Final answer:
Inhalation is an active process involving the contraction of the diaphragm and other muscles, allowing air to flow into the lungs. Exhalation is typically a passive process due to the elasticity of the lungs, forcing air out through increased air pressure. Forced breathing involves additional muscle contractions to manipulate breathing during activities like exercise or singing.
Step-by-step explanation:
Inhaling is an active process that mainly results from the contraction of the diaphragm, a large muscle below the lungs. When the diaphragm contracts, the thoracic cavity expands and the abdomen is pushed downward, allowing outside air to flow into the lungs. Other muscles such as the external intercostal muscles between the ribs also contribute to inhalation, especially when taking a deep breath.
Exhaling, on the other hand, is typically a passive process that occurs mainly due to the elasticity of the lungs. The diaphragm relaxes, moving upward and decreasing the thoracic volume. This increase in air pressure inside the lungs forces the air out, similar to how air rushes out of a balloon when it is released. If forced exhalation is required, internal intercostal and abdominal muscles can assist in moving the air out of the lungs.