Why a Ring self align when rolling forward?

Question

Explain in details why a ring (wheel, coin, etc) can self-align and keep running down the road, ramp, etc, without falling to the side. Why the rotation defies gravity? The same happens when riding a bike, you can jump out of it, the bike will continue alone, no easy falling to the side.

It seems it is associated with the forward movement and not exactly the rotation. A horizontal spinner without moving forward will fall to the side immediately.

Answer 1

It has to do with the fact that when the wheel starts to fall to one side, its path will change from straight to curved.  The relatively minor changing of direction is enough to give you a gyroscopic effect and to keep the wheel up and essentially going forward.  It is self correcting.

But, bikes are different.  They actually fall quite easily sideways if you don't make the minor adjustment in the steering, i.e., turning the front wheel in the direction of the lean.  Just weld the headset and roll the bike, it will fall to the side at the normal 9.8 m/s^2.  You will also realize this if you have to take a bike through a vary narrow path.  Suddenly the bike feels very tippy because you can't make the minute corrections.

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I am having trouble understanding your additional details.  Are you talking about how the wheel wobbles?  It all comes from momentum, just like a gyroscope, but what happens is that the bottom of the wheel will wobble going from side to side.  If it wobbles to much to the right, it will turn back to the center and overshoot to the left.  Self-correcting.  Caused by the linear momentum of the upper part of the wheel.  (basically gyro forces).

But, like I said, a bicycle is a two wheel vehicle.  It's physics are more complex.  There is no wheel wobble in the back wheel.  And the front depends of the forks and the head set.  You design a bike to be self-correcting and forgiving.  But it has its limitations.

Answer 2

It has everything to do with the rotation.  it is the conservation of angular momentum.  Each partical on the wheel will resist being turned to a new direction (newtons first). By rotating the wheel, all of the particals have a momentum that is not changed unless a force is applied.

By tilting the wheel the sum of all the particals momentums risist the change in angular momentum

this is the reason why bikes turn when you lean, the change in momentum on the wheels on the bike causes a rotational force in the direction you are leaning in.