Not Slippery When Wet

sjastro

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To determine whether tire rotation is responsible for slipperiness.

Your question seems to have developed wings because it bears very little resemblance to its original format.

Chesterton said:
Let me simplify. All other factors (velocity, weight, etc.) being equal, when the tires suddenly stop moving on a road, will the amount of friction be more, less or the same on a wet road compared to a dry one?

What you are now asking is whether rolling resistance is responsible for reducing friction.
The answer is the friction is greater when compared to the kinetic friction of locked tyres.
Rolling resistance or rolling friction depends on static friction not kinetic friction.
Static friction is higher than kinetic friction since you need to overcome inertia to set the object in motion.

There is also an engineering design to have higher friction for rotating tyres in terms of vehicle safety; it’s why tyres are made from rubber.
Tyres undergo a deformation under load which increases both the surface area of the tyre contacting the road and the static friction.
The other property is the viscoelastic nature of rubber.
Despite rubber being associated with elasticity there are many other materials that are more elastic such as metals.
Since rubber is not as elastic (=viscoelastic) a rotating tyre which undergoes compression and recovery results in hysteresis or energy loss.
This results in an uneven pressure distribution on the tyre which increases the rolling resistance and makes it safer to drive a car.
tyre.png
 
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Ponderous Curmudgeon

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Your question seems to have developed wings because it bears very little resemblance to its original format.

What you are now asking is whether rolling resistance is responsible for reducing friction.
The answer is the friction is greater when compared to the kinetic friction of locked tyres.
Rolling resistance or rolling friction depends on static friction not kinetic friction.
Static friction is higher than kinetic friction since you need to overcome inertia to set the object in motion.

Agreed, far from original but I think the real problem is Chesterton seems to be assuming that the locked tire is due to the wetness of the road when in fact that is only part of the situation.
My summary;

Friction between tire and road is decreased by the presence of water on the road due to water between the tire and the road and the shear in water layers. This is the case whether the tire is rolling or not and the main cause of "slipperiness" as we generally think of it.

Rolling friction (static friction)when the tire is rotating is greater than sliding (kinetic) friction when the tire is locked. Confusion here because static and kinetic seem to be the opposite from rolling and sliding, but the reference is to the contact patch and whether it is moving relative to the road surface contact patch.

If the forces on the tire exceed the frictional static force on the tire either due to braking or excessive power to the wheel, you shift to the kinetic mode. If due to braking, you skid and leave a black mark, if due to engine power, you have a burnout and leave rubber on the road that way. But in both cases water on the road will decrease friction further.


Finally tire design, agree, tires are elastic and designed to optimize contact patch to little pressure and patch increases in size and tire heats up and wears and reduced gas mileage increased tire wear. to much pressure and contact area goes down and safety is compromised.
 
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Chesterton

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Agreed, far from original but I think the real problem is Chesterton seems to be assuming that the locked tire is due to the wetness of the road when in fact that is only part of the situation.
Actually, I assume that the locked tire is due to the driver applying the brakes forcefully. ;)

You start your post by saying "Agreed", but then you contradict him on the point in question. He says the rolling is responsible for slipperiness, you say:
Friction between tire and road is decreased by the presence of water on the road due to water between the tire and the road and the shear in water layers. This is the case whether the tire is rolling or not and the main cause of "slipperiness" as we generally think of it.
 
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Ponderous Curmudgeon

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Actually, I assume that the locked tire is due to the driver applying the brakes forcefully. ;)

You start your post by saying "Agreed", but then you contradict him on the point in question. He says the rolling is responsible for slipperiness, you say:
Sorry, sjastro and I agree, we are trying to figure out how to explain it to you, especially considering that this thread started on a topic that had mostly different physics involved.
 
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Chesterton

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Sorry, sjastro and I agree, we are trying to figure out how to explain it to you, especially considering that this thread started on a topic that had mostly different physics involved.
No, you can't say "a" and agree with "not a" at the same time. I think you're confused. Just go back and read post #5 and then post #15 if you're interested in what was trying to be discussed. I think everything after is irrelevant.
 
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sjastro

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No, you can't say "a" and agree with "not a" at the same time. I think you're confused. Just go back and read post #5 and then post #15 if you're interested in what was trying to be discussed. I think everything after is irrelevant.
The only person confused in this thread is yourself.
Your post #8 refers to post #5 as "a great answer" yet in post #15 you try to undermine post # 5 with a red herring fallacy.
Post # 5 is based on normal driving behavior where the driver has their foot on the accelerator pedal and the tyres are rotating, not driving the car as a sled as your red herring indicates.

Even so your red herring was addressed and put to rest and your subsequent responses have indeed been irrelevant.
 
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sjastro

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The other property is the viscoelastic nature of rubber.
Despite rubber being associated with elasticity there are many other materials that are more elastic such as metals.
Since rubber is not as elastic (=viscoelastic) a rotating tyre which undergoes compression and recovery results in hysteresis or energy loss.
This results in an uneven pressure distribution on the tyre which increases the rolling resistance and makes it safer to drive a car.
tyre.png
This video makes the relationship between rolling resistance (friction) and hysteresis clearer.
 
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Chesterton

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The only person confused in this thread is yourself.
Your post #8 refers to post #5 as "a great answer" yet in post #15 you try to undermine post # 5 with a red herring fallacy.
Post # 5 is based on normal driving behavior where the driver has their foot on the accelerator pedal and the tyres are rotating, not driving the car as a sled as your red herring indicates.

Even so your red herring was addressed and put to rest and your subsequent responses have indeed been irrelevant.
Curses! You're onto me! That's right, I was not merely raising a question about something that didn't seem correct. Oh, far from it! I am actually out to get you! I so badly wanted to undermine you with a red herring, you person I don't know from Adam. Your insecurity and paranoia are well-placed.
 
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Ponderous Curmudgeon

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Curses! You're onto me! That's right, I was not merely raising a question about something that didn't seem correct. Oh, far from it! I am actually out to get you! I so badly wanted to undermine you with a red herring, you person I don't know from Adam. Your insecurity and paranoia are well-placed.
Don't go there, Both of us have been trying to answer your OP honestly, The rest of the banter was a discussion of where you might be confused and where we might have been confused by your OP and follow-ups. I learned from sjastro, and hopefully he learned from me re recognizing you actual question. Ultimately we hope that you learned as well.
 
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Chesterton

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Don't go there, Both of us have been trying to answer your OP honestly, The rest of the banter was a discussion of where you might be confused and where we might have been confused by your OP and follow-ups. I learned from sjastro, and hopefully he learned from me re recognizing you actual question. Ultimately we hope that you learned as well.
To his credit I think he probably gave the right answer to the OP. I'm not 100% sure just because I don't know how that works on the level of microns. I didn't really have any follow-ups, it was just that one point he included in the answer, that I mentioned in response to someone else. Then he kept throwing equations and formulas and charts at me (along with little insulting digs implying I'm stupid) which were not relevant to the point.
 
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Ponderous Curmudgeon

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To his credit I think he probably gave the right answer to the OP. I'm not 100% sure just because I don't know how that works on the level of microns. I didn't really have any follow-ups, it was just that one point he included in the answer, that I mentioned in response to someone else. Then he kept throwing equations and formulas and charts at me (along with little insulting digs implying I'm stupid) which were not relevant to the point.
Yes, he was correct and illustrative when we were discussing rags on the wall, but the change to tires on a wet road created confusion in that the limiting steps were different and even there, he demonstrated his knowledge well.

You are not stupid and asked a good question, but when you changed it to tires from a rag, while friction is still the answer, the generation of friction in the two cases at the level of discussion is different. The difference is not a reflection on you, but on our attempts to impart an understanding to you. Sorry if our attempts to impart understanding seem to you aggressive, but we both are trying to impart our understanding to your benefit.
 
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SelfSim

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Curses! You're onto me! That's right, I was not merely raising a question about something that didn't seem correct. Oh, far from it! I am actually out to get you! I so badly wanted to undermine you with a red herring, you person I don't know from Adam. Your insecurity and paranoia are well-placed.
This is unwarranted.
@sjastro has done a fantastic job in describing the Physics involved. Compliments are deserved .. and certainly not goading.
 
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Chesterton

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Yes, he was correct and illustrative when we were discussing rags on the wall, but the change to tires on a wet road created confusion in that the limiting steps were different and even there, he demonstrated his knowledge well.

You are not stupid and asked a good question, but when you changed it to tires from a rag, while friction is still the answer, the generation of friction in the two cases at the level of discussion is different. The difference is not a reflection on you, but on our attempts to impart an understanding to you. Sorry if our attempts to impart understanding seem to you aggressive, but we both are trying to impart our understanding to your benefit.

I didn't change it from a rag to tires. In the OP I merely gave an example of something that was slippery, although it was probably unnecessary to do so. I wish I hadn't. Then he volunteered info about tires.

You're still claiming that you and he explained it to me. Maybe I missed it. Will you please refer me to the post, or copy and paste, where it was explained that the high rotation rate of tires causes slipperiness on a wet road?
 
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Chesterton

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This is unwarranted.
No, it's warranted, and maybe overdue. I held my tongue during his condescending remarks. Then he tops it off with accusing me of trying to undermine him by raising a legitimate question. That's what people do in discussions.
@sjastro has done a fantastic job in describing the Physics involved. Compliments are deserved .. and certainly not goading.
I gave him a compliment, I told him he gave a great answer. And I gave him a Winner rating. You didn't give him a rating.
 
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Ponderous Curmudgeon

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I didn't change it from a rag to tires. In the OP I merely gave an example of something that was slippery, although it was probably unnecessary to do so. I wish I hadn't. Then he volunteered info about tires.

You're still claiming that you and he explained it to me. Maybe I missed it. Will you please refer me to the post, or copy and paste, where it was explained that the high rotation rate of tires causes slipperiness on a wet road?
At this point you are just JAQing. (just asking questions) You have been given a very significant explanation of friction re water in several disparate situations and your only answer is that we never answered your question yet at the same time, you have made no apparent effort to understand the answers you have been given.
 
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sjastro

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No, it's warranted, and maybe overdue. I held my tongue during his condescending remarks. Then he tops it off with accusing me of trying to undermine him by raising a legitimate question. That's what people do in discussions.

You also attacked @Ponderous Curmudgeon for being confused; was he also making condescending remarks or is this just a blanket excuse for justifying making personal attacks against anyone when you don't like their answers?
 
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sjastro

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Will you please refer me to the post, or copy and paste, where it was explained that the high rotation rate of tires causes slipperiness on a wet road?
Who said anything about a high rotation rate causing slipperiness on a wet road?
This is an example of you not understanding the answers given.
My answer was to use your own example as a baseline for comparison; locked tyres on a wet road.
It was explained to you rotating tyres result in an increase in friction compared to sliding tyres.

In the video I presented which compliments @Ponderous Curmudgeon answer is the patch area of the tyre in contact with the road represents a limited region of tyre tread.
A rotating tyre is therefore able to displace more water from the road where it is channeled through the tread whereas a sliding tyre can only utilize the tread in the patch area.

Both answers lead to the same conclusion a rotating tyre actually reduces the slipperiness when compared to a sliding tyre.
 
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