**posted for Sophie Lederer**
Concussions are an alarmingly frequent injury among football players. Such an injury is caused by a sharp twist or compression of the brain in the skull. Recently, researchers from Simon Fraser University in Canada have created a novel “impact-diverting decal” which is designed to reduce the twisting and compression forces felt by players’ heads in football helmets to reduce concussions. The decal is composed of “micro-engineered layers” of materials that are 1 mm thick and weigh 12 grams. The main purpose of the decal is to reduce the frictional force felt by the helmet when in contact with the impacting surface. In doing so, the frictional force spreads over a larger area, which reduces compression of the brain. This is explained by the concept of Torque, which we have not learned in class yet, but which can be understood from our knowledge of forces and collisions.
T = torque
T = r x F r = displacement vector (from the center of mass to location of force)
F = frictional force
Thinking about this equation, it is understandable how the jelly decal can reduce torque by reducing the frictional force felt by the helmet during a tackle. We can also think about the decal’s effects on forces in terms of momentum.
SF = Dp / Dt
The 1 mm thick jelly decal will increase the time it takes to change the momentum of the player in the tackle, thereby reducing the force felt by the player’s head. For example, let us consider a football player who is 90 kg, and is brought to rest (0 m/s) during a tackle after running with an initial speed of 3.5 m/s.
Dp = (90 kg x 0 m/s) – (90 kg x 3.5 m/s) = - 315 kgm/s
Let us also estimate that this change in momentum occurs over 0.001 seconds without the BrainShield decal, and 0.002 seconds with the decal.
Without the decal: With the decal:
SF = 315 kgm/s / 0.001 s = 315000 N SF = 315 kgm/s / 0.002 s = 157500 N
So, having the jelly decal effectively reduces the force felt by the head during the tackle by increasing the time of impact.
BrainShield was tested on the SFU football team, and the number of reported concussions was reduced from 14 to 4 after one year of use. This success makes sense by understanding the physics involved. The decal is able to reduce both the torque (through reduction in frictional force) and the compression force (by increasing time of contact) during a tackle, which helps prevent injury.