text: The pressure inside an ideal spherical bubble can be derived from thermodynamic free energy considerations. The above free energy can be written as:
  where  is the pressure difference between the inside (A) and outside (B) of the bubble, and  is the bubble volume. In equilibrium, , and so,
  For a spherical bubble, the volume and surface area are given simply by
  and
  Substituting these relations into the previous expression, we find
  which is equivalent to the Young–Laplace equation when .