Laplace's equation defines the relationship between the pressure gradient across a closed elastic membrane or liquid film sphere and the tension in the membrane or film. The equation indicates that the pressure inside a spherical surface is always greater than the pressure outside, but that the difference decreases to zero as the radius becomes infinite (when the surface is flat). In contrast, the pressure difference increases if the radius becomes smaller and tends to infinity as r tends to zero.The Laplace equation is used to predict sub-bandage pressure.It is derived from a formula described independently by Thomas Young (1773-1829) and by Pierre Simon de Laplace (1749-1827) in 1805.
P=2T/R
where:
• P = Transpulmonary pressure
• R = radius of an alveolus
• T = Tension in wall of alveolus
The Laplace law introduces an equation that can determine the pressure of liquid, when the liquid is in a droplet configuration. Two equations are derived for two different types of droplets; droplet, and bubble shapes. These shapes of moisture have an impact on the lining on the lungs and, therefore has an influence on the pressure volume of the lungs. This influence is the attractive forces between adjacent molecules if the liquid are much stronger than those between the liquid and gas. This results in the liquid surface area becoming as small as possible.
Thereby, the liquid sphere will attain the smallest surface area of a given volume, and producing a pressure that can be measured by Laplace law.
The Following Equations apply:
P = 2T/r (drop) P = 4T/r (bubble)