Engineer Physisist question
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Engineer Physisist question
I ride a bicycle. I know it is easier to keep from falling over the faster I am going.
Why?
Why?
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Law of conservation of angular momentum.
You have several gyroscopic stabilization devices on your bicycle.
You have several gyroscopic stabilization devices on your bicycle.
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I think not. It isn't gyroscopic effects that keep you upright- if so, they'd keep you from steering, too, would they not? But, the way you balance on a bike is basically by steering the front wheel so the bike stays underneath you. The speed at which the front of the bike moves sideways when you steer is proportional to your speed. So when you go faster, a slight movement will promptly put the bike back under you. At very slow speeds, exaggerated movements are required to accomplish the same thing.
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It is a much more complicated question than usually assumed; however, one component that is important is the rider's sense of balance. No matter what speed your riding you CAN fall. There are a number of forces involved, all of which can be overcome and face plant you if you move the wrong way on the bike.
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[url="https://www.youtube.com/watch?v=2Y4mbT3ozcA"]Why bicycles do not fall: Arend Schwab at TEDxDelft - YouTube
But I don't really think it answer the question.
But I don't really think it answer the question.
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Here is another angle. Suppose you are tipping over a bit. Then to avoid falling over you will want to steer in a circle so that the forcing pulling you over is the same as the centripetal force keeping you in a circle. Centripetal force is v^2/r - so the radius of the turn required will be proportional to the square of your velocity. Go twice as fast and the radius becomes four times as much. At high speed you can stay up with wide shallow arcs while at low speed you'll need sharper zig-zags.
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If you want to try to figure out something really weird. I pushed someone's seat (saddle) once while biking myself and I fell. Can you believe that? I fell.
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It is the bike and not the rider. Push a bike without a rider, and it will stay upright by itself until it almost stops.
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And rider balance is why a bike with a rider is not the same machine as the bike without the rider you described. A bike with a rider is able to stay upright and balanced with no movement what so ever (track stand). It is the riders ability to balance that allows the machine (the combination of rider and bicycle) to compensate for changing forces such a tires slipping on mud or speeding up in a sharp turn to counter tires slipping out etc...
To emphasize the role that the riders sense of balance plays, consider that folks with balance disorders find riding a bike nearly impossible.
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i thought this is common knowledge.
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Is there really an answer to the OP question?
Just thinking it through i can think of the deformation of the frame with the added weight of the rider and everytime the rider pushes on the pedal, bump on the road which pushes the wheel in all directions, wind, inclination of the road, the rider balance or even the longer or shorter leg or arm of the rider, even temperature which can mess things up even more. I don't know.
Just thinking it through i can think of the deformation of the frame with the added weight of the rider and everytime the rider pushes on the pedal, bump on the road which pushes the wheel in all directions, wind, inclination of the road, the rider balance or even the longer or shorter leg or arm of the rider, even temperature which can mess things up even more. I don't know.
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This topic is actually endless fun to explore!
A bike on its own tends to spiral down to a crash. it doesn't just tip over the way it would if it were stationary. Actually with a stationary bike the front wheel all too often turns sharply and the bike goes down. When I park my bike I have a strap to hold the front wheel to the down tube to prevent that from happening.
With many bikes it is easy to ride no-hands for long distances, following curves in the road etc. But bikes do vary a lot in how easy that is.
Another fascinating related topic is shimmy. I live in bear country. I want to do some bike camping, so I got myself a bear canister for storing food. I just took it out on a test ride, strapping it on the back of my rear rack. Lo and behold, that got my bike to shimmy, which it normally doesn't do! A shimmy is an oscillation. That happens when there is a restoring force with some inertia to carry it past the center and when there is not enough damping. Easy to see that the bear canister increased the inertia so that's why the shimmy started. But the phenomenon of shimmy also shows that a bike has a kind of restoring force that doesn't involve a person steering.
A bike on its own tends to spiral down to a crash. it doesn't just tip over the way it would if it were stationary. Actually with a stationary bike the front wheel all too often turns sharply and the bike goes down. When I park my bike I have a strap to hold the front wheel to the down tube to prevent that from happening.
With many bikes it is easy to ride no-hands for long distances, following curves in the road etc. But bikes do vary a lot in how easy that is.
Another fascinating related topic is shimmy. I live in bear country. I want to do some bike camping, so I got myself a bear canister for storing food. I just took it out on a test ride, strapping it on the back of my rear rack. Lo and behold, that got my bike to shimmy, which it normally doesn't do! A shimmy is an oscillation. That happens when there is a restoring force with some inertia to carry it past the center and when there is not enough damping. Easy to see that the bear canister increased the inertia so that's why the shimmy started. But the phenomenon of shimmy also shows that a bike has a kind of restoring force that doesn't involve a person steering.
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I think not. It isn't gyroscopic effects that keep you upright- if so, they'd keep you from steering, too, would they not? But, the way you balance on a bike is basically by steering the front wheel so the bike stays underneath you. The speed at which the front of the bike moves sideways when you steer is proportional to your speed. So when you go faster, a slight movement will promptly put the bike back under you. At very slow speeds, exaggerated movements are required to accomplish the same thing.
Steering at any reasonable speed is accomplished mostly through LEANING, rather than turning the bar; the high center of gravity of the rider, plus the rider's weight, is enough to overcome the gyro effect. This is evident by no-hands steering, which is done by minute weight shifts. The higher the speed, also, the easier steering is, due to CENTRIPETAL force, which eases the effort of leaning into the turn.
Funny -- your reasons/arguments AGAINST gyro effect substantiate it...!
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Gyroscopic, trail, center of mass of the steering part. The bike is self-stable if it naturally turns into the lean.
The gyro isn't really a big part of it, mainly precession serving to turn the wheel into the lean.
The gyro isn't really a big part of it, mainly precession serving to turn the wheel into the lean.
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I think trail is the main thing. The wheel contacts the ground behind the steering axis - how far behind, that's the trail. When the bike is leaning a bit to one side, the ground pushing on the wheel will push the back part of the wheel up, which makes the front part of the wheel turn down toward the ground, i.e. into the turn.
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Have you ever seen that carnival booth with the bicycle that has reverse handlebars? You turn left, the wheel goes right. If you can ride it a certain distance, you win a prize.
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Definitely a good way to explore what makes a bike easy to ride is to make a bike that is difficult or impossible to ride. For the carnival bike, I would try just riding it no-handed!
Here is a nice article that opens up some of the complexity of the problem:
https://janheine.wordpress.com/2011/0...orks-together/
Here is a nice article that opens up some of the complexity of the problem:
https://janheine.wordpress.com/2011/0...orks-together/
#23
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Here is another angle. Suppose you are tipping over a bit. Then to avoid falling over you will want to steer in a circle so that the forcing pulling you over is the same as the centripetal force keeping you in a circle. Centripetal force is v^2/r - so the radius of the turn required will be proportional to the square of your velocity. Go twice as fast and the radius becomes four times as much. At high speed you can stay up with wide shallow arcs while at low speed you'll need sharper zig-zags.
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Pedaled too far.
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Sir Isaac Newton explained it. A body in motion tends to stay in motion. Inertia. Once you get going in a direction, you tend to stay going in that direction.
Gyroscopic stabilization has been disproved
Here are a couple of articles
https://arstechnica.com/science/2011/...ns-we-thought/
https://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf
Gyroscopic stabilization has been disproved
Here are a couple of articles
https://arstechnica.com/science/2011/...ns-we-thought/
https://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf
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Last edited by Artkansas; 08-10-13 at 10:36 PM.
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Sir Isaac Newton explained it. A body in motion tends to stay in motion. Inertia. Once you get going in a direction, you tend to stay going in that direction.
Gyroscopic stabilization has been disproved
Here are a couple of articles
https://arstechnica.com/science/2011/...ns-we-thought/
https://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf
Gyroscopic stabilization has been disproved
Here are a couple of articles
https://arstechnica.com/science/2011/...ns-we-thought/
https://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf