# What is the pressure in a microscopic scale?

1. ### omar.abosamra

7
i have took a basic course in fluid mechanics:
Bernoulli equation states that:
P + (1/2)*ρ*v^2 + ρ*g*h = constant
where P is the pressure , ρ is the density , g is the garvitational acceleration and h is the distance from the center of the earth , and that constant is our reference.

that means if thier was a tube carrying a stream of fluid with velocity V , the pressure on the wall of the tube would be:
(1/2)*ρ*v^2 + ρ*g*h + constant

what does that mean in a microscopic scale ? what happen with the interaction of the molecules of the wall and the fluid ?

and can their exist pressure inside the fluid due to the viscosity of the fluid ? if we assume that every layer moves with a speed different that the next layer due to viscosity? and if so , how would the pressure affect the stream ?

2. ### Studiot

The 'fluid particles' ( also called fluid elements) considered in fluid mechanics are not the molecules of the fluid.

In fact fluid mechanics does not consider molecules at all. The particles just have to be small enough for the analysis concerned. The fluid is taken as continuously divisible down to whatever scale is required.

Pressure has no meaning at a molecular (or smaller) scale.