This is the lung model. The balloons represent lungs; the pipe represents the trachea the elastic membrane represents the diaphragm, although it is poor representation of it since it starts out flat in the model, but the diaphragm is dome-shaped when relaxed. The jar represents the ribcage, and it is also poor representation of it since the jar does not move during respiration, and the ribcage does. When the membrane is stretched, the volume of the chest cavity increases, and the pressure of the chest cavity decreases.