While we are on the subject of physics, I've posted about this before, but never got a real answer. I am a frequent traveler and noticed some passengers using seat belt extenders, but what is the practical limit these restraints can take before they fail? The FAA regulations say that the seats need to survive a 16G crash with a 170 pound passenger, but what happens when the plane unexpectedly overruns the runway while carrying a HAES tour group?  My naive assumption is that the F=M*A can be used as a guide, assuming that the formula works here it would mean that a 340 person could destroy an airline seat in a 8G crash, or the 500 pound person might cause the seat to fail at 5-6G. Once they become a unsecured load the person becomes a projectile capable of doing even more damage to the passengers and cabin around them. Then comes the nightmare of the overwing exits.