Law of Laplace

[Ref: WG21:p588]

 

Law of Laplace

Tension in the wall of a cylinder (T)
= [Transmural pressure (P) x radius] divided by wall thickness (w)

i.e. T = Pr/w

 

Simplifying,

--> T=P.r

OR P=T/r

 

In a sphere,

P = T (1/r1+1/r2)

And r1=r2

--> P = 2T/r

 

Summary

For a cylinder,
T = Pr

For a sphere,
2T = Pr

Implication

• Tension is proportional to radius, if pressure is constant.
• Pressure is inversely proportion to radius, if tension is constant.