Shock Wave- The rapid expansion if air caused by the sudden and extreme heating of the air in a lightning channel during a return stroke. The shock wave continues outward for a few feet, moving faster than the speed of sound, and then slows to a sound wave, heard as thunder. The shock wave from an extremely close lightning strike can knock a person off his/her feet, and cause hearing damage and/or other injury. These shock waves can also damage objects directly struck or nearby objects. (See Thunder)