Along with the head and neck motions that result from a typical impact, there are two components of acceleration involved in head and brain injuries — linear and rotational.
What are linear impact forces?
Linear forces are straight-ahead forces that snap a rider's head violently forward or backward upon impact. Linear acceleration injuries are caused by straight line forces brought about by abrupt deceleration of the brain as it moves through space.
What are rotational impact forces?
In contrast, rotational acceleration injuries are caused by nonlinear forces that twist the brain inside the skull, namely rotational forces. These occur due to impact to the side of a rider's head, violently whipping the rider's head to one side. The brain is most sensitive to rotational motion.
While both rotational and linear forces play a part in nearly every impact to the head, experts believe that rotational forces are far more harmful to the brain.