(4.19)
	(4.20)

The change in momentum due to collisions of molecules at all speeds is then:

(4.21)

which is equal to the average force dF multiplied by the time interval dt during which it acts (i.e., the impulse), or,

(4.22)

The average pressure p exerted on the surface is given by:

(4.23)

(4.24)

Let,

(4.25)

which is the average value of the squares of the velocities of all molecules.

Therefore,

(4.26)

Here,

(4.27)