THE 8 TYPES OF FLUIDS AND THEIR CHARACTERISTICS - SCIENCE - 2025

Traditionally, four types of fluids are recognized, which are classified taking into account their properties and the changes that they can present under the same atmospheric conditions. These are ideal fluid, real fluid, Newtonian fluid, and non-Newtonian fluid.

Other scientists take into account other classification methods, according to which fluids can be categorized according to the speed of movement of the fluid, its ability to be compressed, its viscosity and its rotational movement.

To begin with, fluids are substances that do not have a defined shape, that can flow easily (hence their name) and that cannot resist any type of shear force, so they are continuously deformed.

Fluids can be found in different states of matter: liquids, gases, plasma and some plastic solids make up the group of fluids.

The term "fluids" is often used as a synonym for liquids. However, this excludes the presence of gases, plasmas and plastic solids as fluids, so it is not suitable.

Main types of fluids

Ideal fluids

Ideal fluids are those that cannot be compressed and also have no viscosity.

Its name comes from the fact that it is an idealized fluid, since all existing fluids have a certain level of viscosity.

Real fluids

Unlike ideal fluids, real fluids do have viscosity. Generally speaking, all fluids are real fluids.

For example: water, kerosene, gasoline, oil.

Newtonian fluids

Newtonian fluids are those that behave according to Newton's laws of viscosity.

This means that the viscosity of the fluid does not vary according to the force applied to it. In addition to this, the viscosity decreases as the temperature increases.

For example: water, air, emulsions.

Non-Newtonian fluids

Non-Newtonian fluids exhibit behavior that could be considered abnormal, since they do not follow Newton's laws.

In these fluids, the viscosity varies with force. There are even cases in which non-Newtonian fluids can behave as solids, if a constant force is applied.

For example: suspensions of cornstarch in water (magic mud).

In a cup of water, add two cups of cornstarch and stir. When the mixture is taken with the hands and a constant force is applied to it (kneading it with circular movements), the fluid goes from being a liquid to a solid.

This behavior is maintained only while force is being applied. If you stop kneading, the fluid becomes liquid again.

Other examples of non-Newtonian fluids are mud and cement. Other substances, such as blood, mucus, lava, mayonnaise, jam and chewy candies, have non-Newtonian fluids that give them the consistency they have.

Types of fluids according to velocity

According to the speed of movement of the fluids, these can be stable or unstable.

In stable fluids, velocity maintains its modulus, direction, and direction throughout the fluid path.

However, in unstable fluids, the speed can vary. For example, the water in a river does not flow steadily: at some points it collides with obstacles and recedes, swirls or changes direction.

Each of these movements involves changes in the vector of the river's movement.

Types of fluids according to their ability to be compressed

According to the ability to be compressed, the fluids can be compressible and non-compressible. Liquids are practically impossible to compress, while gases have a great capacity to compress.

An example of the low compression capacity of fluids is hydraulic systems.

On the other hand, an example of the high compression capacity that air has are balloons and tires.

For example, a balloon can be filled with more air than its limits can support because the molecules that make up air are compressed to make way for more air.

Types of fluids according to their viscosity

Viscosity is the level of resistance that a fluid presents to the action of shear forces. It is the measure of friction between the different layers that make up a fluid; said friction occurs to set all the layers in motion.

For example, let's consider a mix to make a cake. When we use a paddle to stir the dough, only the portion of the dough adjacent to the paddle is moved.

But if we keep the paddle moving, friction will occur between the layers of the fluid, causing them all to move.

The viscosity of a fluid varies with temperature. When the temperature of the fluid increases, the viscosity of the fluid decreases.

For example: consider maple syrup. When the syrup is in the bottle, it is sticky and viscous. However, when we put it on a hot waffle, it becomes more watery (loses viscosity).

There are two types of fluids according to their viscosity: viscous and non-viscous. In practice, all fluids have viscosity, however, the level is higher in some. For example: water is less viscous than cake mix.

Types of fluids according to rotary motion

According to the rotary motion, the fluids can be rotary or non-rotary.

To check what type of fluid it is, you can put a small object on the fluid and let it be moved by it.

If the object rotates on itself, then it is a rotating fluid. If the object follows a current, then the fluid is non-rotating.

For example, in a river, you can see how the water swirls around the obstacles. At those times, the movement of the water is rotary.

Now let's consider the water in a bathtub that is being drained. For example, a rubber duck will spin around the drain but not on itself.

This means that you are following a stream. Hence, away from the vortex, the motion is non-rotary.

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