When I am abseiling, the rope is initially hard to feed through my braking device - if I take my hands away from the rope, I get stuck in mid-air.
However, as I am getting lower, it gradually gets easier, until at some point the rope starts running by itself. Now, if I took my hands away from the rope (thought experiment - imagine I have no backup braking device), I would accelerate down and hit the ground very hard.
Why is this so? The rope is vertical, and I don't touch any wall, and yet it somehow matters whether I am situated high or low on the rope.
I am abseiling on a static rope, the height is 60 meters. Just to make it clear - the wall is absolutely vertical, and then somewhat overhanging, so the wall doesn't hinder my progress in any way.