We know that in physics, boyle's Law describes the relationship between volume and pressure when the temperature is held constant. And because our body is at a constant temperature of 36.7 degrees Celsius, we can assume that this obeys Boil Law, meaning the temperature is constant. Now, Boyle's Law tells us that the pressure multiplied by the volume is equal to a constant value. And that gives us an inverse relationship between pressure and volume. So as the volume increases inside the intraplural space, by Boils Law, the pressure must decrease. Now, what exactly is the pressure inside the lungs?