Method and apparatus for modulating the direction and magnitude of the Casimir force between two bodies. In accordance with the illustrative embodiment, a repulsive Casimir force is generated by placing two bodies in near-proximity to one another. For one of the bodies, dielectric properties predominate; for the other, magnetic properties predominate. The arrangement further includes a device that alters the dielectric or magnetic properties of the bodies. By altering the dielectric or magnetic properties, the repulsive Casimir force can be made to decrease, then vanish, then reappear as an attractive force. Modulating the Casimir force in such a manner can be used to control stiction in MEMS devices and to accelerate particles, among many other applications.