This past semester I took "History of Warfare", a half-year elective that took an in-depth look at all major US wars since WWI. On the last day of the class, we shifted focus to the homefront and talked about mental injuries veterans sustain and how they try and cope after war. One thing that really shocked me was the existence of a fairly recently discovered injury called Traumatic Brain Injury (TBI). What surprised me even more was the way in which this injury was sustained. Essentially, the supersonic winds created by explosions cause the brain to rock inside the skull over a time period of about 3 milliseconds. What is amazing (and very concerning) is the fact that these winds can impact anyone in the blast radius of 1 foot to up to 1 mile. The brain even moves so fast that your body doesn't even know its happening... and because of this it is an injury that over 200,000 living veterans suffer through every day. The symptoms can be compared to CTE in football players and leave veterans feeling "punch drunk" just like the worlds most famous boxers. The physics come into play when the blast wind hits the body. First off, the shock of the wind is transmitted to the body as a wave of energy and any surface (like a skull or helmet) can reflect the wave, meaning it can impact the brain 3-5 times per explosion. In WWI, when the symptoms were first being documented, leading doctors thought the kinetic energy of the blast traveled up the spinal column and into the brain. Now, there a are theories that go so far as to say shock waves of kinetic energy can reach the brain through the bloodstream. Although the injury is very serious, it is interesting from a physics perspective to think about the energy transfer happening between those billions of particles through the bloodstream, spinal cord or skull.
P.S.- Anybody with a free period should see if they could get into this class for the new semester. Its an eye-opening class that was definitely a great choice of an elective.