Tag: option b: engineering physics

To reduce the fluid  friction body of an Aeroplane is streamlined .

Velocity gradient $=\dfrac{dv}{dx}$
so dimensions of velocity gradient is $\dfrac{[LT^{-1}]}{[L]}=[T^{-1}]$

The viscous drag force can be written as below:
$F =  \eta \ A \ (\cfrac{dV}{dX})$ where, F is viscous drag force (or tangential force)
$\eta$ is coefficient of viscosity
$A$ is surface area of layers in contact
$\dfrac{dV}{dX} $ is velocity gradient
$\eta$ is property of liquid.
So, we can see that drag is directly proportional to the velocity gradient, surface area and nature of liquid. Drag force acts in opposite direction of liquid flow. 

A fluid that has no resistance to shear stress between its layers is known as an ideal fluid.(Definition).Hence ideal fluid  has zero viscosity.

Viscosity depends of mass of body, temperature, velocity and density.
Where as friction depends only on normal reaction.

Due to surface tension of oil capillary rise can be seen in cotton wick which makes lamp to burn.

If angle of contact is acute, liquid rises in a capillary tube whereas if angle of contact is obtuse, liquid is depressed in a capillary tube.