Some visible viscoelastic manifestations

Clearly they are important in many practical and industrial applications. AU these effects arise essentially because of tension along the steamlines generated in the flow of these viscoelastic liquids which are not present in Newtonian liquids, and this tension is associated with the so-called rst normal-stress difference. 

In the case of a viscoelastic liquid the squeezing action arises from the tension along the circular streamlines which result in an inward strangulation force, otherwise called a hoop stress [2], 

Another (but smaller) non-hnear viscoelastic force called the second normal-stress difference (see later for an explanation of this term) has a special role to play in a number of other situations such as 

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A Handbook of Elementary Rheology 14.2 Some visible viscoelastic manifestations... 

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