Viscosity reflects the internal friction of a lubricant, and is the index of its lubricity and liquidity.

Viscosity index indicates how the viscosity of a lubricant changes with the temperature change. It shows the relation between viscosity and temperature.

Apparent dynamic viscosity also reflects the resistance of a lubricant against flow, but has another special test method. According to definition of tribology ”It is tested under a certain shear rate and appears in the unit of mPas”.

*      Is the concept “viscosity” more widely used than “apparent dynamic viscosity”?

Let’s express this in more descriptive language instead of physical calculation, “Viscosity” is the internal resistance of a specific liquid, while “apparent dynamic viscosity” means the final overall viscosity a lubricant shows as a whole.

Especially when a liquid state lubricant becomes a grease, the original viscosity of liquid state can not be truly reflected and needs another way of measurement.

*      Can “viscosity” substitute the latter under some circumstances?

Yes, the two are related. Grease made by higher “viscosity” base oil will also have higher “apparent dynamic viscosity”. Only with liquid state can the two values have linear relation and the latter can be substituted by the former.

*      “Apparent dynamic viscosity” has its way of measurement. And, how is “viscosity” measured?

"Viscosity", which is the liquidity of a fluid, is measured by viscometer. It measures the flow time of a defined amount of liquid sample through a standard instrument.

*      What properties do the two concepts define?

         "Viscosity" defines the liquidity.

"Apparent dynamic viscosity" defines the force (shear force) required under certain driving speed (shear rate).