Electrowetting and dielectrophoretic actuation are potentially important microfluidic mechanisms for the transport, dispensing, and manipulation of liquid using simple electrode structures patterned on a substrate. These two mechanisms are, respectively, the low- and high-frequency limits of the electromechanical response of an aqueous liquid to an electric field. The Maxwell stress tensor and an RC circuit model are used to develop a simple predictive model for these electromechanics. The model is tested by measuring electric-field-induced pressure changes within an aqueous droplet trapped between two parallel, disk-shaped electrodes immersed in a bath of immiscible, insulating oil. The experiment is an adaptation of Quincke's original bubble method for measuring the dielectric constant of a liquid. For AC voltages lower than similar to100 V-rms, the pressure data largely conform to the square-law predictions of the model. At higher voltages, this square-law behavior is no longer evident, a result consistent with the well-known contact angle saturation effect. Pressure data obtained with DC electric fields are not consistent with either the lowest frequency data (10 Hz) or with the model.