Rotational weight vs dead weight

  • Context: High School 
  • Thread starter Thread starter mrwabba
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    Rotational Weight
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Discussion Overview

The discussion revolves around the stability of a motorcycle at a dead stop while the engine is running at 15,000 RPM. Participants explore the concepts of angular momentum, gyroscopic effects, and the relationship between engine power and motorcycle balance.

Discussion Character

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

Main Points Raised

  • Some participants suggest that the motorcycle's stability while stationary could be influenced by the engine's rotational force, which is mounted parallel to the wheels.
  • One participant explains that stability is related to angular momentum, noting that spinning wheels contribute to this stability and that tipping would cause the angular momentum vector to tilt up.
  • Another participant argues that for the engine's spin to contribute to stability, it must generate sufficient angular momentum, which depends on the moment of inertia and speed of the engine.
  • A participant proposes a formula involving the engine's power and the motorcycle's mass and center of mass height to assess the potential for the motorcycle to stand due to gyroscopic forces.
  • There is a request for clarification on how to calculate the power of the engine in watts.

Areas of Agreement / Disagreement

Participants express differing views on the role of the engine's rotational force and the conditions under which it may contribute to the motorcycle's stability. The discussion remains unresolved regarding the effectiveness of the engine's spin in maintaining balance.

Contextual Notes

Participants reference concepts such as angular momentum and gyroscopic effects without reaching a consensus on the specific conditions necessary for stability. There are also unresolved questions about the calculations related to engine power.

Who May Find This Useful

Individuals interested in motorcycle dynamics, physics of rotation, and stability analysis may find this discussion relevant.

mrwabba
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I herd an argument about a motorcycle that said at a dead stop could a motorcycle balance while turning 15,000 RPM? I know while riding the object being in motion along with the tires rotating keep the motorcycle on 2 wheels. My question is could the engines turning force keep it balanced? The engine is mounted so it rotates parallel to the wheels so it does add some balance and it’s not trying to throw the bike to one side.
 
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mrwabba said:
I herd an argument about a motorcycle that said at a dead stop could a motorcycle balance while turning 15,000 RPM? I know while riding the object being in motion along with the tires rotating keep the motorcycle on 2 wheels. My question is could the engines turning force keep it balanced? The engine is mounted so it rotates parallel to the wheels so it does add some balance and it’s not trying to throw the bike to one side.
Stability has to do with angular momentum. Spinning wheels have angular momentum. The bike will be vertically stable because tipping causes the angular momentum vector to tilt up. In order to conserve angular momentum, the bike has to rotate in the horizontal plane (about a vertical axis). But the friction of the two wheels on the road prevents a rotation of the bike about a vertical axis.

In order for the engine spin to make the bike stable, it would have to create angular momentum to produce a gyroscope effect. Since L = Iw, you need the engine to have significant moment of inertia or high speed or a combination of both. A crankshaft doesn't have much moment of inertia.

AM
 
Take the power of the engine (wattage) and divide this by pi*15,000 rpm.

If this value is greater then half the mass (kilograms) of the bike multiplied by the height of the bike's center of mass (meters) squared, then the bike has some chance of standing up due to gyroscopic force.
 
thanks for both of the replys. how you be able to figure out the power of the engine in watts?
 

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