What is a non-Newtonian fluid?

A non-Newtonian fluid is one that does not have a defined and constant viscosityunlike conventional fluids that follow Newtonian mechanics.

In Newtonian fluids, viscosity can be described as a function of temperature and pressure with no other forces involved. In non-Newtonian fluids, on the contrary, the viscosity depends on the temperature and shear force to which the fluid is subjected.

Water is one of the best examples of a Newtonian fluid; As non-Newtonian fluids we can mention honey, blood, numerous types of gels and paints, etc.

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A non-Newtonian fluid at rest behaves like a liquid while if it is subjected to stress forces, its viscosity increases. If you hit the surface of a non-Newtonian fluid, the stress introduced by the incoming force causes the atoms that make up the fluid to rearrange, increasing the viscosity, even up to behave like a solid for an instant. Your hand will not penetrate the fluid.

But if you go slowly inserting your hand into the fluid, however, you will be able to get it into the fluid without problems. And if the hand is inside and you try to get it out quickly, the fluid will behave like a solid again and you will be able to get the fluid out of the container next to your hand. The greater the applied force, the greater the viscosity. This effect usually lasts only as long as the force is applied.

Among the non-Newtonian fluids we can find the following large groups:

  • plastics
  • Fluids that follow the power law
  • viscoelastic fluids
  • Fluids whose viscosity is also affected by time


One of the most used non-Newtonian fluids as an example, being cheap and non-toxic, is the fluid formed by the suspension of corn flour in water. In the following video you can see this example.

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