Not Slippery When Wet

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
I did address your question; perhaps the issue here is you didn’t understand the answer.
You cannot treat a skidding car with its wheels locked as a separate or isolated issue without considering the initial conditions which occur prior to slamming on the brakes.

For argument sake let’s assume the car does skid when the brakes are applied.
On a level road before applying the brakes there are three forces acting on the car which affects its forward motion.

f₁ = ma the forward acceleration where m is the mass of the car and ‘a’ is the acceleration.
f₂ = kvⁿ the air resistance where k is a constant and n and is a positive integer.
f₃ = μN the frictional force where μ is the coefficient of friction and N = -mg where N is the reaction force and g the acceleration due to gravity.

f₂ and f₃ act in the opposite direction to f₁.

ΣF = f₁ + f₂ + f₃

If ΣF > 0 the car is accelerating and if ΣF = 0 the car is moving at a constant velocity.

When the brakes are applied there is a decelerating force or an impulse which is applied for period of time t which changes the momentum of the car.
At the end of the impulse period there is now only one force f₃ acting on the car as f₁ = 0 since the car is moving under its own inertia and f₂ ≈ 0 since the velocity becomes relatively small.
The car eventually comes to a stop as the frictional force f₃ overcomes the inertia.

The point here is it confirms the frictional nature of water when it is modelled as a composition of layers which needs to be overcome, the car moving due to inertia where the wheels are locked does not overcome the internal friction of the water layers.
Are you sure you are not just modelling hydroplaning? Wet traction in a car is due to reduced contact patch between tire and road due to inability to clear water from the actual tread in contact with the road, contact decreases as the speed increases due to an inability to remove increasing volumes of water, in the extreme where there is a layer of water across the entire contact area you reach a limit where the water shear becomes relevant and you are now hydroplaning. beyond that, there is the difference between static friction and rolling friction if you actually stop the tire from rotating.
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,911
3,964
✟276,869.00
Faith
Christian
Marital Status
Single
Are you sure you are not just modelling hydroplaning?
That's exactly what l have done.
In this thread I have only considered layers of water existing between the surfaces whether it be between a towel and table benchtop or between car tyres and the road surface.
The situation of a car sliding across a wet surface where the tyres are not rotating is substituting rolling friction with kinetic friction in which case I believe hydroplaning is an adequate description.
 
Upvote 0

Chesterton

Whats So Funny bout Peace Love and Understanding
Site Supporter
May 24, 2008
23,815
20,224
Flatland
✟865,803.00
Faith
Eastern Orthodox
Marital Status
Single
I did address your question; perhaps the issue here is you didn’t understand the answer.
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?
 
Upvote 0

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
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?
I don't exactly either. Partly because skidding and hydroplaning are two different situations. the resistance to motion is dependent on the area in contact between the tire and the road surface. This decreases as the amount of water between the tire and the road increases and eventually reaches the point where there is a complete layer of water between the tire and the road and at that point the only resistive force is the shear component of the water layer and we have hydro or aqua planing.

But to go back to the original question, I think sjastro it correct that it has to do with wetting and hydrophobicity, or surface energy, depending on the surface, adding water to the towel will increase the wetting and hence adhesion area of the damp towel. Try it with a damp sponge on several surfaces and you will find differing friction coefficients between dry and damp sponges and different materials.

Thus I think you can hang a damp towel better than a dry one so long as the advantage of the adhesion of the water is sufficient to hold it better than a dry one and the excess weight of the water does not pull you into a realm where it is only the water shear that is resisting movement.
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,911
3,964
✟276,869.00
Faith
Christian
Marital Status
Single
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?
The friction will be less because the coefficient of friction μ for the wet surface is reduced.
There are extensive studies of this from a road safety perspective.

friction.jpg
https://pdfs.semanticscholar.org/91b4/7503b1cd58fcbc57b66c62425407a660d8f6.pdf
 
Upvote 0

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
The friction will be less because the coefficient of friction μ for the wet surface is reduced.
There are extensive studies of this from a road safety perspective.

friction.jpg
https://pdfs.semanticscholar.org/91b4/7503b1cd58fcbc57b66c62425407a660d8f6.pdf
Yes and the reason for this is a reduced contact patch between the tire surface and the road surface. If this were not the case, then there would be no difference due to tread depth and in fact slick or bald tires with no tread would be the best as they have maximal surface area.
 
  • Agree
Reactions: Ophiolite
Upvote 0

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
There you go.
I have a damp towel hanging off my counter. (I was cleaning anyway) I will see if it is still hanging tomorrow. BTW, 80/20 seems to be about the max.
 
  • Like
Reactions: Chesterton
Upvote 0

SelfSim

A non "-ist"
Jun 23, 2014
6,174
1,965
✟176,444.00
Faith
Humanist
Marital Status
Private
As I find weirdness fascinating, I've been watching some YouTubes called 'Off Road Rescue'. The main character in it believes that he is able to rescue other vehicles stuck in either mud or dry sand, with his specially designed fuel guzzling monster, because his bigger tires give him more buoyancy.

That seems like it might be a factor in his case, given that in just about every 'rescue', he absolutely flaws his huge capacity V8 motor, causing his big wheels to instantly spin. He made the statement that he has about the same 'grip' as the vehicle being towed but his extra buoyancy, created by his bigger tires, gives him the advantage.

In one episode, he deflated the tires of the stuck vehicle, which he then claimed as allowing him to then be able to remove it from the mud, but the other vehicle's motor was not even being used!?
 
Upvote 0
This site stays free and accessible to all because of donations from people like you.
Consider making a one-time or monthly donation. We appreciate your support!
- Dan Doughty and Team Christian Forums

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
As I find weirdness fascinating, I've been watching some YouTubes called 'Off Road Rescue'. The main character in it believes that he is able to rescue other vehicles stuck in either mud or dry sand, with his specially designed fuel guzzling monster, because his bigger tires give him more buoyancy.

That seems like it might be a factor in his case, given that in just about every 'rescue', he absolutely flaws his huge capacity V8 motor, causing his big wheels to instantly spin. He made the statement that he has about the same 'grip' as the vehicle being towed but his extra buoyancy, created by his bigger tires, gives him the advantage.

In one episode, he deflated the tires of the stuck vehicle, which he then claimed as allowing him to then be able to remove it from the mud, but the other vehicle's motor was not even being used!?
I'd laugh immediately except in my weirdness search, I saw a video of a mud buggy in iceland that travelled across water by having large tires with even larger treads that effectively turned them into paddlewheels. But as they said it was not the buoyancy that made it possible as the craft would sink if they did not keep up speed.. I rather think that your example is confusing the large surface area of tread and tire that allows him to ride on the surface as in the video I saw last night. See Hydroplane boat just to add more confusion to our discussion.

On another note, deflating the tires on your own vehicle will increase traction and is commonly done in sandy conditions, it increases the contact area with the sand. I can't see it would help with the towed vehicle.

And finally yes, the big V8 helps in that he can use his tires to dig through the surface till he finds purchase and then by applying multiple bursts of increased traction can pull the tiny car out of the mud. On the other hand, any normal tow truck driver will set his vehicle so that it won't slide and use the little electric winch on the back to do the actual work without wasting hundreds of dollars in tires. Real tow truck drivers use physics.

I live on a snowy hill.
 
Upvote 0

SelfSim

A non "-ist"
Jun 23, 2014
6,174
1,965
✟176,444.00
Faith
Humanist
Marital Status
Private
.. I rather think that your example is confusing the large surface area of tread and tire that allows him to ride on the surface as in the video I saw last night.
Yeah but this dude's heavy foot always spins his 4 wheels as the intial condition! Surely the main aim in towing a stuck vehicle is to make use of static friction between his own tires and the sandy/muddy surface(?) I think his initial thinking is to get buoyant, as if that makes his situation any better(?)

Ponderous Curmudgeon said:
On another note, deflating the tires on your own vehicle will increase traction and is commonly done in sandy conditions, it increases the contact area with the sand. I can't see it would help with the towed vehicle.
I think this particular dude is obsessed with buoyancy(?) His strategy is to rebuild his vehicles so they're as light as possible .. I guess so as to not end up getting stuck himself .. (which he usually ends up doing anyway).
Just goes to show how the idea one starts out with in one's head, (whatever that might be - buoancy in his case), sets in train what will happen, eh?

Ponderous Curmudgeon said:
And finally yes, the big V8 helps in that he can use his tires to dig through the surface till he finds purchase and then by applying multiple bursts of increased traction can pull the tiny car out of the mud. On the other hand, any normal tow truck driver will set his vehicle so that it won't slide and use the little electric winch on the back to do the actual work without wasting hundreds of dollars in tires. Real tow truck drivers use physics.
.. and also use some 'purchase power', by doubling or tripling the tow rope using pulleys? This dude obviously has a lot of weight to start out with (ie: the big V8). He carries and occasionally uses his winches, but his preference is always brute force and heavy foot action - get 'em spinning first! :D o_O
The classic was when he got stuck in a big bowl full of very dry sand. He whined about how it didn't matter which direction he took, the end result was always that both vehicles still remained trapped in it. Why he didn't stay at the bowl lip and use winches/buried anchors on the tow/winch vehicle, never seemed to occur to him.
(Oh yeah .. he's a 'give it a good yank' strategist too .. y'know, floor it to build up energy in the fabric tow rope and use that to overcome static inertia).

Ponderous Curmudgeon said:
I live on a snowy hill.
Fresh snow ain't too bad for grip. Its the refrozen meltwater (black ice) underneath that causes the big problems, eh?
Beats me why the dude (or the unthinking rescuees) don't use chains in such conditions?
 
Upvote 0

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
Yeah but this dude's heavy foot always spins his 4 wheels as the intial condition! Surely the main aim in towing a stuck vehicle is to make use of static friction between his own tires and the sandy/muddy surface(?) I think his initial thinking is to get buoyant, as if that makes his situation any better(?)

I think this particular dude is obsessed with buoyancy(?) His strategy is to rebuild his vehicles so they're as light as possible .. I guess so as to not end up getting stuck himself .. (which he usually ends up doing anyway).
Just goes to show how the idea one starts out with in one's head, (whatever that might be - buoancy in his case), sets in train what will happen, eh?

.. and also use some 'purchase power', by doubling or tripling the tow rope using pulleys? This dude obviously has a lot of weight to start out with (ie: the big V8). He carries and occasionally uses his winches, but his preference is always brute force and heavy foot action - get 'em spinning first! :D o_O
The classic was when he got stuck in a big bowl full of very dry sand. He whined about how it didn't matter which direction he took, the end result was always that both vehicles still remained trapped in it. Why he didn't stay at the bowl lip and use winches/buried anchors on the tow/winch vehicle, never seemed to occur to him.
(Oh yeah .. he's a 'give it a good yank' strategist too .. y'know, floor it to build up energy in the fabric tow rope and use that to overcome static inertia).

Fresh snow ain't too bad for grip. Its the refrozen meltwater (black ice) underneath that causes the big problems, eh?
Beats me why the dude (or the unthinking rescuees) don't use chains in such conditions?
 
Upvote 0

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
Makes for fun videos, but no, he has no clue buoyancy is only taking away from his objective. As for fresh snow, when it hits an inch per hour, tractor trailers cannot climb the hill in front of my house even if the road surface is above freezing because they effectively hydroplane at any speed until the plows come by. It is sort of fun to watch in a schadenfreude sense.
 
  • Like
Reactions: SelfSim
Upvote 0
This site stays free and accessible to all because of donations from people like you.
Consider making a one-time or monthly donation. We appreciate your support!
- Dan Doughty and Team Christian Forums

Ponderous Curmudgeon

Well-Known Member
Feb 20, 2021
1,477
944
65
Newfield
✟38,862.00
Country
United States
Faith
Non-Denom
Marital Status
Divorced
Give me an update tomorrow, ha ha.
Fell off after about 20 hours. still very slightly damp but won't hang with more than 50% over the edge. about the same as dry.
 
  • Like
Reactions: Chesterton
Upvote 0

Ophiolite

Recalcitrant Procrastinating Ape
Nov 12, 2008
8,619
9,593
✟239,894.00
Country
United Kingdom
Faith
Agnostic
Marital Status
Private
Fell off after about 20 hours. still very slightly damp but won't hang with more than 50% over the edge. about the same as dry.
That's great. Hope you didn't hurt yourself, but what about the towel?
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,911
3,964
✟276,869.00
Faith
Christian
Marital Status
Single
Fell off after about 20 hours. still very slightly damp but won't hang with more than 50% over the edge. about the same as dry.
If I wasn't aware of this thread I would suspected this was some bizarre experiment involving nappies.
 
Upvote 0
This site stays free and accessible to all because of donations from people like you.
Consider making a one-time or monthly donation. We appreciate your support!
- Dan Doughty and Team Christian Forums

Chesterton

Whats So Funny bout Peace Love and Understanding
Site Supporter
May 24, 2008
23,815
20,224
Flatland
✟865,803.00
Faith
Eastern Orthodox
Marital Status
Single
Fell off after about 20 hours. still very slightly damp but won't hang with more than 50% over the edge. about the same as dry.
A true man of science you are. :)

Unless you're female. (Just want to cover myself there.)
 
Upvote 0