Question

What happens to the lungs when the diaphragm contracts?

Answer 1

Contraction of the diaphragm flattens it, the volume of thoracic cavity increases, pressure inside lungs diminishes and hence air rushes in: we call it breathing in.

Explanation:

During breathing in, the volume of the chest cavity increases due to flattening of diaphragm, and the sternum is also pushed forward due to bucket-handle like movement of ribs.