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Discussion in 'The Perfect Line and Other Riding Myths' started by garandman, May 27, 2011.
That's not a violation of the 3rd law. Why should it prevent that from happening?
Of course it isn't a violation of the Third Law. You stated:
This was error.
No it wasn't. If the bike is falling over due to gravity, you can hasten or delay the impact of the bike on the pavement by shifting your weight one way or another.
If you ride the bike out of the back of a flying cargo plane, while in free fall, if you lean the bike one way, your body will move in the other. There's no difference because you're falling.
Oh, I quite agree. The problem is, you have stated that to delay said impact of a bike which is falling to the left, you should move your body farther to the left. This is an absurdity.
No it isn't, it's a fact. It doesn't change the center of gravity of the bike+rider system, but it would delay the point at which the bike part of the system hits the pavement.
Ever taken any analytical mechanics courses? Just curious.
Let's assume you're correct. Wouldn't it be better to shift your weight to the right and avoid falling altogether?
Motorcyclists and bicyclists with exceptional balance can remain stationary on two wheels indefinitely by shifting their weight right and left of center. It is never the case that a cyclist arrests a fall in a particular direction by shifting their weight farther in that direction.
Pointing out that a person could do such is a thought exercise to illuminate a principle of motion. The objective is to understand the physics, not promote a riding technique.
People who can balance two-wheelers while stationary depend on the fact that the point of contact with the ground is not a point contact but a surface of non-zero area that provides some tipping resistance. This phenomena is irrelevant to our discussion.
It still works exactly the same.
It's just called Contra-steering.
Best first post!
You're making yourself dizzy.
In your theoretical example on a stationary bike that's perfectly balanced. If you shift your torso to the left the bike will shift to the right and you should remain balanced. equal and opposite reactions. Ignoring for the moment the resistance of the tires, air, etc.
Try this. sit in a chair with casters on a hard wood floor. Lift your feet off the floor and shift your torso to the left, what happens? The chair moves to the right. The same forces that move the chair, move the bike as well.
As for this:
I totally agree with you. So why does leaning to the left cause the handlebars to turn to the right?
I can do that trick. We sprinters call it a "track stand." Countersteering principles are applied. The front wheel is cranked a bit to one side, and the bike moves forward and back just enough to keep the contact patches under the rider's center of gravity. Going forward and back is done with a fixed gear, or by using an uphill, or the crown/slope of the pavement. There's mention of the contact patches being a non-zero area in another post, but wee 18mm track tires at 150 psi are darn close to point contact.
The hard part of the skill for most is learning to let the bike go backwards.
I presume the same can be done with a moto by abusing the clutch. Haven't tried yet.
Forgive the slow response. Happily, I still have a job.
I'm not sure what you mean by a bike that's "perfectly balanced." I'm talking about a motorcycle being actively balanced by a rider at a complete stop. If that rider is me, it will eventually fall over on one side or the other. It will fall to the side on which the greater weight preponderates. We are at a point now where you and Klay will not acknowledge that the motorcycle will fall in the direction of the greater weight. You will next assert that a tightrope walker in danger of falling off the rope to the left will tilt their balancing pole farther to the left to keep from falling.
I'm sitting on a rather ordinary HON Company faux leather swiveling office chair with five casters. I don't have a hardwood floor at my disposal, but the chair is on a smooth plastic mat. The chair did not move in any direction, although I was able to get it to swivel left by twisting my torso to the left and vice-versa.
As for this:
Because the handlebars can turn, they must, if force is applied. This is no different than if I pushed the handlebar with my hand.
You can't ignore what our world is made of. Friction, resistance, weight, gravity, and so on...we're talking about a motorcycle here, not an astronaut "walking" in the outer space.
There is no "direction of greater weight," if the bike is balanced on the contact patches. Once it goes off center for some reason, it'll fall over. Why in the world are you struggling with these simple concepts?
That's exactly what a tightrope walker would do. The opposite and equal force keeps the walker upright.
He is simply missing the points of movement within the system. There are two points. The external point being the tyres to the road and this is able to provide the unbalanced force. The internal point being basically the hips of the rider. If the point above the hips has a mass of say 60kg and the centre of that mass is moved say 10cm to the right then if the point below the hips has a mass of say 120kg the centre of mass of that part would have to move 5cm to the left. The equilibrium of the system is maintained.
Why complicate the matter by adding in other variables. He won't even recognize what it means to have an equal and opposite reaction to a force.
If your hands aren't on the handlebars, what force is being applied to the bars when you shift your torso to the left?
In your chair, if you turn your upper body left, the chair turns to the right, unless you are pushing with your feet or your hands etc.
If you were on a hard wood floor, and moved your torso fast enough to overcome the friction of the wheels, the chair moves opposite the direction your torso. That's the definition of equal and opposite.
Like then you shoot a rifle and it kicks you in the shoulder. You impart forward motion to the bullet and backward motion to the rifle. Equal and opposite.
You can't move in one direction without pushing on something in the opposite direction.
Yeah, it's why the bullet travels 1 mile away but your shoulder just 1 inch backward...
It's not because the forces are equal that the results are. Equal and opposite the results would be without inertia, weight, resistance, friction, blah blah blah. You can't ignore them.
I don't particulary like when someone uses pure theorical concepts to explain real life phenomena, sorry. At the end it serves no goal but showing your own knowledge (or lack of).
It's not a science competition guys...we are on a damn motorcycle forum after all. What is important here? The result or the theorical concepts and applied forces?
Me think it's the result...but I can be wrong.
Equal and opposite. Momentum is mass times velocity. An equal amount is imparted to both the bullet and the shoulder. The bullet is very light compared to the body, but moving much faster. The shoulder moves slower than the bullet, but has much more mass. Equal momentum is imparted to the shoulder and the bullet.
I get the equal and opposite force but what would happen if the chair didn't have wheels? If you move your torso would the chair move? I think not. Since motorcycle tires do not slide sideways very easily, wouldn't a chair without wheels be a better example?