“…As a result, for any point on the droplet surface we can write a force balance
where the friction force K = − GṘ ,is linear in the surface velocity field Ṙ and G is a linear operator that does not depend on v , since the Stokes equations are linear in the fluid velocity field v . 32,33 The force
derives from the droplet free energy, as we explain in Section 2.2, and provides the Laplace pressure, Young's force at the contact line, and constraint forces. Finally, F governs the dynamics induced by deforming substrates.…”