Are you sitting comfortably?
I think making humility an asset, is conceit.
A lack of humility, expressed as you demonstrated here in thinking yourself right irrespective of any response from others, means you have a tighly closed mind, resisting any view that isn't already yours. Feigned or over-exaggerated humility can be a conceit, I grant you. People can also genuinely believe themselves to be very humble, while that confidence in their "asset" is a self-conceit. But those are like double-negatives; disregarding humility
is just conceit, vain pride, arrogance, too great a confidence in one's knowledge or abilities. As any extensive dictionary should tell you, humility and conceit are to be found as antonyms: once again you seem to have something in direct opposition to how almost everyone else agrees it is. You seem actually to be quite sophisticated and deep in some respects, but this sophistication seems to cause you to mistrust the "bleedin' obvious" over and over again, as if you made a decision at some point that reality is always the opposite of what it seems.
What is the point in discussion unless each side accepts that they may learn from the other, change their mind, and practice just a modicum of humility by that? Discussion with you, if you consider yourself always right, must be mere absorption of instruction from your great wisdom, and all dispute in vain.
There is no need. It is simple to comprehend. If you want details, then you can find them.
I really thought we might discuss, put our theories forward, and learn from other people who have posted information on the net, together, as a shared educational experience. After being wrong before, I was trying not to be arrogant, and just accept that we had different views and whatever the truth turned out to be, well, ok. But clearly you aren't interested either in what I think or what anyone else has thought, discovered, theorised or proved anywhere else!
Yet you've said several times that wheel motion is very tricky. So again, this demonstrates your conceit. Wheels, like every other subject we touch on, is much more complicated and subtle than anyone else could possibly understand, but you don't need to check anything out with anyone else, do empirical testing, or think further on the subject. I guess you must have been born knowing everything.
That is a reaction not to the applied force, (the wheel is undistorted if raised from the ground) but the opposing force of the ground; the reaction to it. The described effect, means that the force is from the rear, so the frictional force, that in opposition to driving force, is from the rear. It must be.
That is what I said, the frictional force from the road is from the rear. You are ambiguous there, however. There is the other force, that from the wheel, which is from the front. First year physics, I'm fairly confident, will explain this: a wheel drives by "pushing" backwards against the ground, basically, and the friction of the ground "pushes" back. Now, while "pushing" might give you confidence that the wheel's contact position must therefore be rearwards of the axle (from the principle that we can't push a rope), it is wise to be cautious about that. Friction, as we all know, has some kind of stickiness about it, and we know that we can pull things with an adhesive surface, no push required. We can sit on a wheeled trolley on a flat surface, put out our hands and pull ourselves forward with just the friction of our hands on the surface, well in front of our bulk and centrre of mass.
Caught up in your own dissimulation there, John.
No, just trying to clarify our shared understanding of the question, a requirement for us to comprehend each other's answers.
Plough is a term you will find in use.
For a soft wheel, that must happen. In a solid wheel, it is not visible, but the wheel must be compressed as you say.
Ok. Good. Something we agree on. I would say that a completely solid, non-deformable wheel is an ideal, a mathematical abstraction, but that there is a gradation from soft objects through to very hard ones. We haven't considered the surface, except in your suggestion of soft sand, but I didn't understand what you were trying to say. The mathematical ideal is very informative, actually. If a wheel and the surface did not deform at all, the contact point would be one of those odd things in maths, a kind of zero that isn't zero, an infintessimally small location, a point (or line if we give it the sideways dimension). Whether such a wheel could be driven is almost into the realms of philosophy, depending on whether you arbitrarily decide that forces can be transmitted (particularly frictional forces, laterally!) via an "area with one dimension infintessimally small or zero", a "contact line with no width", or however we conceive it. What is clear is that as we approach the "ideal" (in the sense of "in the mind") the usefulness for locomotion becomes less than "ideal". As a rough rule of thumb, I'd say that being deformed at the contact surface is part of how wheels work; without being somewhat elastic they would just spin; with a point contact in the limit, no friction can exist.
That is then perhaps the "driving' plough, that is the result of reaction to the 'bit of tyre stuck to the road' further back and behind the axle.
Perhaps? Is that your conceit talking? If there was a "driving plough", I'm not sure what it is. Let me assume it is a compressed area, since you say it is further back, and imply, I think, that its presence pushes the wheel forward. But you say that it is the bit of tyre stuck to the road further back. If we take friction literally as a stickiness, then the contact patch behind the wheel would slow it, as the rubber was peeled off the road. It takes a lot of energy to unstick sticky things. But more importantly, if there is a compression of material behind the wheel axle position, I don't see how it can be sustained: that part of the tyre is being pulled away from the road.
It does not really matter if you disagree with the direction or location of the force applied by the wheel to the road. You can simply generalise. The frictional forces will be opposite to that of motion.
Well, that's all rather confusing. The "frictional force", if by that we mean what the road applies to the tyre, will be with the direction of motion, not against it. But we might (I would say
should) consider two opposite forces when something acts in this way, as per Newton's 3rd: the tyre applies a frictional force to the ground against the direction of motion. The bottom of a wheel doesn't exactly go backwards (or may slighly perhaps), but it has to be pushing backwards for the wheel to move forwards, just as a fish must push water backwards to move forwards or your feet must push backwards on the ground when you walk forwards (the usual way). These two opposing forces cause relative motion between wheel and ground.
It is not possible for a belt (the actual driving force) to drive the wheel in such a way as to produce a reactive force to directly drive the axle in the opposite direction , let alone exceed it.
I think that's right, although you have of course reversed the condition from driven wheels to driven surface, and specified a cart on a belt, where I thought we were just discussing wheels, but no matter.
A simple cart will go back with the belt for this reason. However, the wheel can drive the propellor, and that can make the small amount of force required to keep it in place, but that is all.
You're obsessed, man! First understand wheels, then get back to the cart on a treadmill.
I'm sorry to hear that.
The wheel does not climb the curb by clawing its way up.
Well it does a very good impression of a wheel clawing its way up a curb.
In the case of a rear wheel drive, obviously not.
It makes no difference if it's a real wheel or a front wheel or a wheel in the middle of a six-wheeler. If it's about 2 feet high and meets a 4" curb, is driven, and climbs the curb slowly enough not to be bounced up by the vehicle's momentum, then the kerb first touches the tyre well forward of the axle, and the wheel then continues to make its way up somehow. Of course, you might have argued that you are defining the axle position as falling on a line drawn from the centre of the axle towards whatever we consider the "gradient" of the ground, rather than the vertical, but the nearest you get to that argument is to say:
That is also a complex action, and not the same as a cart on a belt.
Missed opportunity, and wrong anyway. Climbing, the contact patch would move even further forward/upward due to the weight of the vehicle, where on the level it is the inertia and aero drag. But you're right, it is a complex problem when you get into the details. Introducing gradients and obstacles, as I did, makes dealing with gravity necessary if we analysed it more closely. Let's not.
I have seen flat tyres. I do not falsely generalize about wheels from them.
No, perhaps not, but here is the point. When you're running on a flat, obviously (I hope) the axle position lies within the contact area. There is also obviously a continuum from that to something approximating a circle as we pump the tyre up. We know that we can drive forward on a flat, but you seem to suggest that normally a wheel has a contact area bounded at its front edge by the axle position. It seems to me therefore, that there must be a point at which a tyre is sufficiently inflated for the wheel to work
as you say a wheel works, yet you also admit that
a wheel works without that condition being present. Do you understand basic logic? The ability to drive on a flat tyre defeats your argument that the contact area must be behind and bounded by the axle position.
It's a circle, how else? That is the case if there is no consequent distortion; the result of reaction to a force from the rear. That cannot happen if it must originate to the front of that no load point, and therefore the axle, otherwise the wheel would need to be where it is intending to go.
I don't understand any of that, but what wheel is circular?
Must be generally to the front, and slave wheels are involved. Braking is different, because efficient motion is not the aim, just loss, so scrubbing and dragging play their part, as does avoiding melting.
Well it's time to get your rubber pencil eraser out again. Holding it tight in your hand will simulate a tyre on a wheel with the brakes on full. That would be unwise for a proper emergency stop, but it's the extreme case to start with. Rub it along your desk, and you'll find that its contact area is pulled to the rear of the motion. A wheel does the same thing and, with some rotation of the wheel instead of brakes locked, that force is still in the same direction, causes the same kind of distortion of the tyre, but reduces it. Even if we skid, the same is true.
Your vision is almost of a tyre that has to jump ahead of the wheel to provide a push force against the wheel...or you just realise that you have to say that, because we can reverse these motions and prove the first case wrong by it, which was why I asked the question, as you will already realise. You would by changing frames of reference, of course, see that braking and accelerating are (almost?/absolutely?) identical-but-opposite conditions: the momentum of a car requires that motion can't just disappear, the relative motion of ground and tyre can be thought of as the ground trying to apply a torque to the wheel, backwards at the bottom, but resisted by the wheel, hence the tyre will bunch up behind the axle position just as your eraser does on the desk. How could it jump - or the road suck it to a position - further forward of where the axle has got to?
