Mechanics refers to the study of mechanical (as opposed to chemical or biological) aspects of breathing, namely the interaction of pressure, volume, and air flow within the respiratory system.
The graph (shown below) will show you where we are in the breathing cycle. Watch the red ball as it moves through the inspiration and expiration cycle. The scale at the lower right correlates pressure changes with the colors used in the illustration. Watch the arrows representing alveolar and pleural pressure as they move.
In this model, purple indicates subatmospheric (negative) pressures, and green greater-than-atmospheric (positive) pressures; the more intense the color, the farther it is from atmospheric pressure, the paler, the closer to atmospheric pressure.
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