I don’t need a physics degree to climb do I?
No but understanding the forces involved with climbing is very important. It is important for understanding the equipment we are using so we know when to use what, It is also important to be able to understand the technical manuals that come with your equipment so you know what the gear can do and when to retire it. And it will be useful so you know what I am on about when I talk about forces throughout the series.
Force is measured in Newtons, or for larger forces (like in Climbing), Kilonewtons(kN). So if a climber had a mass of 100kg (Approx 15stone) then that climber hanging on a rope would be exerting 1 Kilonewton(kN) on the rope and anchor just through the earth’s gravity. If the climber were to ascend the rope, the force could go up to 2kN, the mass of the climber hasn’t changed but the force pulling down on the anchors has. A climber, top roping, would normally produce a maximum of 2-3kN if he or she was to fall. These farces aren’t that great in the world of climbing, the interesting and somewhat more important thing is what is called a fall factor.
What is a Fall Factor?
The fall factor is a number that you can work out to work out the force generated on your equipment during a fall. The maximum a fall factor can ever be is 2.
So how do I work this out?
The Fall Factor is determined by the length of the fall and the amount of rope paid out (amount of rope that the climber falls onto). The equation (don’t worry it’s not that bad!) is:
Length of fall / Rope paid out
So if you fell 10metres on to 10metres of rope your fall factor would be 1, this is still a pretty high fall factor and can cause serious injury and even gear failure.
A fall of 20metres on to 10metres of rope (falling down past the belayer) your fall factor would be 2, this is the maximum you should be able to get in a climbing environment. A fall factor of 2 is very serious, It can cause very serious internal injuries and has a large potential for gear failure and weakened rope.
The fall factor equation does not allow for friction in the system (rope rubbing on carabiners and rock), or dynamic belaying so it can be a lot less than this simple maths determines. It can be worked out but it is not easy by any means.
How can I reduce the fall factor?
The fall factor can be reduced in many ways, the most important being by placing runners(bits of gear in the rock), this shortens your fall so as to reduce the fall factor. Even as soon as you leave a stance (where a belayer stands halfway up a cliff) you should place a bit of gear to stop the fall factor being two, at very least thread it through a bit of bomber(very good) gear on the stance.
Another way to make the fall factor smaller is to do something called dynamic belaying where the belayer attempts prolong the fall and making the climber come to a stop more slowly therefore reducing the force on the gear. This is a topic I hope to cover in the future.
So why does this matter?
This matters because if you understand the principle of fall factors then you can make an effort to reduce the fall factor when climbing using the techniques above, therefore hopefully preventing gear failure and injury.
What forces can my gear take?
Below is a table of the forces that typical climbing equipment can endure. Always check manufacturers guide.
| Equipment | Strength | Dyneema Sling | 22kN | Typical Karabiner | Gate Closed: 24kN | Micro nut | 2-4kN | No.1 Nut | 7kN | No.9 Nut | 10kN | Cam | 10-14kN | Micro Cam | 3-6kN | Harness | Must hold 15kN for 3 minutes |
A typical climbing fall (less than Fall Factor 1) generally has a maximum force of 7kN and in most cases is no more than around 4-5kN, So apart from the micro gear, it will all hold your fall just fine. In a high impact fall (over FF1) of around 12kN some of the smaller gear could start to break. 12kN is the maximum amount of force that can happen on a dynamic climbing rope, this is because standards make manufacturers design their ropes so that they stretch enough to minimise the shock. (note: these standards are for a 80kg object, heavy climbers could increase the max force slightly). Another thing to bear in mind is that falls with force of 10kN and over will cause your body some serious damage.
So hopefully you see the importance of knowing what the gear you use can do and how to minimise it.