Rotational stability and Fosbury Flop questions

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Discussion Overview

The discussion revolves around the concepts of rotational stability in the context of the Fosbury Flop technique in high jumping and the stability of bicycles at varying speeds. Participants explore the implications of center of gravity in high jumps and seek to identify equations related to stability in rotational motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the consequences of the center of gravity passing below the rod during the Fosbury Flop.
  • Another participant emphasizes that stability in bicycles involves multiple inter-related equations rather than a single equation, suggesting complexity in the topic.
  • Gyroscopic precession is mentioned as a simpler aspect of rotational stability, particularly in relation to torque-induced precession.
  • There is a distinction made between different types of stability in bicycles, such as stability during slow changes versus the instability experienced during high-speed maneuvers, referred to as a "tank slapper."

Areas of Agreement / Disagreement

Participants express differing views on the nature of stability in bicycles, indicating that multiple competing perspectives exist regarding the factors influencing stability at different speeds.

Contextual Notes

The discussion highlights the complexity of stability in bicycles, noting that various parameters and conditions affect the equations involved. There is also an acknowledgment of the potential for different types of stability, which may not be universally defined.

John3022
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TL;DR
Why are rotations more stable the faster they rotate and what is the consequence of the fosbury flop?
What is the consequence of the center of gravity passing below the rod in the high jump? Fosbury flop.
Which equation is responsible for a bike being more stable the faster it's driven? and in rotating things in general being more stable the faster they're rotating.
 
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Welcome, John!

Please, see:
https://www.pbs.org/newshour/science/the-not-so-hidden-physics-of-your-favorite-olympic-event

high-jump-physics-03-1200x675.png
 
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John3022 said:
Which equation is responsible for a bike being more stable the faster it's driven? and in rotating things in general being more stable the faster they're rotating.
Bicycles are complicated. There is more than one thing going on. You should not expect to find a single equation with a single unknown called "stability". Instead, you will find a collection of inter-related equations with a plethora of parameters.

Gyroscopic precession in particular is a bit simpler. You are probably concerned with torque-induced precession: https://en.wikipedia.org/wiki/Precession#Classical_(Newtonian)

The faster something is spinning, the less precession rate you get for a fixed input torque.
The faster a bike is moving, the more centripetal force you get for a fixed yaw rate.
 
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Welcome to PF. :smile:

John3022 said:
Which equation is responsible for a bike being more stable the faster it's driven?
Which kind of stability? Stability when everything is mellow and changing slowly, or the loss of stability called a "tank slapper" at speed? (Full disclosure -- I saved my one and only life threatening tank slapper merging onto a freeway at high speed in an early morning commute, and installed a steering damper on my CBR600F4 the next week).

 
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