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Understanding the importance of viscosity can be analyzed through two concepts: shear stress and shear rate.
During our earlier discussions we have talked about the contributions of Pascal, Bernoulli and Reynolds. Because of their work we now have a pretty good understanding of hydraulics and lubrication theory. Their work spanned about 250 years from 1653 to 1900. Now, we'll look at how some additional scientific greats have helped with our understanding of viscosity.
Most of us involved in the general lubrication industry know that viscosity, the resistance to flow of a fluid, is a pretty important property of lubricants-in fact probably the most important.
Why is it important to understand viscosity? Because viscosity is central to the performance of lubricated machinery, such as your car:
* If you use high-viscosity engine oil in your car, the oil puddles in your drive-way will be smaller, but your engine will run hotter and it probably won't start on a cold winter morning.
* If you use low-viscosity engine oil in your car, the piston rings may wear out in a few thousand miles, the crankshaft bearings may seize and the puddles in your driveway will amaze your neighbors.
As we said, the simplest definition of viscosity is resistance to flow. Sir Isaac Newton defined it as "the resistance that arises from lack of slipperiness in a fluid." Cold maple syrup is thick and not slippery, but cold water is thin and slippery.
Words such as thick, slippery, thin and sticky are...