This viscosity measurement was given the term kinematic. Again, centistokes (cSt) is used for easier readings.
These tests led to Stokes’ law and a different form of viscosity measurement. He tested this theory by putting fluid in a glass tube and measuring how long it took for the fluid to flow a certain distance. Stokes surmised there was some type of internal friction in the fluid causing the different rates of falling. He discovered that the same particle sank at different rates in different fluids. Therefore, this type of viscosity measurement requires an external force in order to be measured.Ībout the same time Poise was performing his tests, an Irishman named Sir George Stokes was dropping particles into fluids and measuring how fast they fell to the bottom. Pascal is a unit of force just like horsepower. The formula for dynamic or absolute viscosity is 1 centipoise (cP) equals 1 millipascal-second (mPa-s). The term dynamic or absolute is used for this viscosity measurement. To make readings easier, centipoise (cP) is preferred for lubricant viscosities. This internal friction is measured by the force needed to make it flow and was given the measurement name of poise. This led him to conclude that different fluids have an internal friction which must be overcome by an external force in order to flow. Poiseuille found that different blood flowed at different speeds through the glass tubes with the same amount of force. This article explains the differences.Īround 1840, a French mathematician named Jean Leonard Marie Poiseuille conducted tests involving the flow of blood through small glass tubes. This resistance is measured by two different methods. The definition of lubricant viscosity is the fluid’s resistance to flow and shear. Viscosity is the utmost characteristic of a lubricant.
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