hey. i found this online calculator

http://www.myoan.net/climbart/climbforcecal.html

but i think its mistaken. if i simulate a fall with a 80 kg climber, that falls 1.5 meters for a factor 2 fall with dinamic rope, i get a shock of 9 kN on the climber.

then i change the 1.5 meters for 15 meters and i get the same 9 kN. this doesnt sounds right, since obviously if the lenght of the fall increases, the speed increases, right??

so does anyone knows of a good, accurate calculator??

thanx!!

thanx. i did the force calculations for a fall some time ago, considering fall factor, lenght of rope used, weight of climber, and elongation of rope. i think those are the variables needed. or do you need something else?? i wanted to see if my math was correct...

My understanding is that, theoretically, the peak force to the climber will remain the same for factor 2 falls of ANY distance, assuming a constant Young's modulus.

This is primarily due to the fact that the longer the fall, the more rope available to stretch. While shorter falls are slower, they have less rope out.

Well, that's all you need according to the formula in RG's "The Standard Equation for Impact Force"
http://www.rockclimbing.com/...ent;postatt_id=2957;

Of course there are a lot of variables when it comes to the actual numbers in an actual fall... but that's the basic formula FWIW.

thats what i thought about a possible reason for the numbers i got on the calculator i posted. however, it doesnt seems logical to me. how can a .1 meter and a 15 meter fall give the same numbers?? i mean, most probably i wouldnt mind having a factor 2 fall of .1 meters (3 inches) on static rope. while a 2 meter fall of the same rope would probably break my back..... and the calculator gives the same numbers for both falls...

Same peak force for short & long falls - but in a longer fall, the duration of the force is longer (if you plotted force vs. time, the area under the curve would be larger for a longer fall).

At least for the first approximation.

so do you think the calculator i originally posted is correct???

because if it is, it says that the maximum peak force ever experienced by a climber is 9 kN with dinamic rope.... of course the impact as seen on the anchor is greater, since the belay also recieves a force and the anchors gets both.... i read somewhere that the anchor suffers about 1.66 times the force felt by the climber, that would be about 15 kN for a factor 2 fall.... is that correct?? it seems weird to me.

thats what i thought about a possible reason for the numbers i got on the calculator i posted. however, it doesnt seems logical to me. how can a .1 meter and a 15 meter fall give the same numbers?? i mean, most probably i wouldnt mind having a factor 2 fall of .1 meters (3 inches) on static rope. while a 2 meter fall of the same rope would probably break my back..... and the calculator gives the same numbers for both falls...

so do you think the calculator i originally posted is correct???

because if it is, it says that the maximum peak force ever experienced by a climber is 9 kN with dinamic rope....

of course the impact as seen on the anchor is greater, since the belay also recieves a force and the anchors gets both.... i read somewhere that the anchor suffers about 1.66 times the force felt by the climber, that would be about 15 kN for a factor 2 fall.... is that correct?? it seems weird to me.

That calculator is a piece. It says a 10m fall on 10m of rope is a factor 1.5 fall. ummm no its not...

Yes, the numbers are the same; if you took a solid weight attached solidly to the anchor, the real world numbers might be the same as well. But in the real world, with knots, harnesses, soft bodies, the actual effect you feel could be much different. In a 30' fall, your whole body is falling. In 3", if you were hunched over, you body may have straightened out and your head may never have moved.

At any rate, the numbers the calc generated are correct as the only FF it can work with is FF2, it doesn't calculate any other FF properly.

thats what i was thinking. to work with other fall factors, it should know the lenght of rope used, right?? because its not the same falling 3 meters above the 10th protection, where you could have have 23 meters of rope, than falling 3 meters above the second pro, where (assuming you dont deck) you have just 9 meters to arrest the exact same fall...

No, the forces for a 10' FF1.5 fall are the same for a 500' FF1.5 fall... theoretically. If you know the fall factor, it doesn't matter how much rope is out as the numbers are the same... theoretically.

Now, what you actually feel when you fall depends on a lot of other variables. A 3" FF2 fall would, in theory, produce the same forces as a 30' FF2 fall, but because the fall is so small, all the force reducing variables play a bigger role, so the net forces felt are could be much less. So you might not feel a 3" fall where you would certainly feel a 30" fall. That's where the Fall Force calculators fail, there are too many other variables to predict real world numbers. But they can give a ballpark figure all else being equal.

The moan.net calculator fails because it can't calculate fall factor properly. It does work with FF2, but as USNavy said, it can't figure out anything below a FF2 properly so the numbers it generates are useless (or slightly more useless than a calculator that works).

thanx. unfortunately at work i cannot open .pdfs but ill try it at home.

and im glad to know i included the variables needed. when i can look at the formula i will see if i used them correctly...

If you included both the fall factor and the length of rope in your calculation, then your formula is either wrong or very advanced.

Jay

i believe there is where the calculator fails, since it doesnt asks for the amount of rope you have on the system, so it cannot calculate the fall factor correctly. you can have 3 meters from your last pro, but what is under the pro also plays a huge part in arresting the fall....

well, it was not just one formula. i used the lenght of the rope to calculate the fall factor, and also to calculate the elongation (i assumed 30% of all the rope used). this was to account for the fact that, if i have a factor 2 fall on 1 meter of rope, i will start at 1 meter above the anchor but i will end 1.3 meters below it, because of the elongation. i know its just an approximation that does not takes into account several things, such as the desacceleration during those 30 cm.... because the body would be accelerating for 2 meters and then the acceleration would decrease until it reaches 0 and the rope suffers maximum elongation. but i think taking all that into account would be really difficult, as most probably the desacceleration wouldnt be at a constant rate...

No, there's no need since they ask for the "Length of rope" and "distance from last anchor", fall factor is easily calculated as

("Distance from last anchor" x 2) / "length of rope"

However, this is the incorrect formula they are using.

("Distance from last anchor" + "Length of rope")/ "Length of rope"

That ends up calculating FF higher than it should be.

how do you know they are using that formula instead of the first and correct one you mention??

So, are you treating elongation as a constant 30%, regardless of the fall factor?

Jay