"Hard" is a understatement. I doubt most people who read this has any knowledge of physics in terms of energy. But simplest put kE=(mv^2)/2

As in, mass and velocity is squared, now this is the reason that every superhero-show is horseshit because if you'd even throw a baseballbat at a 10th of the speed of light, it would superheat everything near it through cheer force of velocity- and mass that it'd literally explode our entire fucking planet.

That's a baseball, at 10th of the speed of light, exploding this entire speck of a planet.

What we're seeing here, is just a rope with the potential-energy of (what I am guessing?) is either a ship, huge anchor, or something very very large. It's not even a billionth of a 10th of the speed of light, but that tension is still strong enough to cleave a man straight in two within a blink of an eye.