Energy: you can't destroy it, but you can certainly waste it. That's what most motorized vehicles do, including trains. Usually, the energy generated when you stop a moving vehicle is dissipated as heat, and is lost to the atmosphere.
With GE's ecomagination you can capture and store that energy, then reuse it. Watch the video to see a simple illustration of the physics behind dynamic braking. Keep in mind an object's force is measured in newtons, using the equation force = Mass x Acceleration.
via The Presurfer blog