Question

derive an expression for formula of viscous force

Answer 1

For viscous drag, the formula for the force is,

F=±ηA∇uF=±ηA∇u

where ηη is the viscosity coefficient, AA the area and ∇u∇u the velocity gradient

Answer 2

$\large{\underline{\rm{Viscosity:-}}}$

• Frictional force acting between different layers of fluid is known as Viscous force and this property of liquid is called viscosity.

$\large{\underline{\rm{Velocity\: Gradient::-}}}$

• Gradual change in velocity with respect to distance is known as velocity gradient. ∆v/∆x

$\large{\underline{\textrm{Derivation of formula of viscous force:-}}}$

→ F ≈ ∆v/∆x

→ F ≈ A

→ F ≈ A∆v/∆x

→ F = -μ A∆V/∆x

• where μ is the coefficient of viscosity
• It's SI unit is kgm-¹s-¹
• Its CGS unit is Poise. 1 poise = 1/10 k g m-¹ sec-¹