Determining Force for Stopping Angular Motion in Rotating Body

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Discussion Overview

The discussion centers on determining the force required to stop the angular motion of a motorcycle performing a wheelie, specifically focusing on the relationship between angular momentum, torque, and force at the center of gravity. Participants explore various approaches and calculations related to this problem.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks to calculate the force exerted by a rotating body at its center of gravity during a wheelie, given known mass and angular acceleration.
  • Another participant suggests using torque equations and a practical method involving a bathroom scale to measure force, but this is challenged as not applicable to the scenario.
  • A participant highlights the need for additional information, such as lever arm length and stopping time, to convert angular momentum into force.
  • One participant proposes specific values for the wheelbase and lever arm length, suggesting a stopping time of approximately 0.3 seconds, and questions whether this leads to a simple impulse equation.
  • Another participant expresses confusion about the term "impulse equation" and seeks clarification on how to calculate angular momentum.
  • A later reply requests a clearer description of the information available and the specific information needed to resolve the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the method to calculate the required force, with multiple competing views and approaches presented. The discussion remains unresolved regarding the specific calculations and definitions needed.

Contextual Notes

Participants note limitations in the information provided, such as the need for clear definitions of angular momentum and the specific parameters required for calculations. There is also uncertainty regarding the application of impulse in this context.

Who May Find This Useful

Individuals interested in mechanics, particularly those studying angular motion, torque, and force calculations in engineering or physics contexts may find this discussion relevant.

swerider
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Hello
I am busy with a design project and need some help determining the force that can be exerted by a rotating body at its center of gravity.
Picture a motorcycle performing a wheelie, the center of gravity rotates about the rear axle. Given that the mass and angular acceleration are known, how would I find the force necessary to stop the angular motion about the rear axle at the center of gravity?
 
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Torque=(force)(distance) or T=Ia
I= moment of inertia and a is angular acceleration .
How about take a bathroom scale and lift the bike up at the angle the front tire is when doing the wheelie and set it on there . And the will give you the force and then multiply it by the distance from the center of the back wheel and this will give you the torque about that point. These are just some ideas .
 
Thanks cragar but that doesn't actually help me. I need the force resulting from the angular momentum. During a wheelie all the weight is on the back wheel anyway so putting it on a scale wouldn't tell me anything.
 
The dimensions of angular momentum are force * length * time. So there is no possible way to convert to a force without some additional information. You will need to specify the lever arm length and the stopping time. Once you have specified that then it is a simple conversion.
 
Well if the wheelbase is 1.4m, take the CG to be in the middle so lever arm will be 0.7m. Stopping time is difficult to estimate but I would say about 0.3s. Is it a simple impulse equation?
 
I don't know what you mean by impulse equation. Just take your angular momentum, divide by the lever arm length and the stopping time, and that will give you the required force.
 
Impulse is the force over time. How would I get the angular momentum? not sure of the formula
thanks
 
I'm sorry, this is confusing. I thought you already had the angular momentum.

Why don't you describe, as completely and clearly as possible, what information you have and what information you want.
 

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