Football Concussions

* I have suspected for years that the modern football helmet is designed to protect the scalp and skull but to promote concussions. Modern helmet composition is described in: Types of Padding in Football Helmets . A modern helmet has a rigid outer shell, the space between the shell and head being filled mostly with stiff foam. This spreads the accelerating force from an outside blow over a wide scalp surface, defending the scalp and skull from deformation but with little dissipation or damping of the momentum.
* This design transfers linear and shearing momentum from an external blow to the skull as efficiently and quickly as possible, throwing the brain against the skull almost as much as possible and spinning the skull about the brain almost as much as possible (owing to the density difference between brain and cerebrosponal fluid and the lubricating effect of the cerebrospinal fluid between skull and brain). Thus the brain is mechanically deformed by bouncing in the skull and by shearing between brain and skull.
* In a rationally designed helmet, the shell itself would absorb as much of the blow as possible and it would transfer momentum from shell to skull as slowly as possible, thereby minimizing linear and shearing accelerations of the skull. Specifically, the shell would be flexible, resilient, tough and slippery. Its stiffness would be just sufficient to avoid striking the scalp under the maximal blow that might occur in a game, by collision with another helmet or a knee or the ground. The main material between the shell and scalp would be a specially designed bubble wrap, one layer with large loosely filled and crowded bubbles or several layers with smaller loosely filled and crowded bubbles. This design would allow the shell to deform, hence to absorb a blow with slowest possible transmission of linear and angular momentums from an outside blow to the scalp, hence to the skull and brain. Ideally, the hardest blow would bend the shell inward as close to the scalp as possible without hitting it.