Gravity. kiloNewtons. *Whoa*, stop there, time for hurting heads! I have a friend, Kyle, who plays football. He's a linebacker and weighs, oddly enough, 225 pounds. Now, for those of you into this sort of thing, that actually turns out to be EXACTLY one kiloNewton, give or take a coupla ounces. Although Kyle is not a climber, he puts up with my jokes about "Kyle units" whenever I show him my climbing gear. "Look!", I say, "this here carabiner can hold 26 Kyles!" A groan usually follows.
So Kyle was asking about climbing and gear, because he's fascinated by all that shiny metal stuff. Turns out he was curious about the ratings on climbing equipment and specifically about how much these wee little things could hold. It was pretty obvious to him that a 10 kN piece should hold ten Kyles attached directly to the ceiling. What Kyle had a little trouble with was the force exerted on a top-rope anchor holding a resting climber with weight fully on the rope. He's OK with 1kN for himself and 1kN for the belayer. He starts frowning whenever I say, "So the ceiling has to hold 2kN (two Kyle's), because there's two things pulling down." Kyle and I still argue about that. Oh, well.
Kyle's head really started to hurt when we talked about falling climbers. During a fall, the rope runs over a carabiner. Carabiners aren't the best pulleys, so the friction of the rope running over the carabiner reduces the force on the anchor from 2x to about 1.67x. This is an important safety factor because it reduces the shock load to the anchor during an actual fall. If you have a dynamic rope rated to 8kN impact force, then the maximum force to the anchor will be roughly 13kN1:    8kN x 1.67 = 13.3kN Additionally, the length of the fall doesn't increase the force to the anchor...it just makes the force last longer.
Since he's not a climber, Kyle got this wicked expression on his face when I explained this all to him in the climbing store. He picked up a Camalot and said, "Hey, this is rated to 10kN." His point, of course, being that the bottoms of cliffs should all be littered with climbers whose gear failed at 13.3kN because the gear was rated at 10kN.
Well, that launched a whole discussion on fall factors2, but Kyle's eyes had glazed over by then, so I ducked his question by explaining that most climbing falls are factor 1 or less and that a factor 1 fall will generate about 5.5kN of impact on the climber (9.2kN to anchor). Kyle laughed and shook his head.   "Yeah, right!" I just shrugged. Somehow, I think Kyle's not going climbing. Whatever. Maybe I should tell him about Yates Screamers. Oh, and Kyle's last name is Newton. Kyle Newton. Huh. Go figure that...