Normally, an increase in pressure causes a fluid’s viscosity to increase, too. Three factors determine a substance’s flow behavior. Still, shear rate is not the only influencer. To learn more consult “ The Rheology Handbook”. The flow behavior of non-Newtonian liquids can be far more complex than these basic examples. yogurt), while for others the viscosity increases with increasing shear rate (curve 3 | e.g. If its viscosity changes with the shear rate, a liquid is non-Newtonian and – for exact definition – one has to specify the apparent viscosity.ĭifferent shear-dependent fluids behave differently: For some, their viscosity decreases when the shear rate increases (curve 2 | e.g. Typical Newtonian liquids are water or salad oil. For a Newtonian liquid, this function is a straight line (curve 1) see figure 6. Such fluids are named ‘Newtonian liquids’ after Sir Isaac Newton.Ī viscosity function shows the viscosity over the shear rate. the shear rate – acting upon the fluid, it is ideally viscous. If a fluid’s internal flow resistance is independent of the external force – i.e.

High-viscosity fluids resist deformation. Fluids which flow easily show a low resistance to deformation. viscous fluids that contain an elastic portion. The specific field of viscometry covers ideally viscous fluids, and – considering certain restrictions – also viscoelastic liquids, i.e. sweet jelly) or as a viscoelastic liquid (like e.g. According to a material’s properties, we either classify it as a viscoelastic solid (like e.g. That is, substances which are neither completely elastic, nor entirely viscous. In everyday life, we mostly come across viscoelastic materials. Scientists specify solid materials as being elastic and liquids as being viscous. Imagine all materials as classified on a virtual scale from solid to liquid. Rheology deals with the flow behavior and deformation of materials.

In order to determine a fluid’s viscosity, you have to enter the field of viscometry, a subject area of a wider science called rheology.

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