The limit of Newtonian behaviour

Note the onset of non-Newtonian behaviour at a shear stress of around 2000 Pa. 

It has even been estimated that pentane becomes non-Newtonian above shear rates of 5 x 10 s-i, while water would have to be sheared at an impossible s l in order to see any non-Newtonian behaviour  

Exercise Ask a number of untrained people to estimate how much thicker the 

In this chapter we will look at a number of situations where, if we know the (Newtonian) viscosity of a liquid, we are able to predict something about its flow in certain simple geometries. First we will look at flows where the viscosity alone is important, and then we will see what happens when we have to take the hquid s density into accoimt, so that secondary flows and eventually turbulence are seen in high-speed flows. Lastly, we will consider some flow situations where surface tension as well as viscosity is important. Learning to use these equations is a very useful precursor to looking at non-Newtonian equations. They can also be used to obtain an order of magnitude estimate of many comphcated flow situations. 

Important One of the greatest difficulties for beginners is to realise that consistent units must be inserted into equations, and here we adhere to the SI system, see Qiapter 2, where all parameters are reduced to a seconds, meters and kilograms basis.  

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