Why does the specific viscosity have no unit


What is it actually viscosity and how does it explain the different flow behavior of water and oil? You can find out here.

Definitely still watch that Videoto the article. All important information is audiovisually prepared for you in it.

Viscosity explained simply

The viscosity or toughnessgives you information about how thick a liquid is. Imagine pouring out a glass of oil and a glass of water. The oil flows slowly and slowly out of the glass and only piles up before it disperses. The water, on the other hand, flows quickly out of the glass and splashes in all directions when it hits the bottom.

That's because of the Viscosity of the fluid. That of oil is greater than that of water. This is why oil is so much thicker and more viscous and water so thin and flowable. So you say oil has a bigger one viscosity than water.

You differentiate between the so-called dynamic viscosity and kinematic viscosity .The dynamic viscosity depends on the temperature and the substance under consideration (water, oil, etc ...). The kinematic viscosity is the same dynamic viscosity divided by the density of the substance. The reference with the density enables you to compare different fabrics directly with each other. The kinematic viscosity and the dynamic viscosity are about density linked together.

The viscosity describes the viscosity of a liquid. The lower the viscosity, the thinner the fluid is. The greater the viscosity of a fluid, the thicker it is.

Kinematic and dynamic viscosity

Are you talking about viscosity, it is usually that dynamic viscosity meant. She is your measure of that toughness a liquid. As already said, the flowability of a liquid decreases with the size of it toughness. So the liquid is thicker. The unity of dynamic viscosity is the Pascal second ().

The kinematic viscosity is the dynamic viscosity divided by the density the liquid.

Its unit is square meters per second ().

To dynamic and kinematic viscosity we already have an article with Video prepared for you. Make sure to have a look there so that you get the full overview.

Viscosity liquids

The viscosity arises from the behavior of the Particle in the liquid. Particle viscous liquids, i.e. liquids with higher toughness, are more closely bound together and therefore less flexible. This is the so-called internal friction. These internal friction is not only created by the molecular forces, but also through the Impulse exchange between Particle

The effect of internal friction is best imagined by the movement of two interlocking layers of molecules lying on top of each other. They slide when flowing Molecules past each other. To overcome the interlocking, you need a certain amount of force. How big this force must be depends on your fluid.

You may have seen this in action in a lake. When a strong wind blows over the surface, the top layer is most excited. The deeper you go, the less you see the effect. After a few meters you don't feel any current at all. The force therefore decreases after each layer, which means that each layer has a different speed.

Depending on whether the resulting Speed ​​gradient behaves linearly or non-linearly, your liquid is one newtonian or non-Newtonian liquid

Newtonian fluids

At a Newtonian fluid the speed between the molecular layers decreases linearly. You describe fluids like water and air in terms of stress-independent toughness.

Opposite are the so-called non-Newtonian fluids.

Non-Newtonian fluids

At a non-Newtonian fluid if the speed does not propagate linearly. The viscosity so does not remain constant.

An example of this is mixing corn starch with water. From this you build one suspension. you now act on them with quick movements suspension a behaves like a Solid and not like a liquid.
So if you hit it with your fist, it will be absorbed suspension the full blow and no splashes fly through the air.


The viscosity you measure a liquid with a Viscometer. With this device, you put your sample into a gap between two bodies. One part of the assembly rotates while the other is at rest. Now you measure that Torquewhich you have to muster to keep the movement going. From this you get the Shear stress and with her the toughness.

Viscosity gases

Gases have one too viscosity. In contrast to liquids, however, this is mostly only dependent on the temperature and not on the pressure. The pressure only plays a role again when the gas is particularly dense or particularly thin.
Basically it is toughness of gases but only dependent on the temperature. In terms of temperature dependence, gases behave in the opposite way to liquids. As the temperature of the gases rises, so does the viscosity.

Viscosity example values

In the following table you can see some typical values ​​for the Viscosities different substances. Remember, the larger the value, the more viscous the fluid.