There are hundreds of ways to sustain an injury like a concussion. (getting hit by an object, falling on the floor, falling off of a tube, etc.) It may be strange to think about, but a concussion is truly caused by a basic physics concept: the law of inertia. Take the example of falling on the floor. When a head makes contact with the floor, the skull will obviously stop traveling in the direction of the floor. The brain, however, will continue moving until acted on by an outside force because it did not make direct contact with the floor. This causes the brain to keep moving until it makes contact with the skull, which causes the concussive energy to flow throughout the brain and ultimately lead to a concussion. So next time you fall off of a tube connected to the back of a speed boat and smack your head against the water at such a force that gives you a concussion, you can blame your misfortune on the fact that your brain is made up of matter and therefore influenced by the law of inertia.