on how high the arms are raised.
  • One participant mentions that raising the COM in a small boat can lengthen the natural period of oscillation, which may make it more comfortable but could reduce stability, highlighting a nuanced view on the effects of COM height.
  • Another participant references the behavior of longer pendulums, which swing slower, suggesting a relationship between COM height and oscillation dynamics.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between COM height and stability, with no consensus reached on how raising the COM can lead to increased stability in all contexts.

Contextual Notes

Some assumptions about the conditions under which raising the COM affects stability remain unaddressed, and the discussion includes various contexts (martial arts, wire walking, and boats) that may influence the interpretation of stability.

John3022
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TL;DR
How is it possible that moving the center of mass upwards increases stability and not the opposite?
When you are doing certain movements in martial arts like kicking, you bring your arms up in order to balance yourself. Bringing your arms upwards also moves the center of mass (COM) upwards but if the COM is higher than the position should be less stable and not more stable. How do you explain the stabilizing effect of moving your COM upwards?
 
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You are increasing your moment of inertia.
 
John3022 said:
How do you explain the stabilizing effect of moving your COM upwards?
Have you ever seen a wire walker (e.g. the Great Wallenda) stroll across a wire with his arms down by his side? BALANCE matters more than COG.

EDIT: Hm ... that was not well put. Yes, balance is what's important, BUT ... you maintain balance by changing you COG, which you cannot do if your arms are by your sides. You have to be able to move your arms around to maintain your COG where it needs to be for you to not fall over.
 
Last edited:
John3022 said:
When you are doing certain movements in martial arts like kicking, you bring your arms up in order to balance yourself.
Could you show us a specific movement?
How high are the arms brought up (shoulder level or way above)?
 
John3022 said:
How do you explain the stabilizing effect of moving your COM upwards?
Moment of inertia.
For a small boat, raising the centre of mass, lengthens the natural period of oscillation, and so makes it more comfortable, but reduces stability.

Longer pendulums swing slower.
 

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