The harm may occur just before the neck jerks back and forward.
You're waiting at a stoplight when it changes from red to green. You hesitate and then, out of the blue, crunch! — you feel the impact of a car colliding with yours from behind. Your head jerks back, and then snaps forward. It's whiplash.
In technical terms, whiplash refers to the sudden transfer of energy that causes the structures of your neck to abruptly straighten and bend beyond their normal range of motion, potentially resulting in an injury. A car accident is the most common scenario, but it's not the only one. Many kinds of falls, the jerking movement of amusement park rides, and blows to the face can also create the whiplash motion and its related injuries.