100 lbs of drag? Really? Chain running physics Recently came across this video of an endurance technique involving the strapping of a 100lb chain to one's back and running along the grass dragging it behind. What is the true force experienced by the runner?
 A: The chain looks pretty long, only a meter or so is actually in the air. The gravitational force on the runner by the chain is not that big. The runner is bulled back/down in the angle that the chain attaches to the back. The chain cannot convey any torque or transversal force. So there are only a few kilograms of weight directly pulling on the runner.
A lot of force is probably the acceleration of the chain. The runner cannot keep his back at a steady velocity, it will move back and forward. Therefore there is a certain tug on the chain. The chain will be tugged forward, which is acceleration. Then it will quickly come to a rest again in the grass.
Do a thought experiment: If you are on ice skates gliding forward and the chain gliding on the ice, it would not be much work to pull the chain around. The friction on the grass is the problem. It is hard to quantify the force needed.
So although I am a to-be theoretician, I would suggest to just do a measurement with a force meter. It would probably be best to have a good resolution in time such that you can get the time dependent $F(t)$ and can then properly average over it.
