Need Help w/ The Physics of A Wheelie

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SUMMARY

The discussion focuses on the physics of performing a wheelie on a bike while accelerating, specifically analyzing the torque and moments involved. The user seeks clarification on how the torque from static friction can overcome the torque from weight to allow the bike to rotate counter-clockwise about the rear axle. Key concepts include the balance of moments at the axle, where the static friction must exceed the clockwise moment caused by weight for the front wheel to lift. The conversation emphasizes the importance of understanding kinetic moments and their impact on bike dynamics.

PREREQUISITES
  • Understanding of torque and moment calculations
  • Familiarity with free body diagrams (FBD)
  • Knowledge of static and kinetic friction principles
  • Basic physics concepts related to rotational motion
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  • Study the principles of torque in rotational dynamics
  • Learn about the role of static friction in motion and stability
  • Explore the concept of free body diagrams in physics
  • Investigate the effects of acceleration on rotational motion
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This discussion is beneficial for physics students, mechanical engineers, and cycling enthusiasts interested in understanding the mechanics of bike dynamics during stunts like wheelies.

NJD21
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So the attachment has my FBD of a bike.

What I'm trying to understand is how exactly a bike does a wheelie while accelerating (in the x-direction) by applying equations involving torque/moment.

For equations involving torque/moment:

So if I take the sum of the moments at the axle, I assumed the torque from the static friction should overcome the torque from the weight so that the bike rotates about that point in the counter-clockwise direction; however when applying principles involving "kinetic moment", (mass x acceleration) provides a negative moment about that point (clockwise rotation). And because of this negative moment, I'm not sure how the bike would be rotating about the rear axle.

Any help is appreciated. Thanks.
 

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NJD21 said:
when applying principles involving "kinetic moment", (mass x acceleration) provides a negative moment about that point (clockwise rotation).
Can you explain that part more?
In your diagram, you correctly have the friction forwards on the back wheel at contact with the road, so this provides an anticlockwise moment. If that exceeds the clockwise moment from the weight, the front wheel will lift. What else is there to consider?
 

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