The air in a house is maintained at 72°F. The air outside the house is at - 20°F. What is the difference in the density of the air between the inside and the outside of the house? There are always small passages where air can infiltrate into or from a house even if extreme care is taken to seal all those passages. Explain what the air particles do even if the outside air is perfectly motionless. See Fig. 2.38.
Figure 2.28