When Water acts like Glue (flat surfaces)

[Sergio Silva]

Water like glue

This topic could have more meaning on a chemistry forum.

Firts of telling my doupt, i will inform you why i put this question. My goal is controlling an obejct more accurately.

I notice that sometimes a solid with plain face on a wet surface is difficult to remove. Besides it tends to follow the liquid (i'm not sure about this part).

I am suprising by the force that is needed. In this moment i need some basic explanations about the chemistry or the physics of this event.

If what i wrote above is right could this be a creasy way of transportation.

Thanks

 

[Baluncore]

Close flat surfaces, of hydrophilic materials, hold water in the gap by capillary action. The surfaces are held together by the attraction of the fluid water molecules to the surface materials.

If the surfaces are very flat, and they are wrung together, which pushes out almost all the water, the surfaces will be held together by atmospheric pressure. The surfaces cannot be separated unless air can enter between the surfaces, but one surface may still slide on the other.

 

[Bystander]

https://www.google.com/search?q=gau...I4OTcyajBqN6gCALACAA&sourceid=chrome&ie=UTF-8

 

[Sergio Silva]

Close flat surfaces, of hydrophilic materials, hold water in the gap by capillary action. The surfaces are held together by the attraction of the fluid water molecules to the surface materials.

If the surfaces are very flat, and they are wrung together, which pushes out almost all the water, the surfaces will be held together by atmospheric pressure. The surfaces cannot be separated unless air can enter between the surfaces, but one surface may still slide on the

I am confused.They are glued by atmospheric molecules or water molecules? And if it slides, it slides for the same type of molecules?. With carefully push of the solid object it will follow the theorytical wet trail?

 

[Sergio Silva]

The two surfaces are glued by atmospheric air and some by water molecules. Some questions arise (I think). Water vapor is considered atmospheric air? What is the role of water molecules? Could we talk on atmons instead?
I red the article about 3 types of wringing. 1-air pressure; 2-pressure from oil (or water from oil); 3-By small distance (mm ??). What i want to know is why and how this hapen on atom size to pursuit my goal. One more think, they could slide, dont they?

 

[Baluncore]

I am confused. They are glued by atmospheric molecules or water molecules?

The surfaces are attracted by the water molecules.

Surfaces, held together by a film of water, can slide against each other. The liquid water is sheared as the surfaces slide.

When you separate two surfaces, the gap between them must be filled with air, or external atmospheric pressure will hold them together.
Viscous air must enter through the very narrow gap between the surfaces, before they can come apart. If that gap contains some viscous liquid water, then the air may not be able to quickly enter.

 

[DaveC426913]

It is essentially the same outcome as a suction cup.

A suction cup is held to a surface by atmospheric pressure. If no air can get under the cup into the partial vacuum, then it will be difficult* to lift it.

Essentially on a wet surface, the film of water stands in to make the air-tight seal.* not impossible. It's only held by atmospheric pressure, which maxes out at 14.7psi. So an object with a 1 square inch contact area will hold (ideally, but not actually) with 14.7 pounds of pressure against you trying to lift it off.

 

[DaveC426913]

If the surfaces are very flat, and they are wrung together, which pushes out almost all the water...

TIL a broader application of the word wrung/wring. I have never heard it applied to anything other than what one does to a towel (or hands).

I mean, I guess it's the same application. The definition is: : to squeeze or twist especially so as to make dry or to extract moisture or liquid.

 

[Baluncore]

There are a couple of macro examples of this combined effect, where water helps seal the air gap.

One is splitting or breaking solid rocks with "feathers and wedges". You must not hurry, insert the wedges and then give it time for air to enter the gap as a crack forms in the rock. When you return later, the crack will, hopefully, have opened sufficiently to proceed with separation. If the rock is wet, the movement of air into the capillary gap will be blocked by the more viscous water, and it will take more patience to split the rock. It is easier to break dry or porous rock than solid rock, and not for only the obvious reason. Water-jet cutting and laser cutting both fill the cut under pressure, as the kerf is created, so do not have the same speed restriction as opening a crack.

Trees stand with a root system that branches and spreads out, to hold the soil together. The roots penetrate to the wet clay of the sub-soil. That root system takes the form of a huge sucker, that holds each tree to the face of the planet, by both gravity and by atmospheric pressure. A strong steady wind, or a gust, can induce sideways forces on trees that are significantly greater than gravity can normally counter against a fulcrum. That explains why trees and forests, that survived greater winds during normal soil moisture conditions, can fall in lower winds during droughts. Loss of water from the soil allows air to enter deep into the soil, below the roots, which breaks the suction, allowing the tree to be overturned.
A sucker with a 20 ft diameter, (120" radius), holds down with a force of;
3.14159 * 120" * 120" * 14.7 psi = 665 thousand pounds.
That is 301,639 kg = 300 tonne. When generating flat surfaces using the "Whitworth three plate method", the surfaces must remain wet or contaminated with a fine dust. If the polished surfaces are clean and dry when they are wrung together, they will instantly cold-weld, forming molecular bonds between the two flat surfaces as air is excluded. Separation along the previous joint surface will be very difficult and will spoil the finish.

 

[Mister T]

I am confused.They are glued by atmospheric molecules

The atmospheric molecules are attracted, by gravity, to the Earth. It is this attraction that is responsible for atmospheric pressure. It is also the force pushing down on the object that makes it seem like the object is "glued" to the surface.

 

[Nugatory]

A suction cup is held to a surface by atmospheric pressure. If no air can get under the cup into the partial vacuum, then it will be difficult* to lift it.
......
* not impossible. It's only held by atmospheric pressure, which maxes out at 14.7psi. So an object with a 1 square inch contact area will hold (ideally, but not actually) with 14.7 pounds of pressure against you trying to lift it off.

Although for a good time, we could try pulling a suction cup off of a piece of smooth ceramic underneath a few meters of water....

 

[Sergio Silva]

The atmospheric molecules are attracted, by gravity, to the Earth. It is this attraction that is responsible for atmospheric pressure. It is also the force pushing down on the object that makes it seem like the object is "glued" to the surface.

Like f1 cars skirts to produce ground force effect (or vacuum). My problem is that i use water and i want to know if the solid follows the water path. I remember staying at coffee and a servant put an aluminium tray on the table who was wet. The aluminium tray could slide on surface but to remove it from table needed a lot of effort. I am not saying if i pull the trail not fall out at the floor, but if it would have tedencie to follow the water splash.Am i right?

 

[Sergio Silva]

Reading your phorum give me some thoughts. If water seals the air, when the water trail ends the effect disapear. In other hand i think that the atoms of water have a tendency to being attracted to close flat surfaces. I need a explain about that. And if the tray is more heavy the effect is equal, it isint?

 

[Baluncore]

In other hand i think that the atoms of water have a tendency to being attracted to close flat surfaces. I need a explain about that.

https://en.wikipedia.org/wiki/Capillary_action#Capillary_rise_of_liquid_in_a_capillary

 

[Sergio Silva]

https://en.wikipedia.org/wiki/Capillary_action#Capillary_rise_of_liquid_in_a_capillary

Well, i think that you gave me the facts. Water height vs capillary effect. But you dont gave a explanation about why this occurs. Why water have the ability to glue to everything that is on some range. Its the same with teapods, some spills other not. The ones that spill, albeit gravity, glue with surface (or walls) of teapods. I red something about the air. When a plane is flying the air passing sticks to its surface. Other examples exist, shark skin and others.

 

[Sergio Silva]

Well, i think that you gave me the facts. Water height vs capillary effect. But you dont gave a explanation about why this occurs. Why water have the ability to glue to everything that is on some range. Its the same with teapods, some spills other not. The ones that spill, albeit gravity, glue with surface (or walls) of teapods. I red something about the air. When a plane is flying the air passing sticks to its surface. Other examples exist, shark skin and others.

A error, skin shark repels water

 

[Baluncore]

https://en.wikipedia.org/wiki/Hydrophile

 

[Sergio Silva]

Further research indicate coanda effect to explain the case of teapod. If it was with water the result would be the same. In conclusion i think i am being putting questions that are not essencial to this topic. But i have the problem of weight of the sheet of metal. If the weight increases we need more water to seal the vaccum or am i making a huge confusion.

 

[Baluncore]

If the weight increases we need more water to seal the vaccum or am i making a huge confusion.

You probably want a simple theory of everything that is wet. Unfortunately, that is not possible. There are many small effects, that together, give us the universe we experience.
Water is a polar molecule, that exhibits surface tension.
https://en.wikipedia.org/wiki/Properties_of_water#Polarity_and_hydrogen_bonding