How does 1Kn of force equal 100 kg in weight

Question

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.

In: 1

Answer 1

You have two different things here the force that you can pull on a rope (without breaking it) and what sort of mass would pull with such a force if you attached it to the rope.

A 100 Kg mass would pull on the rope with about a Kilonewton of force.

A Newton is just a different way of saying a force or weight of 1 kilogram times a meter divide by a second squared. (1 N = 1 kg x 1 m / 1 s^2)

A Mass of 1 Kilogram has a different weight depending on where you are exactly, but if you are on earth it usually is somewhere around 9.81 m / s^2 ( It can be as high as 9.83 m / s^2 and as low as 9.78 m / s^2).

If you don’t need super high accuracy using 10 m/s^2 for gravity on Earth is fine and you will err on the side of caution.

This gives you a nice round number like 10 Newtons of force per kilogram of mass.

So 1 Kilonewton is 1000 Newton which works out as the approximate force that a weight of 100 kg would produce here on earth due to gravity. (Really it would be 98.1 kg plus or minus a few hundred gram depending on location but 100 kg seems good enough.)

For traditional American units both force and mass are measured in pounds. This makes this one conversion easier but every other unit conversion more complicated and really messes things up when you need higher accuracy that takes into account that the relations between mass and weight is not the same everywhere)

You can get from Newtons measuring force to Pascal measuring pressure by dividing the force by the area and 1 Pascal is a newton divided by a square meter.

You can also get energy or work measured in Joule by multiplying Newton with a meter instead.

And you can get Power in Watt by multiplying it with a meter per second.