In the rope access industry everything is rated in kn of force. We can directly equate this to 100 kg when looking at working load limits on the slings in which we use to hang off of. Everyone always says you don’t need to know why, you just need to know that it does. I would like a simple way of explaining it to the new people coming into my industry.
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The newton (and by extension the kilonewton) is a unit of force. In case of ropes, it’s important that you know how much force it can take, in case you’re doing something else than just hanging off of it (eg swinging a mass around). In that case, you could calculate the tension in the rope, and pick one that works.
But if you’re just hanging on it, then it’s a lot easier. In that case, the only force we’re worried about, is gravity. So to see why 1kN of force is (roughly) equivalent to 100kg of mass, we need to look at one of Newton’s laws: F=m*a. Force is mass times acceleration. We already know what the maximum force the rope can handle is. And here on Earth, the acceleration due to gravity is around 9.81m/s². It can differ from location to location, but that’s good enough for most cases. So to find the mass that corresponds to the 1000N, we divide that by 9.81. Now, this isn’t all that easy to do when out in the field. So usually, the gravitational acceleration gets rounded to 10. This is less accurate, but more safe. If the rope can hold 1000kN, then it can hold a mass of about 102 kg. So by saying it’s a mass of 100kg, it makes the calculation easier, and since you round the end result down, it doesn’t make it less safe.
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