Question

Qualitatively explain the microscopic origin of air resistance and why the magnitude of air resistance scales the way it does with the density of the fluid and the speed and cross sectional area of an object (e.g., What is happening at the microscopic scale that makes the magnitude of air resistance increase for larger objects?)

Answer 1

The air resistance we see at the macroscopic level is due to particles of air at microscopic level hitting with the moving object

As the speed of the object increases that means number of particles which are hitting increases and hence the resistance increases

Also as the cross sectional area increases then also the particles strike larger area and hence larger is the force

Density of the fluid essentially means the number of particles present per unit volume thus increasing density will also increase air resistance