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shu2kill


Apr 26, 2010, 6:59 AM
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online force calculator
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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!!


qtm


Apr 26, 2010, 7:06 AM
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shu2kill wrote:
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!!

You're right, that one doesn't work right. I couldn't find any other, so I wrote one myself but it's not online. Jay wrote one that was much prettier than mine, don't know if he put it online.

It's relatively easy to do with an excel spreadsheet. I'll look around to see if I can find it.

OK, here's the formula.
COL A = Rope KN
COL B = Fall Factor
COL C = Weight in LB
COL D = KN on climber

=(C2 * 0.4536 * 0.0098) + SQRT((C2 * 0.4536 * 0.0098)^2 + (((A2*(A2-1.568))/1.396)*(C2 * 0.4536 * 0.0098)*B2))

You have to manually calculate the FF.


(This post was edited by qtm on Apr 26, 2010, 7:19 AM)


shu2kill


Apr 26, 2010, 7:22 AM
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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...


shoo


Apr 26, 2010, 7:29 AM
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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.


qtm


Apr 26, 2010, 7:38 AM
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shu2kill wrote:
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...

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.


shu2kill


Apr 26, 2010, 7:45 AM
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shoo wrote:
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.

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...


shu2kill


Apr 26, 2010, 7:47 AM
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qtm wrote:
shu2kill wrote:
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...

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.

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...


bill413


Apr 26, 2010, 7:55 AM
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shu2kill wrote:
shoo wrote:
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.

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.


shu2kill


Apr 26, 2010, 8:03 AM
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bill413 wrote:
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.


USnavy


Apr 26, 2010, 8:19 AM
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shu2kill wrote:
bill413 wrote:
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.
That calculator is a piece. It says a 10m fall on 10m of rope is a factor 1.5 fall. ummm no its not...


(This post was edited by USnavy on Apr 26, 2010, 8:23 AM)


qtm


Apr 26, 2010, 8:20 AM
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shu2kill wrote:
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...

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.


shoo


Apr 26, 2010, 8:25 AM
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shu2kill wrote:
bill413 wrote:
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....

I can't verify whether it is correct. Only that, from the information you have given, we can't say it's incorrect.

If the stretch properties of the rope dictate that a factor 2 fall of any distance will produce 9kn of force to the climber, then yes, the maximum force to the climber will be 9kN.

9kN is pretty typical of a dynamic climbing rope.

So essentially, yes.

shu2kill wrote:
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.

No.

In the case of a factor 2 fall, assuming a perfectly static belay directly off the anchor, the anchor and the climber will receive exactly the same force during a fall.

In the case of a slingshot (top-rope or redirected belay), the anchor will theoretically receive 2x the force to the climber. Accounting for some friction, the more realistic force would be somewhere lower. The 1.66x sounds reasonable to me, but I can't back that up with numbers. Every situation will be different.


shoo


Apr 26, 2010, 8:30 AM
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USnavy wrote:
That calculator is a piece. It says a 10m fall on 10m of rope is a factor 1.5 fall. ummm no its not...

You're right! What a piece of crap.


USnavy


Apr 26, 2010, 8:36 AM
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Petzl use to have a semi-bad ass calculator on their website called the fall simulator. It was a lot more detailed and accurate then the POS referenced in this topic. I canít see to find it though. :( I think they took it off their site.


shu2kill


Apr 26, 2010, 8:36 AM
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qtm wrote:


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...


qtm


Apr 26, 2010, 8:47 AM
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shu2kill wrote:
qtm wrote:


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).


hafilax


Apr 26, 2010, 9:09 AM
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Petzl probably took it down because it's probably more misleading than useful. OTOH if you like the Petzl one, I've got a model based on a spherical cow that will solve the world's hunger problems.


shu2kill


Apr 26, 2010, 9:11 AM
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qtm wrote:
shu2kill wrote:
qtm wrote:


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).

well, yes, if FF is the same, the force is the same. but notice what i said, i didnt mention fall factor, but fall distance:

....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...

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....


(This post was edited by shu2kill on Apr 26, 2010, 9:49 AM)


jt512


Apr 26, 2010, 10:25 AM
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shu2kill wrote:
qtm wrote:
shu2kill wrote:
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...

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.

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


shu2kill


Apr 26, 2010, 10:31 AM
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jt512 wrote:
shu2kill wrote:
qtm wrote:
shu2kill wrote:
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...

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.

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

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...


qtm


Apr 26, 2010, 10:34 AM
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shu2kill wrote:
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....

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.


jt512


Apr 26, 2010, 10:51 AM
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shu2kill wrote:
jt512 wrote:
shu2kill wrote:
qtm wrote:
shu2kill wrote:
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...

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.

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

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...

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

Jay


shu2kill


Apr 26, 2010, 11:09 AM
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qtm wrote:
shu2kill wrote:
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....

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??


qtm


Apr 26, 2010, 11:14 AM
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shu2kill wrote:
qtm wrote:
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??

Put in some numbers and then worked backwards to figure out what would give the same result.


shu2kill


Apr 26, 2010, 11:15 AM
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Registered: Apr 8, 2008
Posts: 349

Re: [jt512] online force calculator [In reply to]
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jt512 wrote:
shu2kill wrote:
jt512 wrote:
shu2kill wrote:
qtm wrote:
shu2kill wrote:
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...

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.

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

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...

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

Jay

yes, i assumed it would be the same 30%. i do not know how to make it a variable depending on the fall factor. i believe the impact force would have something to do with the elongation, but i dont think its directly proportional, as the rope can only elongate so much....

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