# Formula of viscosity

viscosity formula = η = F̅/A(shear stress)=Δvx/Δz but i noticed that viscosity depends upon temperature too.Shouldnt there be temperature variable too in the formula ?

• This feels like a case of people using formulas without knowing what they mean. That formula gives the strength of forces due to viscosity. It doesn't calculate the viscosity, which you need a microscopic theory for. – jacob1729 Jun 9 at 13:42
• @jacob1729 then what's the difference between viscosity and force due to it. Isn't viscosity conceptualized as as quantifying the frictional force that arises between adjacent layers of fluid that are in relative motion. – Bhavay Jun 9 at 14:20
• Viscosity is a material property. Given a material, and a detailed enough microscopic theory of it, you can compute its viscosity. This will be temperature dependent. It might also depend on lots of other things. The effect that it has is the formula in your post, but that is completely different from what causes it. – jacob1729 Jun 9 at 15:50

Viscosity is a function of temperature. So, $$F=\frac{F}{A}=\eta(T)\frac{\Delta v}{\Delta x}$$ and $$F(T)=A\eta(T)\frac{\Delta v}{\Delta x}$$
If you know the equation $$\eta = f(T)$$, then use this equation instead.
If you do not know the equation $$\eta = f(T)$$, then stay with given formulas, as they include temperature dependence implicitly.