**[Terminology] Laplace equation**

Laplace equation describes the pressure difference on both sides of the curved liquid surface, which is related to the surface tension of the liquid and the radius of curvature of the liquid surface.

The equation is as follows:

Δp=γ(1/R_{1} + 1/R_{2})

Δp: Laplace pressure; γ: surface tension of liquid; R_{1}, R_{2}: principal radius of curvature.

When the liquid surface is spherical, Δp=2γ/R, R is spherical radius.

In general, curvature of convex surface is positive, curvature of concave surface is negative, and curvature of plane is 0.