![]() The first step, of course, is to establish what we mean when we talk about acceleration as a means of talking about force. ![]() I got involved in discussion of g-forces this week in a completely different context, but having spent some time trying to sort it all out, I thought I'd devote this week's Football Physics post to some everyday (-ish) examples of different sorts of acceleration, to help put things in perspective. Damage from acceleration depends on the magnitude of the acceleration, the direction, the duration, and probably some individual variation in brain structure and so on. It doesn't help that the threshold for what acceleration causes damage is still fairly ill-defined- necessarily, because it involves messy biological systems, rather than the frictionless spheres beloved of physicists. This helps, sort of, but as more numbers get thrown around, it can get a little confusing- this tackle was five gees, that one twenty-seven, and so on. (There's a good discussion of this in a sports context in this paper from the Journal of Athletic Training). So, people colloquially talk about a force of some number of "gee"s, meaning that the resulting acceleration was that many times the acceleration of a falling object. This constant acceleration provides a basis of comparison for thinking about forces- since what we're actually sensing when we experience a force is the acceleration, and everybody experiences a constant force of gravity, we can attempt to give a more intuitive sense of the forces involved in football collisions (or anything else involving significant acceleration) by expressing the resulting acceleration in terms of the constant acceleration of a falling object. #High g force training freeThe repeated "per second" reflects the fact that this is a change in velocity, not position- after one second of free fall, a dropped object will be moving at 9.8 m/s (about the speed of a full-out sprint), but it will have covered a distance of 4.9 meters. The term comes from the fact that near the surface of the Earth, the force of gravity causes any dropped object to fall at a constant rate of 9.8 meters per second per second (32 feet per second per second if you prefer american units), traditionally given the symbol " g". ![]() It's all but impossible to talk about the issue of head injuries in the NFL without "g-forces" coming up. ![]()
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