Not Slippery When Wet

Chesterton

Whats So Funny bout Peace Love and Understanding
Supporter
May 24, 2008
23,749
20,197
Flatland
✟860,379.00
Faith
Eastern Orthodox
Marital Status
Single
I tossed a dishtowel at the edge of the kitchen sink hoping to drape it over the edge. It was a bad toss, but it got the job done. There was about 20% of the towel on one side of the edge and 80% on the other, but it didn't slide off, because it was damp. I was reminded how, if I drape a wet material over the shower curtain rod, there's a lot more "grip" or friction when I try to pull it along the rod. This seemed like it should be counter-intuitive, because water is famous for making things more slippery, not less. Car tires have less friction with roads, not more, when the road is wet.

I couldn't find much about this, except this page here:

Why is clothes-wet skin friction coefficient higher than clothes-dry skin?

where someone mentions that they also couldn't find much. His question is asking about skin, so he gets a couple of skin-related answers, but I think his question is just a subset of mine.

Does anyone here think the answers regarding surface tension and capillary action are correct? Could it also simply be that, for example, when you put a damp material on a curtain rod, the rod becomes damp and so the water molecules on both surfaces are attracting each other? Anyone have a different answer?
 
Last edited:
  • Like
Reactions: durangodawood

Chesterton

Whats So Funny bout Peace Love and Understanding
Supporter
May 24, 2008
23,749
20,197
Flatland
✟860,379.00
Faith
Eastern Orthodox
Marital Status
Single
I always thought it had to do with weight. The extra weight of the wet towel caused additional friction pressure in excess of any slippery effect caused by the water.
I thought of that but I don't think it would account for the approx. 80%/20% distribution of the dishtowel I mentioned. Weight probably figures into it, but if it had much to do with weight, gravity should have pulled the towel off the edge toward the 80% side.
 
Upvote 0

FrumiousBandersnatch

Well-Known Member
Mar 20, 2009
15,258
8,056
✟326,229.00
Faith
Atheist
I'd guess surface tension plays a role as well as weight - if the surface is wettable, the uneven surface of cloth means that there's lots of places where water connects from cloth to surface and lots of places in between where it doesn't. That means a lot of surface tension at the boundaries, holding the cloth to the surface. As I understand it, capillary action is a similar phenomenon.

You could test if this makes a significant difference by trying it on a relatively non-wettable (hydrophobic) surface. I would expect it to slide off more easily if I'm right.
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,854
3,889
✟273,845.00
Faith
Christian
Marital Status
Single
The issue can be explained in terms of viscosity which is the resistance of a fluid to shearing as illustrated.
shear.png
A fluid such as water can be modelled as being composed of layers where there is an internal friction between each layer.

In the case of driving a car (the moving layer) on a wet road (the stationary plate), the high RPMs of car tyres results in shear rates which easily overcomes the internal friction between the layers hence the slippery road conditions.

By comparison pulling wet material over your shower curtain rod results in a far lower shear rate and the grip you are feeling is the resistance of the water to shearing.
 
  • Winner
Reactions: Chesterton
Upvote 0

durangodawood

Dis Member
Aug 28, 2007
23,411
15,559
Colorado
✟428,017.00
Country
United States
Faith
Seeker
Marital Status
Single
The issue can be explained in terms of viscosity which is the resistance of a fluid to shearing as illustrated.
shear.png
A fluid such as water can be modelled as being composed of layers where there is an internal friction between each layer.

In the case of driving a car (the moving layer) on a wet road (the stationary plate), the high RPMs of car tyres results in shear rates which easily overcomes the internal friction between the layers hence the slippery road conditions.

By comparison pulling wet material over your shower curtain rod results in a far lower shear rate and the grip you are feeling is the resistance of the water to shearing.
But is there really an x distance in the damp towel case? It seems that we can't model this problem in terms of layers of water.
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,854
3,889
✟273,845.00
Faith
Christian
Marital Status
Single
But is there really an x distance in the damp towel case? It seems that we can't model this problem in terms of layers of water.
In the diagram x is exaggerated and can be a few microns thick.
In the case of the damp towel the other consideration is the surface energy the towel is resting on.
Berry_Global-600x313.png
For a high surface energy such as acrylic coated laminex benches found in kitchens the highly polar nature of water due to the electronegativity differences between the oxygen and hydrogen atoms allows water from the damp towel to wet out and adhere to the surface.

surface_wet.jpg
The damp towel is literally stuck to the surface.
 
Last edited:
Upvote 0

Chesterton

Whats So Funny bout Peace Love and Understanding
Supporter
May 24, 2008
23,749
20,197
Flatland
✟860,379.00
Faith
Eastern Orthodox
Marital Status
Single
The issue can be explained in terms of viscosity which is the resistance of a fluid to shearing as illustrated.
shear.png
A fluid such as water can be modelled as being composed of layers where there is an internal friction between each layer.

In the case of driving a car (the moving layer) on a wet road (the stationary plate), the high RPMs of car tyres results in shear rates which easily overcomes the internal friction between the layers hence the slippery road conditions.

By comparison pulling wet material over your shower curtain rod results in a far lower shear rate and the grip you are feeling is the resistance of the water to shearing.
Thanks. As far as I can tell, that's a great answer.
 
Upvote 0

Bob Crowley

Well-Known Member
Supporter
Dec 27, 2015
2,999
1,858
69
Logan City
✟747,316.00
Country
Australia
Faith
Catholic
Marital Status
Married
The issue can be explained in terms of viscosity which is the resistance of a fluid to shearing as illustrated.
shear.png
A fluid such as water can be modelled as being composed of layers where there is an internal friction between each layer.

In the case of driving a car (the moving layer) on a wet road (the stationary plate), the high RPMs of car tyres results in shear rates which easily overcomes the internal friction between the layers hence the slippery road conditions.

By comparison pulling wet material over your shower curtain rod results in a far lower shear rate and the grip you are feeling is the resistance of the water to shearing.

Is this an example of Van Der Waals forces in action, which basically boils down to electromagnetic force?

Apparently this is the same force which allows geckos to climb windows.

Geckos' Sticky Secret? They Hang by Toe Hairs | Live Science

I suppose I'm curious about how geckos unstick themselves since they could hardly control the thousands of tiny hairs individually to change the angle and therefore increase or decrease their stickability.
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,854
3,889
✟273,845.00
Faith
Christian
Marital Status
Single
Is this an example of Van Der Waals forces in action, which basically boils down to electromagnetic force?

In this particular example no; the properties of water such as surface tension and adhesion to surfaces is determined by dipole-dipole or hydrogen bonding.
Due to electronegativity differences between the oxygen and hydrogen atoms, water molecules form a dipole where there is negative charge concentration around the oxygen atoms and a positive charge around hydrogen atoms.
As a result there is an electrostatic force between the water molecules or dipoles as illustrated.

S04mDaX3SrK5mGpZRBEF_hbondnet.jpg

Van Der Waal or London dispersion forces involve instantaneous dipoles.
In the case there is no ‘permanent dipole’ as in the case of the water molecule.
An instantaneous dipole is formed when there is an uneven distribution of electrons within the molecule.
Electrons are mobile and their distribution varies with time.
At any instant there could be an excess of electrons forming a negative charge concentration while a deficit produces a positive charge distribution as illustrated.

image_Van.png

These instantaneous dipoles can form bonds with each other which is the Van Der Waal force.

Apparently this is the same force which allows geckos to climb windows.

Geckos' Sticky Secret? They Hang by Toe Hairs | Live Science

I suppose I'm curious about how geckos unstick themselves since they could hardly control the thousands of tiny hairs individually to change the angle and therefore increase or decrease their stickability.

Van Der Waal forces are extremely weak when compared to other forces as shown in the comparison bond energies.

Bond-Energy-Comparison.png

I suppose the Van der Waal force is strong enough to support a Gecko’s weight, but not strong enough to impede a Gecko’s movement.
 
Last edited:
  • Informative
Reactions: Astrophile
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

FrumiousBandersnatch

Well-Known Member
Mar 20, 2009
15,258
8,056
✟326,229.00
Faith
Atheist
I suppose I'm curious about how geckos unstick themselves since they could hardly control the thousands of tiny hairs individually to change the angle and therefore increase or decrease their stickability.
I think they 'peel' their feet off the surface (Post-It Note style). That way, they're breaking the bonds at the narrow moving boundary between stuck and unstuck.
 
  • Like
Reactions: public hermit
Upvote 0

Bob Crowley

Well-Known Member
Supporter
Dec 27, 2015
2,999
1,858
69
Logan City
✟747,316.00
Country
Australia
Faith
Catholic
Marital Status
Married
I suppose the Van der Waal force is strong enough to support a Gecko’s weight, but not strong enough to impede a Gecko’s movement.

I think they 'peel' their feet off the surface (Post-It Note style). That way, they're breaking the bonds at the narrow moving boundary between stuck and unstuck.

Thanks for the responses.
 
Upvote 0

Tanj

Redefined comfortable middle class
Mar 31, 2017
7,682
8,316
59
Australia
✟277,286.00
Country
Australia
Faith
Atheist
Marital Status
Married
Thanks. As far as I can tell, that's a great answer.

It isn't though. What you need to do is try this experiment with a towel made of car tyre rubber, then go for a drive on a wet road in a car with tires made out of towel.
 
Upvote 0

Chesterton

Whats So Funny bout Peace Love and Understanding
Supporter
May 24, 2008
23,749
20,197
Flatland
✟860,379.00
Faith
Eastern Orthodox
Marital Status
Single
It isn't though. What you need to do is try this experiment with a towel made of car tyre rubber, then go for a drive on a wet road in a car with tires made out of towel.
Well, after I thought about it, I was wondering why he says the slipperiness of tires is due to the RPM. If you were driving on a wet road and slammed on the brakes, the tires wouldn't be revolving but I think they'd still be more slippery than if you did that on a dry road.
 
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

sjastro

Newbie
May 14, 2014
4,854
3,889
✟273,845.00
Faith
Christian
Marital Status
Single
Well, after I thought about it, I was wondering why he says the slipperiness of tires is due to the RPM. If you were driving on a wet road and slammed on the brakes, the tires wouldn't be revolving but I think they'd still be more slippery than if you did that on a dry road.
I thought it would be rather self evident.
On a wet road you are more likely to skid braking suddenly from a speed of 100 kph than 20 kph which depends on the RPMs.
The higher the wheel RPMs the greater the shear rates on the water which reduces its internal friction or viscosity.
When you brake, the car is still moving due to inertia and the shear rate depends on the velocity of the car even though the wheel RPMs have dropped to zero.
 
Upvote 0

Ophiolite

Recalcitrant Procrastinating Ape
Nov 12, 2008
8,521
9,493
✟236,458.00
Country
United Kingdom
Faith
Agnostic
Marital Status
Private
The higher the wheel RPMs the greater the shear rates on the water which reduces its internal friction or viscosity.
That doesn't read correctly. Water is, as near as makes no difference, a Newtonian fluid and so it has a fixed viscosity. If it were non-Newtonian then an increased shear rate would reduce the apparent viscosity. Are you arguing water is not, essentially, Newtonian?
 
Upvote 0

sjastro

Newbie
May 14, 2014
4,854
3,889
✟273,845.00
Faith
Christian
Marital Status
Single
That doesn't read correctly. Water is, as near as makes no difference, a Newtonian fluid and so it has a fixed viscosity. If it were non-Newtonian then an increased shear rate would reduce the apparent viscosity. Are you arguing water is not, essentially, Newtonian?
Yes you are correct I used sloppy terminology.
If water was a non Newtonian fluid then the internal friction could be equated with viscosity.
In the layer model for water the internal friction between the layers is due to hydrogen bonding not viscosity.
The issue remains the same whether the shear forces are enough to overcome the internal friction between the layers.
 
Upvote 0

Chesterton

Whats So Funny bout Peace Love and Understanding
Supporter
May 24, 2008
23,749
20,197
Flatland
✟860,379.00
Faith
Eastern Orthodox
Marital Status
Single
I thought it would be rather self evident.
On a wet road you are more likely to skid braking suddenly from a speed of 100 kph than 20 kph which depends on the RPMs.
The higher the wheel RPMs the greater the shear rates on the water which reduces its internal friction or viscosity.
When you brake, the car is still moving due to inertia and the shear rate depends on the velocity of the car even though the wheel RPMs have dropped to zero.
Yes, but that doesn't address what I said.
 
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

sjastro

Newbie
May 14, 2014
4,854
3,889
✟273,845.00
Faith
Christian
Marital Status
Single
Yes, but that doesn't address what I said.
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.
 
Upvote 0