Wet Friction: Exhaustive Insights, Examples, Problems, and FAQs

In this article, we will see about one of the types of frictional force that acts on wet floors, known as wet friction.

Wet friction can be defined as the fundamental force of friction that can be seen between two surfaces of different nature (solid and liquid). It is mainly introduced to lower the intensity of friction acting between the surfaces. It exhibits less friction compared to dry friction.

Now let’s know about wet friction in detail, which is the post’s primary focus.

What is wet friction

Wet friction is almost kind similar to fluid friction but differs in some criteria.

The wet friction occurs between a rigid solid surface and loosely bound molecules of a liquid surface. It is one of the types of friction force that exhibits a lower value of friction that is determined with the help of a coefficient. We can get an idea by reading out its name.

Let us know in detail about materials that exhibit less friction.

Wet friction materials

Wet friction materials are those which, when in use, must cause low friction.

The materials that cause friction act in the fluid medium are known as wet friction. The natural material that possesses wet friction are fibers, resins, fillers, rubbers, oil, cork, paper, etc. If there is a need for continuous sliding appliances, wet friction materials are indeed beneficial.

Now let us know the coefficients of these wet friction materials.

Wet friction coefficient

The wet friction coefficient is a formula used to measure the value frictional force acting between solid and liquid surfaces.

In detail, we can say that to measure the coefficient of wet friction of certain materials, and we must first calculate the force of friction acting on individual surfaces. Then, we have to consider its ratio. It tells us the value of the opposing force needed to stop the body.

It is time to know which material exhibits more opposing force with the help of the coefficients list.

List of coefficient of wet friction in materials

Here are the coefficients of wet friction of some essential materials.

  Surface 1  Surface 2  Coefficient of wet friction
  Dry ice  Wet ice  0.19
  Brass  Ice  0.15
  Wax  Snow  0.04
  Zinc  Lubricant  0.04
  Tungsten  Liquid steel  0.1 – 0.2
  Leather  Metal  0.2

Now let us see some natural examples of wet friction.                                                      

Wet friction examples

The examples of wet friction that are mentioned below are some natural experiences that we observe daily.

Swimming in the pool

A swimmer must maintain his body balance in a streamlined position to exert some force to swim forward. Here the pool water exerts some amount of force on his body to stop him. Here the wet friction acts along with the layer of his skin and surface of moisture which is significantly less. Due to this, he will be able to swim.

kid 1401157 1280
Image Credit: Pixabay free images

Coral reefs

It is known that the coral reefs present will have a slight movement which is usually due to wet friction or fluid friction. This friction will be less or high depending on the number of irregularities on the two surfaces in contact.

Movement of Honey

We know that the flow of honey will be slow due to its thick density. Here the surface of the liquid layer, i.e., honey, and on the surface on which it is spread is solid exhibits wet force of friction on each other. Since the density is thick, it requires a high wet friction force to stop the movement of honey.

Wet friction
Image Credit: Pixabay free images

Movement of fishes in the ocean

Similarly, as a swimmer’s body is streamlined, even the fishes have the same body structure, which helps them move freely in the ocean water. The wet friction force acts between the layer of fish skin and the water’s surface (Solid and liquid surface); the friction will be lesser than making the movement manageable.

Wet friction
Image Credit:
Pixabay free images

Sucking cold beverage through a straw

When you drink a cold beverage with the help of a straw, you feel some difficulty to suck if the beverage is a little denser (thicker); if the liquid is thinner or less dense, you feel easy to suck it. Here wet friction plays a vital role in providing the right amount of force according to density.

Wet friction
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Splashing water onto your face during a play

When you visit a water place, you usually start to play by splashing water on your peer group, the density of water splashed depends entirely on the force of wet friction. If the wet friction is less, there will be a minor splash, and if the wet friction is high, the splash will be increased.

Wet friction
Image Credit:
Pixabay free images

Shaving cream

When you apply the shaving cream, it acts as a lubricant that reduces the wet force of friction between the blade’s surface and the face. Initially, there will be dry friction, but after applying cream, there will be wet friction that helps remove the unwanted beard through easy movement.

Pressing toothpaste out of its tube

We find two types of toothpaste: some will be thicker in density, and the other will be thinner. We require more force to suck out the thicker toothpaste from its tube than the more delicate paste. Similarly, wet friction will be less in thinner toothpaste that making the movement manageable.

Wet friction
Image Credit:
Pixabay free images

After all these concepts, now let’s know about dry friction vs wet friction.

Dry friction Vs wet friction 

The essential differences between dry friction and wet friction are mentioned below,

Dry friction is the force of friction between two solid surfaces in contact.Wet friction is the force of friction between a solid surface and a liquid surface.
Vector QuantityVector Quantity
High frictionLow friction
Ex:   MatchstickEx:   Oil on window hinges.

After these differences, let us look at the critical effects of wet friction as mentioned next.

Stirbeck curve

Stirbeck curve is one of the main ideas that help in the demonstration of wet friction.

The Stirbeck curve is used in higher machines to know the efficiency and is mainly used in the concepts of tribology. It shows the relationship between objects which are lubricated with fluids, when plotted, shows a non-linear curve of the contact surface-viscosity of the lubricant and its speed.

Now let us see some main factors that affect friction.

Factors affecting wet friction

The necessary factors that affect wet friction are given below,

  • The viscosity of the material.
  • Temperature and the area of a surface is one of the main factors.
  • Shape and nature of the material.
  • Speed of the flow or movement of object under consideration.
  • Pressure is the essential factor to be considered.

Now let us look into the ways of obtaining wet friction.

Ways of obtaining wet friction

There are numerous ways of obtaining wet friction. Some of them are mentioned below;

  • To make the floor smoother, we have to polish it.
  • To increase the coefficient of wet friction, you can make it smoother with the help of available lubricants.
  • Another way is to modify the objects in a streamlined shape to make it easier for them to get along with fluid friction.
  • Try to reduce the normal force when two surfaces are in contact with the help of thin liquids.
  • You can also obtain wet friction y reducing the area of contact between two surfaces.

It is time to know the problems with wet friction.

Problems based on wet friction

The following are some of the problems on wet friction to understand the overview of the concept.

Problem 1

Calculate the wet friction coefficient if F is given as 8N, the area is given as 10m, and the velocity gradient as 0.1/s?

Solution: One of the formulas to calculate the coefficient of wet friction is used below to solve the problem,

CodeCogsEqn 16 2

Substitute the values in the above formula,

8 = CodeCogsEqn 17 1 * 10 * 0.1

CodeCogsEqn 17 1 = 8 / 10 * 0.1

CodeCogsEqn 17 1 = 8

Therefore, the result of the coefficient of wet friction is 8

Problem 2

Find the value of wet friction coefficient if they have given the total wet frictional force as 20N and the normal force acting perpendicular on it is 28N?

Solution: The formula to calculate the coefficient of wet friction is given as follows,

F = CodeCogsEqn 18 2 N

Substitute the values in the above formula,

28 = CodeCogsEqn 18 2 * 20

CodeCogsEqn 18 2 = 28/20

CodeCogsEqn 18 2 = 1.4

Therefore, the value of the coefficient of wet friction is obtained be 1.4

Problem 3

A kid spills the water on the ground, here find the value of wet friction coefficient if they have given the total wet frictional force as 16N and the force acting perpendicular on the basis as 23N?

Solution: The formula to calculate the coefficient of wet friction is as follows,

F = CodeCogsEqn 18 2 N

Substitute the values in the above formula,

23 = CodeCogsEqn 18 2 * 16

CodeCogsEqn 18 2 = 23/16

CodeCogsEqn 18 2 = 1.43

Therefore, the value of the coefficient of wet friction is obtained be 1.43

Problem 4

Calculate the wet friction coefficient when a lubricant is added between the sideways of a door and given that F is 20N and the area of grease/ lubricant applied is given as 29m. The velocity gradient is given as 0.8/s?

Solution: The formula to calculate the coefficient of wet friction is used below to solve the given problem,

CodeCogsEqn 16 3

Substitute the values in the above formula,

20 = CodeCogsEqn 17 1 * 29 * 0.8

CodeCogsEqn 17 1 = 20 / 29 * 0.8

CodeCogsEqn 17 1 = 0.551

Therefore, the result of the coefficient of wet friction is 0.551

It is time to conclude by knowing some essential FAQs based on wet friction.

Frequently Asked Questions on Wet Friction | FAQs

Why do we feel difficult to move on a wet marble?

We feel challenged to move on a marble surface made up of marble due to its nature.

We know that for friction to occur, there is a need to have irregularities on the surface. Water spills on the marble surface cover all the microscopic gaps that lead to low friction. Therefore, making it difficult for the movement.

Can we eliminate friction?

We cannot wholly eliminate friction.

Any two surface in contact consistently exhibits some friction, whether it may be of significantly less value but cannot wholly eliminate it due to the presence of small pourings present on the surface that cause friction with substantially less effect.

Can friction oppose the direction of water in a container?

We cannot give any value of the wet friction coefficient to water.

For water, no criteria or factors of wet friction can be applied. But it can act as a lubricant that can help in reducing friction on a surface. Therefore, as it acts as a lubricant, the direction of water cannot be changed by a container.

Why is there less friction on wet surfaces?

Liquid or fluid matter has lesser irregularities.

When you spread the liquid on the surface, it covers all the irregularities supposed to produce opposing force for the surface in contact. Due to this, there will be low shear of liquid that reduces the amount of friction compared to the previous dry friction and makes the surface slippery.

Which one among dry and wet surfaces creates more friction?

Sometimes water may be the sole cause for an increase or decrease in friction.

Usually, dry friction causes more force of friction. Whereas in wet friction, the liquid decreases the friction between tires and the ground. But in some cases, we can observe that water present between fingers and paper causes high friction. So any friction can cause an increase in the force of friction.

Which friction is preferred more?

Wet frictional is more effective in showing the working of an object.

In general, we all prefer wet friction; wet is preferred more due to the tendency to remove frictional heat with the help of water or air.

Is there the presence of friction on a wet surface?

Of course, there will be a minimum amount of friction present on all the surfaces.

Let’s consider an example of our human skin. When we apply a lotion on our hands, the skin becomes automatically smooth, causing the wet friction coefficient to be activated, and in some cases, it is slightly high compared to dry friction.

Which constitutes more friction, dry or wet?

Dry surfaces have more amount of friction in comparison to wet surfaces.

On a dry surface, there will be more coefficient of friction as there will be a high tendency to produce opposing force. On wet surfaces, the wet friction will become significantly less in terms of coefficient of friction, and the opposite force is less.

Does rain reduce the force of friction?

Rain can bring change in the effect of friction.

We know that water spread in a certain amount acts as a lubricant. Before heavy rain, there will be only two surfaces, i.e., the surface of the vehicle tire and a dry surface of the street. But after rainfall, a new layer is introduced between the dry surfaces that lead to the drop in friction.

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