RESEARCH PROJECT : IS IT POSSIBLE TO WALK ON WATER ?

Newtonian fluids 

 

    What is a newtonian fluid ?

 

We talk about a Newtonian fluid when the viscosity of this fluid is independent

of the pressure which is applied to it. For example: water is a newtonian fluid, it’s not more viscous at rest or when we mix it slowly or quickly. A perfect newtonian fluid doesn’t exist, so we consider that water and air are newtonian fluids undergoing the same conditions, (example : water becomes a non-newtonian fluid under extreme pressure).

The viscosity of non-newtonian fluids changes when we apply on it a mechanical

stress but there are many groups of those fluids.

 

    Differents types of non-newtonian fluids :

 

We can distinguish four types of non-newtonian behaviour:

• Shear thinning : when you shake them or you press them, they become more liquid, so less viscous, they flow away more easily. In this group, there are specific cases like blood, lava, polish and toothpaste. They are pasty but they become liquid when the flow is quick.

• Shear thickening : Not as shear thinning, they become more viscous when we shake them, and are harder to mix. To a certain concentration, it can be a jelly. Those fluids like wet sand are harder when we push them quickly. For example, when you take wet sand with your hand and you open it, the sand is liquid. On the contrary, when you close your hand and you put a pressure on the sand, it becomes very hard (we can see the same things with corn flour mixed with water).

• Thixotropic fluids : they are like yoghurt, when you mix it, yogurt becomes more and more liquid. Yoghurt is called thixotropic.

• Anti-thixotropic fluids : if a fluid becomes on the contrary thicker and thicker when we mix it, it is called anti thixotropic like liquid cream which becomes whipped cream after a while.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

http://www1.lsbu.ac.uk/water/rheology.html