Engineer Physisist question
 

I ride a bicycle. I know it is easier to keep from falling over the faster I am going.

Why?

Law of conservation of angular momentum.
You have several gyroscopic stabilization devices on your bicycle.

This.

fear..........

Read: http://mitpress.mit.edu/books/bicycling-science

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.

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.

Magic? ;)

[url="http://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.

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.

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.

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.

The physical forces of a bike without a rider are not the same as a bike with a rider. The answer to the OP's question is not unknown, it is simply a lot more complicated than most folks are going to be able to understand because of the mathematics. The simplistic models concerning two areas; riders ability to balance and the gyroscopic effect are the easiest explanations (but not the most complete) of the two primary forces involved.

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.

because someplace half way across the world a butterfly flapped its wings and it created a sequence of natural events that ended up in a small vortex of swirling wind around you pushing equally from every side keeping you upright.

only assuming you are on a flat surface in near perfect conditions and the person pushing it has done it perfectly so as not to exude balance in any directions except straight forward. otherwise the thing could fall over after 3 feet.
i thought this is common knowledge.

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.

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.

The gyro effect does a lot to keep you upright; it's one reason trackstanding is tougher than a slow-rolling intersection approach -- when trackstanding, there's NO gyro effect.

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...!

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.

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.

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.

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:

http://janheine.wordpress.com/2011/0...orks-together/

Nice answer - 10/10

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

http://arstechnica.com/science/2011/...ns-we-thought/

http://www.phys.lsu.edu/faculty/gonz...9no9p51_56.pdf

Tests like this always bother me, because a counter rotating wheel will not decrease gyroscopic force. That wheel's gyroscopic force will just be added to the force created by the first two wheels.