Need Help w/ The Physics of A Wheelie

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In summary, the conversation discusses the mechanics of a bike performing a wheelie while accelerating in the x-direction. The individual is seeking to understand this phenomenon through equations involving torque/moment. They mention considering the sum of moments at the axle and how the principles of "kinetic moment" provide a negative moment about that point, leading to uncertainty about how the bike would rotate. The conversation ends with a request for further explanation and consideration of other factors.
  • #1
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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  • #2
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?
 

1. What is the physics behind a wheelie?

The physics behind a wheelie involves balancing the center of mass of the bike and rider over the rear wheel while accelerating. This requires controlling the torque and angular momentum of the bike.

2. How do you maintain balance during a wheelie?

To maintain balance during a wheelie, you need to apply precise control of the throttle, clutch, and rear brakes. This allows you to adjust the torque and angular momentum of the bike to keep the center of mass in the correct position.

3. What is the role of the rear wheel in a wheelie?

The rear wheel is responsible for providing the necessary torque and angular momentum to lift the front wheel off the ground. It also acts as a pivot point for balancing the center of mass.

4. Are there any risks involved in performing a wheelie?

Yes, there are risks involved in performing a wheelie, especially if it is not done correctly. You can lose control of the bike and crash, or the bike can flip over backwards. It is important to practice in a safe environment and wear proper protective gear.

5. How can I improve my wheelie technique?

Improving your wheelie technique requires practice and understanding the physics involved. It is important to start with small wheelies and gradually increase the duration and height. You can also seek guidance from experienced riders or watch tutorials to learn proper technique.

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