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ILoveParticlePhysics
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You can try this at home!
Why do things with wheels get more balanced as velocity increases?
In summary: I did have one of these as a kid, but no, I don't think I'm sufficiently cool to ride that...I'm trying to find a bicycle self-stability video on an old cruiser style bike where the handlebars were removed, and a front wheel that could be turned backwards, so the forks curved backwards.
- #2
Nugatory
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There’s a pretty good explanation at http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/bicycle.html
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I was on my bike yesterday (I was on a path shared with pedestrians, so I was often going at walking speed) and I noticed that it was quite easy to balance as long as I kept moving, no matter how slowly; but not if I stopped altogether. The slower I went, the more the bike zig-zagged, which I guess is the idea of using a series of circular paths to maintain balance.
- #4
rcgldr
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The article itself stated that gyroscopic reactions play very little role in the self stability of a bike (bicycle or motorcycle). The key factor for a typical bike is a steering geometry that tends to steer the front wheel inwards if the bike is leaned. The most common method for this is called trail, if you extend an imaginary axis from the steering axis of the front wheel, it intercepts the ground ahead of the contact patch of the tire. When a bike is leaned, there is Newton third law pair of forces, the tire exerts a downwards force onto the pavement, the pavement exerts an upwards force on the leaned tire, behind the pivot axis, which causes the front tire to steer inwards. Depending on the amount of trail, there is some minimum speed for self-stability.Nugatory said:
In order to do a normal turn, the bike needs to be first leaned inwards, and this is done by steering slightly outwards so that the bike leans inwards. Counter-steering is also used to adjust lean angle.
Gyroscopic precession is a reaction to the torque related to changes in lean angle. If the lean angle is constant, gyroscopic precession is zero. Angular momentum of the front tire resists changes in the steering angle, and acts as a dampening (opposing) torque to the trail related self-stability of a bike. At moderate speeds, this prevents constant over correction. At high speeds (100+ mph), the angular momentum is so great that the bike ceases to self-correct. Mathematical formulas for infinitely thin tires predict an extremely slow inwards fall, called capsize mode, but for real tires under real circumstances, the perceived reaction is that a bike simply holds the current lean angle rather than self-correct to vertical, and requires conscious counter-steer with a lot of effort in order to change lean angle.
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- #5
Ibix
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Behind the contact patch, surely? The front forks curve forwards. Or am I misunderstanding something?rcgldr said:
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A.T.
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- #7
A.T.
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ILoveParticlePhysics said:
- #8
Ibix
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Right - forgot about the slope of the steering column. Thanks.A.T. said:
- #9
A.T.
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Are you not born to wild?Ibix said:
- #10
Ibix
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I did have one of these as a kid, but no, I don't think I'm sufficiently cool to ride that...A.T. said:
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- #11
rcgldr
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I'm trying to find a bicycle self-stability video on an old cruiser style bike where the handlebars were removed, and a front wheel that could be turned backwards, so the forks curved backwards. Unlike most road bikes, old cruiser type bikes have enough clearance for the front wheel to be turned backwards. The result is a large amount of trail, the contact patch is way behind where an imaginary extended steering axis intercepts the ground. In this configuration, the bike was stable at very slow speed, about 1.5 to 2 mph, before it fell. With the front wheel turned forwards, forks curved forwards, the trail was reduced and the bike needed to be going between 5 to 7 mph to be self stable.
1. Why do things with wheels get more balanced as velocity increases?
As velocity increases, the rotational inertia of the wheels also increases. This means that the wheels are less likely to tip over or lose balance due to external forces. Additionally, the faster the wheels are spinning, the more angular momentum they have, providing a stabilizing force.
2. How does the shape of the wheel affect its balance at high velocities?
The shape of the wheel plays a crucial role in its balance at high velocities. A wheel with a larger radius has a higher rotational inertia, making it more stable at high speeds. Additionally, a wheel with a wider base or larger contact patch with the ground will have more stability compared to a narrow wheel.
3. Does the weight of the wheel affect its balance at high velocities?
Yes, the weight of the wheel can impact its balance at high velocities. A heavier wheel will have a higher rotational inertia, making it more stable. However, if the wheel is too heavy, it may also be more difficult to accelerate, resulting in slower speeds.
4. How does the surface on which the wheel is rolling affect its balance at high velocities?
The surface on which the wheel is rolling can have a significant impact on its balance at high velocities. A smooth and flat surface will provide less resistance and allow the wheel to maintain its balance more easily. On the other hand, a rough or uneven surface can cause the wheel to lose balance and potentially tip over.
5. Are there any other factors that contribute to the balance of wheels at high velocities?
Yes, there are other factors that can affect the balance of wheels at high velocities. These include the air resistance or drag on the wheel, the distribution of weight on the wheel, and the type of material the wheel is made of. All of these factors can impact the rotational inertia and stability of the wheel at high speeds.
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