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4 Kids, Sports, and Concussion In the 1940s, this realization came to the medical community. Two researchers, named Denny-Brown and Russell, were studying concussion in animals. In order to concuss the animals, they would strike them in the head with a weight attached to a pendulum. The weight would be dropped from various heights. It would swing down and strike the animal in the head. From their experiments, we have learned that if the head is held in place, and not allowed to move after it is struck, there are cuts or lacerations of the scalp, sometimes broken skull bones, and sometimes bleeding in the brain. The brain, however, seems to function properly. The animal is upset and angry, but does not appear stunned, dazed, disoriented, and is seldom knocked unconscious. If, however, the head is free to move after it has been struck, the brain stops functioning properly. The animals often lose consciousness or “get knocked out.” Even when they do not get knocked unconscious, they are clearly off- balance and dazed. This led physicians and scientists to believe that it was not the blow itself that causes a concussion, but rather, the rapid movement of the brain after the blow, the acceleration of the brain. Over time, other medical and scientific research confirmed these findings: the head must accelerate after impact in order for a concussion to occur. This observation led doctors and scientists to conclude that it is the acceleration of the brain that leads to a concussion as opposed to the impact itself. But whether it was linear acceleration or rotational acceleration that led to the injury remained unknown. Around that same time, some other observations were made. The brain consists mostly of water. Perhaps as a result, many of the physical properties of the brain are similar to those of water. For a moment, think about what would happen to a bowl of water with feathers floating on top if you were to slide it along a slippery surface, such as a piece of ice. By sliding it, you would be, in scientific terms, applying a linear acceleration to it. Once the bowl stopped sliding, the water would continue to accelerate toward the front of the bowl, climbing up its frontward surface. The water would then flow down the front surface across the bowl and up the back side of the bowl. This would ulti- mately lead to waves throughout the water. The feathers would bob up and down on top of the waves. But the relative positions of the feathers to one another would remain the same. Each feather would remain in more or less in the same place within the bowl, bobbing up and down on top of the waves until the waves came to a stop. If, however, you were to spin the bowl instead of sliding it in a straight line, feathers would be thrown around the bowl end- ing up in various locations. By spinning it, you would be, in scientific terms, applying a rotational acceleration to it. A similar thought experiment to this was carried out by a physicist named Holburn in the 1940s. In order to follow up on this thought experiment, Holburn made a gelatin model of the brain, a fake brain made of a substance similar to Jello. He put this gelatin brain inside a wax model of a skull. He then spun the skull and brain, or, in scientific terms, he applied a rotational acceleration to the skull and brain. He then cracked open the wax skull and