Heat and Thermodynamics

4.9 Collisions with a Solid Boundary: Pressure Exerted by a Gas Introducing Mean Free Path Concept

In the kinetic theory of gases, it is supposed that the number density υ of the molecules is constant throughout the mass of the gas in equilibrium at constant temperature and the directions of motion of molecules are uniformly distributed in space.

To find the number of collisions per second on an element of area ds of the wall and there from the pressure exerted by the gas, we take a small volume dv of the gas at a distance r from the centre of the element ds considered on the xy plane, the radius vector r to dv from the centre of ds making an angle θ with the normal to ds (i.e., z axis) as shown in Figure 4.25.

 

 

Fig. 4.25 Illustration of ...