Split Thread The validity of classical physics (split from: DWFTTW)

[John Freestone]

No contradiction, I think, John. Usually, if I get responses that are said to contradict my claims, they turn out to be false, or apples and pears.

Oh humber, that's one of your charming little things you do again, isn't it. You're so humble. It's not that you take a lack of contention from others as reason to doubt your view; you are just right whatever happens.

Not easy to find, I agree.

Well, do keep us posted, eh, with references that support your claim. I'm clean out of ones that support mine so far, I have to admit.

You are confusing the distortion of the rubber with where the driving force is,

No, I don't think so. I'd be incredibly stupid to do that. I was describing a mechanism that might lead to the contact area being forwards of the axle, which involved considering the materials and how they would transfer force through them when a torque was applied to the wheel and resistance force applied by the road. I did not spell some of those details out quite so clearly, but I'm doing so now perfectly in accord with what I did indicate earlier at first intuitive glance. I try also to do the same and get your result, but my mind revolts.

and you need to drive it from the axle not the rim.

I think I understand what you're saying here, that in the case of the driven wheel, the torque is transfered to the wheel via its axle, but I did not imagine anything different from that. Then the wheel, forced to begin turning, transfers that force to the ground (I suppose roughly linearly, backwards), which resists if there is friction (applied force forwards), which causes (in my imagination, at least) the rubber or whatever to bunch up to the fore.

I assume, of course, that you mean that the contact area includes the position directly below the axle, but extends more to the rear? We haven't got daylight between that axle position and the tarmac, surely? ...oh, you define it later as at the edge....wow!...

Tyres are complex, and have controlled modes of flexure, because they must also handle cornering forces etc.
(As an side, an engineer told me that marketing would often reject tyre designs, because they did no look 'aggressive enough'. I found that disquieting.)

Yeah.

ETA: The forward distortion that you see in soft rubber is the 'plough' of the rear acting force.

This sounds rather like what I'm describing, but where these terms 'plough' and 'rear acting force' come from, I don't know. I interpret it as I said - the resistance of the road through friction (rear acting force? - but it's directed forward in my case) causes the distortion I see in soft rubber. It is compressed by the torque trying to force it down at the front against the ground, which (even temporarily) resists that force.

Think of a car in soft and or mud. A belt moving belt under the wheels cannot do that, without moving the cart along with it, let alone create a force from the rear, to be in the opposite direction.

If your wheel has sticky surface, and you roll it over a sheet of paper, then the paper will shear a way from the rear.

Non grokki mio das relevienza. (I just made that up)

The car is in forward motion, so the driving force must come as thrust from behind the driving axle. The contact patch, the reactive frictional force of the ground, must also be from behind the axle.
It is not possible for for the wheel to drag the vehicle forward in front of the axle,

This is your most impressive point, I think, the idea that the wheel can only be pushed by the ground, and not pulled. I sense that it isn't actually true, however, and you let the cat out of the bag already with that sticky shearing sheet of paper earlier. Did that get pushed from behind too? No, it is quite easy to refute what I think your argument is here: if you have a wheel in an even more extreme negation of this than I am suggesting, when it's trying to mount a curb, for instance. It still makes darn good progress up the curb (or just a sharp incline while the rear wheels are on the level). It doesn't have to have a contact point behind the axle to do that. It can drag itself up. Friction is a wonderful thing, as you know.

because the first point of contact lies directly under the axle.

Mere assertion as cause of the above idea, which I seem to have now refuted. But wait: on slightly flat tyres going slowly? You must have seen contact points spread widely either side of the axle.

That is why the wheel must deform to some degree for driven motion to occur.

A further effect of the cause "the first point of contact lies directly under the axle", not established.

The only option for forward motion, is behind the axle.

Repetition of your assertion. C'mon, you're just making this all up, incha?

This is also why locomotives can pull more than their weight. The static friction of the driving wheels against steel is low and due to gravity, and lying under the axle. Force of acceleration distorts the wheel and track to produce a higher rolling friction, allowing greater loads to be hauled, because the hauled wheels will still have something like the lower static friction.
Early railway engineers did not know this, and built geared tracks and even legs. (Brunton's and Blackinson's engines.)
There, something that has been learned about classical mechanics in the last 200 years.

That looks like an interesting tangent. Thanks.

Which side of the axle do you reckon the contact point tends towards when you do an emergency stop? We might be able to feed that bit of intuition/memory/whatever into our musings.

 

[Furcifer]

Of course we don't agree. We realize that propellers cannot create mass out of nothing. It's not even worth offering a reference.



I assure you the ignorance is all yours. I'm confident that anyone on this forum (with the possible exception of humber) will be happy to confirm this.



I never cease to be amazed at the irony that comes from the ignorant.



And I simply pointed out that you were (and ARE) wrong.



No - in fact you've made up some very entertaining explanations already.



It's important to distinguish between your inability to understand and our inability to explain. Plenty of others have grasped it - only because they were willing and interested. Not because they could decipher our inscrutible analyses.



You really shouln't let this thread cut into the important business of your life. We'll understand if you have to stop insulting us here.



But you have no problem taking a condescending attitude with people such as myself with an M.S. and many years of experience in aero.



Pure B.S. But thanks for playing.

See arrogant, ignorant and obnoxious to the end, at least you're consistent.

I have no doubt you're an engineer

Way to contribute. Thanks for...nothing!

 

[humber]

The thrust from the wind has to translate into a linear motion. The distance the the tip of the prop travels in one rotation at a given windspeed is greater than the windspeed relative to the road. The shaft translates this into linear motion in the wheels. I guess as long as the losse aren't too great, the wheels travel further forward than the wind in the same amount of time due to the area swept out by the prop.

If the power is available, increased acceleration may be achieved by this means, but not final velocity. The wheels and geared prop acting some thing like a governor.

 

[semper]

If the power is available, increased acceleration may be achieved by this means, but not final velocity. The wheels and geared prop acting some thing like a governor.

I vote that neither Humber nor 3body have any idea how propellers, wheels, and treadmills work, and therefore are unlikely to ever understand how a wheel and propeller wind interface vehicle on a treadmill can work, no matter what classical physics is applied.

Any seconders?

 

[humber]

Oh humber, that's one of your charming little things you do again, isn't it. You're so humble. It's not that you take a lack of contention from others as reason to doubt your view; you are just right whatever happens.

I think making humility an asset, is conceit.

Well, do keep us posted, eh, with references that support your claim. I'm clean out of ones that support mine so far, I have to admit.

There is no need. It is simple to comprehend. If you want details, then you can find them.

No, I don't think so. I'd be incredibly stupid to do that. I was describing a mechanism that might lead to the contact area being forwards of the axle, which involved considering the materials and how they would transfer force through them when a torque was applied to the wheel and resistance force applied by the road. I did not spell some of those details out quite so clearly, but I'm doing so now perfectly in accord with what I did indicate earlier at first intuitive glance. I try also to do the same and get your result, but my mind revolts.

I think I understand what you're saying here, that in the case of the driven wheel, the torque is transfered to the wheel via its axle, but I did not imagine anything different from that. Then the wheel, forced to begin turning, transfers that force to the ground (I suppose roughly linearly, backwards), which resists if there is friction (applied force forwards), which causes (in my imagination, at least) the rubber or whatever to bunch up to the fore.

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.

I assume, of course, that you mean that the contact area includes the position directly below the axle, but extends more to the rear? We haven't got daylight between that axle position and the tarmac, surely? ...oh, you define it later as at the edge....wow!...

Caught up in your own dissimulation there, John.

Yeah.

Yes, things are not always what they seem. Including tyre 'advances'

This sounds rather like what I'm describing, but where these terms 'plough' and 'rear acting force' come from, I don't know. I interpret it as I said - the resistance of the road through friction (rear acting force? - but it's directed forward in my case) causes the distortion I see in soft rubber. It is compressed by the torque trying to force it down at the front against the ground, which (even temporarily) resists that force.

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. 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.
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. 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. 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.

This is your most impressive point.

The ladies think so.

I think, the idea that the wheel can only be pushed by the ground, and not pulled. I sense that it isn't actually true, however, and you let the cat out of the bag already with that sticky shearing sheet of paper earlier. Did that get pushed from behind too? No, it is quite easy to refute what I think your argument is here: if you have a wheel in an even more extreme negation of this than I am suggesting, when it's trying to mount a curb, for instance. It still makes darn good progress up the curb (or just a sharp incline while the rear wheels are on the level). It doesn't have to have a contact point behind the axle to do that. It can drag itself up. Friction is a wonderful thing, as you know.

The wheel does not climb the curb by clawing its way up. In the case of a rear wheel drive, obviously not. That is also a complex action, and not the same as a cart on a belt.

Mere assertion as cause of the above idea, which I seem to have now refuted. But wait: on slightly flat tyres going slowly? You must have seen contact points spread widely either side of the axle.

I have seen flat tyres. I do not falsely generalize about wheels from them.

A further effect of the cause "the first point of contact lies directly under the axle", not established.

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.

Which side of the axle do you reckon the contact point tends towards when you do an emergency stop? We might be able to feed that bit of intuition/memory/whatever into our musings.

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.

 

[humber]

I vote that neither Humber nor 3body have any idea how propellers, wheels, and treadmills work, and therefore are unlikely to ever understand how a wheel and propeller wind interface vehicle on a treadmill can work, no matter what classical physics is applied.

Any seconders?

So far. No evidence that you understand how a belt drives a wheel, the idea of power transfer..., just the usual catch-cry, again.

Try this:
A runner on a treadmill largely exercises locally. The limbs do work against gravity, but the runner does not gain KE due to linear velocity as on the road. This difference is probably not important to the matter of exercising, so a belt is adequate simulation.

A runner standing on the belt, so as to go back with it, will have KE due to his velocity w.r.t the ground. A ground observer would confirm this.
If the runner runs up against the belt, he will arrive at beltspeed with zero velocity w.r.t the ground. A ground observer will agree with this.
However, there also is no KE w.r.t the belt. The runner had KE when moving with the belt, which was returned to the motor as progress was made up the belt (via reaction of the feet to the belt, so pushing the belt in the driven direction). This may not happen is practice, but does so in principle. This would be so in the case of a runner on a static belt, while accelerating a dummy (load) mass. The presence of the motor does not preclude that exchange.

Note that the treadmill has some validity when used this way (though not an equivalent of the real road) but looses it completely in the case of a cart simply placed at windspeed. This is like a runner stepping on the belt by suspending himself from the bars, and lowering his feet running, as it were.
In this case, he still has no KE, nor could have gained it, but the process of doing so, the work required, is avoided.

The cart cannot travel up the belt like the runner. It remains at windspeed, something like a runner on the spot, using minimal energy.

 

[humb]

Well!

A few days away from the interwebs spent in another frustrating chiropterid skirmish, and look at the fine mess I return to! I'm pleased to see that my absence has caused no problems, and that I am, in fact, superfluous for now. It's quite comforting to see others knowledgeable in the Truths of Physics and the Whereupon. It's truly fine to finally read some sensible discourse on this forum, of the truths of wheel distortion, the obvious facts of mass increasing when it passes through a propeller, and the illumination of treadmill resonance as an energy multiplier. The age of the liberals is upon us! Down with conservation!

As for you, spork, what exactly is it that makes you believe that you haven't dropped acid this week? Wouldn't you agree that indications appear to be to the contrary?

 

[Furcifer]

I vote that neither Humber nor 3body have any idea how propellers, wheels, and treadmills work, and therefore are unlikely to ever understand how a wheel and propeller wind interface vehicle on a treadmill can work, no matter what classical physics is applied.

Any seconders?

Lol, what is so hard to understand. The cart gets pushed to windspeed, prop or no prop. With a prop, at wind speed, you have a diffential, the standing air in front of the prop accelerated by the prop producing thrust.

I'm astonished at the lack of knowledge on gradients here. Well not really, too many engineers

 

[ThinAirDesigns]

I vote that neither Humber nor 3body have any idea how propellers, wheels, and treadmills work, and therefore are unlikely to ever understand how a wheel and propeller wind interface vehicle on a treadmill can work, no matter what classical physics is applied.

Any seconders?

Seconded in a heart beat.

JB

 

[humber]

Seconded in a heart beat.

JB

An action of the autonomous nervous system.

 

[Furcifer]

Well!

A few days away from the interwebs spent in another frustrating chiropterid skirmish, and look at the fine mess I return to! I'm pleased to see that my absence has caused no problems, and that I am, in fact, superfluous for now. It's quite comforting to see others knowledgeable in the Truths of Physics and the Whereupon. It's truly fine to finally read some sensible discourse on this forum, of the truths of wheel distortion, the obvious facts of mass increasing when it passes through a propeller, and the illumination of treadmill resonance as an energy multiplier. The age of the liberals is upon us! Down with conservation!

As for you, spork, what exactly is it that makes you believe that you haven't dropped acid this week? Wouldn't you agree that indications appear to be to the contrary?

Oh, you just missed spork unveiling his "Principia Cartica".

Just kidding. He's waiting for everyone else to do the work for him.

I joke, I joke. We're buddies. He loves this stuff.

 

[spork]

I'm astonished at the lack of knowledge on gradients here.

And we're astonished at your lack of understanding of all things physics and common sense. Add to that your condescending and abrasive attitude and you've got quite the package.

 

[Furcifer]

a wheel and propeller wind interface vehicle on a treadmill can work, no matter what classical physics is applied.

Lol, is this supposed to make you look smarter while your talking trash?

sorry, let me rephrase that

Oh my! Is this an attempt to discretely coverup your own lack of knowledge while you passive agressively attack my intelligence?

 

[ThinAirDesigns]

I'm astonished at the lack of knowledge on gradients here.

Well, as a 3000+ hour soaring pilot (with 2 gliding National Championships and a World Championship to boot), please impart some knowledge regarding wind gradients. I'm all ears.

JB

PS: I'm sure hoping your gradient knowledge is better than your prop knowledge or trouble brews.

 

[ThinAirDesigns]

Semper:

... wheel and propeller wind interface vehicle ...

Lol, is this supposed to make you look smarter while your talking trash?

sorry, let me rephrase that

Oh my! Is this an attempt to discretely coverup your own lack of knowledge while you passive agressively attack my intelligence?

Do you have something *against* a wheel and propeller wind interface vehicle?

JB

 

[spork]

Well, as a 3000+ hour soaring pilot (with 2 gliding National Championships and a World Championship to boot), please impart some knowledge regarding wind gradients. I'm all ears.

I can't wait for his primer on gradients. If it's half as good as humber's explanations it'll all be worth it.

I'm betting it'll involve hopping, resonance, energy multipliers, heterodynes, and coriolis... and maybe negative drag.

 

[Furcifer]

And we're astonished at your lack of understanding of all things physics and common sense. Add to that your condescending and abrasive attitude and you've got quite the package.

Um just so you know, all you've done is present strawmen and avoid making any contribution to the conversation.

 

[Dan O.]

Dan, do we need to start a separate list, or can we just lump this lump in with humber?

I think 3bodyproblem is just vying for attention. He should probably be reported for the personal attacks and put on ignore. Humber is enough entertainment for this thread.

 

[humber]

Well, as a 3000+ hour soaring pilot (with 2 gliding National Championships and a World Championship to boot), please impart some knowledge regarding wind gradients. I'm all ears.

JB

PS: I'm sure hoping your gradient knowledge is better than your prop knowledge or trouble brews.

pd = dynamic pressure (Pa)

pd = 1/2 ρ v2

ρ = density of fluid (kg/m3)v = velocity (m/s)

 

[humber]

I can't wait for his primer on gradients. If it's half as good as humber's explanations it'll all be worth it.

If yours were twice as good, they would still be half-baked.

I'm betting it'll involve hopping, resonance, energy multipliers, heterodynes, and coriolis... and maybe negative drag.

And many other things you don't understand