Electrostatic pressure ($p_e=\mathbf{E}\cdot \mathbf{D}/2$)

The outward normal electric traction on an equipotential conductor adjoining a linear isotropic dielectric, for the ideal normal-field configuration, is $p_e=ϵE_n^2/2=\mathbf{E}\cdot \mathbf{D}/2$. Integrating this normal traction over a surface gives the electric force. It is a field-stress contribution; mechanical pressure and dielectric boundary conditions must be included when determining an actual fluid-interface equilibrium.