Final answer:
The driving force for the movement of air into the lungs is the pressure gradient. When we inhale, the expansion of the thoracic cavity creates negative pressure in the lungs, causing air to diffuse into the lungs.
Step-by-step explanation:
The driving force for the movement of air into the lungs is the pressure gradient. Air flows from an area of higher pressure to an area of lower pressure. When we inhale, the diaphragm and intercostal muscles contract, expanding the thoracic cavity and creating negative pressure in the lungs. This causes air to diffuse into the lungs.