HELMET NEWS ARTICLE FOR NOVEMBER 2004
THE FOOTBALL HELMET, PART 3
By Dr. Ken
Past articles in the HELMET NEWS section of HELMET HUT have given what I believe are complete descriptions of the typical football helmet and some of the evolution in its construction. The average fan or helmet aficionado can think of the helmet as a two-part design: the outer shell and the inner lining. For our purposes, the suspension helmets of the 1950s to 1970s qualify as an “inner lining”. Both parts are necessary to attenuate a blow to the head or one delivered by the player to another combatant. Each “contact” or hit applies a certain amount of pressure to the point that is being contacted. Pressure is a function of the degree of force (which itself is a function of mass and speed) as it is applied to a specific surface area. The equation is simple: applied force to a smaller area, the greater the pressure; the same applied force to a larger area, the less the pressure. If the area remains the same, we can reduce the pressure by contacting it with reduced force. On the field, no player wants to reduce their force, this is a given! Thus, to increase player safety, the goal would be to increase the surface area that the force is applied to.
As contact to a player’s helmet is made, their helmet, and the head inside of that helmet, is accelerated. Force has been applied to the helmet and this results in pressure that is now applied
My university physics professor always used the example (at least once or twice a semester for approximately twenty years) of taking a nail and preparing to hammer it into a two-by-four board. Because the nail has a pointed end, the force of the hammer is distributed over a small area, allowing for a great deal of pressure. A flat-headed nail hit with the same amount of force would not have the same pressure applied to the head of the nail and thus would not penetrate the wood at the same to the point of contact. That’s why nails have points!
The helmet’s outer surface distributes the pressure over a wider area than that of the initial or
actual contact. The hard plastic of the helmet is rigid and serves to transfer
the force of the blow as a single unit. If it were of a soft material, the
pressure would be created at the point of initial contact, indenting the
helmet and focusing the pressure in a relatively small area. By distributing
the force over a much wider area, we have reduced the pressure and thus, the
potential risk of injury. Many players wax their helmets prior to a game to
reduce the time of contact and the shape of the helmet helps the player to
“glance off of” the blow as well as distribute it over a wider area.