11. So, what is lost is the work done by radiation pressure . 12. Radiation is the working fluid, and the piston is driven by radiation pressure . 13. Finally, other forces such as radiation pressure and collisions also result in drifts. 14. While rather small in comparison to other forces, the radiation pressure force is inexorable. 15. "' Radiation pressure "'is the pressure exerted upon any surface exposed to electromagnetic radiation. 16. The articles on radiation pressure and solar sail should contain more information about that. 17. :Moreover, radiation pressure is a classical effect of electrodynamics that doesn't even require photons. 18. Solar radiation pressure is exerted by solar radiation on objects within the solar system. 19. If the luminosity exceeds the Eddington limit, then the radiation pressure drives an outflow. 20. Solar sails use radiation pressure in a way to achieve a desired propulsive force.