# Catapult Bands Demystified: It's Physics!



## phoghat

*It's all in the physics:*

Have you ever wondered what type of band would give you the best accceleration (therefore the greatest speed and power) ? Well, with the use of physics, and some high speed cameras, you can find out. No guesswork, old wives tales, or "seat of the pants" guesswork involved. Joerg Sprave, over on the Slingshot Channel on You Tube has eliminated any guesswork involved. All he needed was a slingshot, some different types of bands, and about a Gazillion dollars worth of equipment.






As you can plainly see, a tapered band will give much better acceleration, therefore much more power, than an untapered band. Better living through Science.


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## ZDP-189

phoghat said:


> *It's all in the physics:*
> Have you ever wondered what type of band would give you the best accceleration (therefore the greatest speed and power) ?


Thank you for posting this. Yes, recently I have wondered about it pretty much constantly 24/7 in a fairly intense sort of way.

Jörg and I have been collaborating on uncovering the science behind bands. My blog entry that Jörg references in his video and links in his notes to the video is published here on this forum.

http://slingshotforum.com/blog/11/entry-408-tapered-flatbands-mechanism-and-effect/

It's a little more 'deep' than he goes into on his video, but it is from the same data set and Jörg says he agrees with my analysis and findings. If you really want to go into detail, examine the math and physics behind my calculations and aren't shy about getting into greek symbols and second derivatives and MS Excel formulae, then I also have spreadsheet I can let you download. PM me and I'll give you a link.


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## Dayhiker

Science will always take over where "seat of the pants" has learned all it can. And it will bring things to higher levels of efficiency. That's why I'm glad there are scientists and engineers around. Kudos to Joerg, Dan, and whoever else does this stuff.


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## harpersgrace

_Thanks but no thanks,I can appreciate the work that has gone into all this "study" of the lowly slingshot and I'm sure that others will find it very interesting but the seat of the pants is fine by me._


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## M.J

Those videos were pretty awesome!
I'm still going to be shooting 107s and Chinese tubes.


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## AZshooter

Very impressive studies, and nobody with sense could dispute all these studies...Practical shooting demands something more substantial { in cost and longivity }, than short lived super-fast bands...In cold weather so;ids still stand best, and the function and long life of tubes and gum rubber can`t be ignored by practical everyday shooters...impressive but not practical


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## ZDP-189

harpersgrace said:


> _Thanks but no thanks,I can appreciate the work that has gone into all this "study" of the lowly slingshot and I'm sure that others will find it very interesting but the seat of the pants is fine by me._


In a way, I agree. We all like slingshots, but everyone likes them in a slightly different way. I like it primarily as an intellectual pursuit and you like it as a pure sport. They are both flip sides of the same coin. I hope you will allow me to explore this topic fully and maybe any new knowledge will result in better bands that you can enjoy.

Likewise, there is nothing at all wrong with shooting square solids on a classic milbro or natural fork. Or tubes for that matter. Anyone who tells you that there is only one right way is wrong. Anyone who tells you that one way is better may only be correct in certain circumstances.


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## Charles

I saw this video yesterday, and I did enjoy it. However, I must say that I do not see how it advanced our understanding of the phenomenon. We all (or at least most of us) know that tapered bands are faster. That very high speed video was graphic confirmation of something we already know. It certainly was neat to see it all in slow motion. But it did not in any way explain what we already knew.

Several of us on the forum have come to the conclusion that the increased speed of tapered bands is the result of two factors:

1. The more tapered part of the band gets stretched closer to its elastic limit, which means it recoils faster.

2. The mass toward the pouch is reduced; since the pouch end of the band has to be accelerated over the longest distance, the smaller the mass there, the faster the over-all retraction.

I saw nothing in the video that contradicted these conclusions, nor that confirmed these conclusions. The sort of analysis already done and proposed by ZDP-189 is, by contrast, an attempt to understand the physics of the phenomenon.

Again, just to be clear: I liked the video. I found it very interesting. It is easily the best of that sort I have seen. I do not fault the video in any way. BUT the video certainly does not constitute a piece of science. It revealed in very slow motion the phenomenon of interest: tapered bands are faster than straight bands. It did not explain why that is so.

Cheers ...... Charles


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## pop shot

Charles said:


> I saw this video yesterday, and I did enjoy it. However, I must say that I do not see how it advanced our understanding of the phenomenon. We all (or at least most of us) know that tapered bands are faster. That very high speed video was graphic confirmation of something we already know. It certainly was neat to see it all in slow motion. But it did not in any way explain what we already knew.
> 
> Several of us on the forum have come to the conclusion that the increased speed of tapered bands is the result of two factors:
> 
> 1. The more tapered part of the band gets stretched closer to its elastic limit, which means it recoils faster.
> 
> 2. The mass toward the pouch is reduced; since the pouch end of the band has to be accelerated over the longest distance, the smaller the mass there, the faster the over-all retraction.
> 
> I saw nothing in the video that contradicted these conclusions, nor that confirmed these conclusions. The sort of analysis already done and proposed by ZDP-189 is, by contrast, an attempt to understand the physics of the phenomenon.
> 
> Again, just to be clear: I liked the video. I found it very interesting. It is easily the best of that sort I have seen. I do not fault the video in any way. BUT the video certainly does not constitute a piece of science. It revealed in very slow motion the phenomenon of interest: tapered bands are faster than straight bands. It did not explain why that is so.
> 
> Cheers ...... Charles


I'm with charles. Master of the obvious. this should be titled "Tapered bands are faster vs. 'look, tapered bands are faster'."


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## Dayhiker

Well, if I were a newcomer to this, the demonstration would make things clear. Sometimes it is difficult to really be objective about what you're shooting without some kind of an experiment.

Case in point: all the folks who think thick tubes are more powerful. Then the chrony and a little math (science) tells the tale.


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## Nico

Charles said:


> I saw this video yesterday, and I did enjoy it. However, I must say that I do not see how it advanced our understanding of the phenomenon. We all (or at least most of us) know that tapered bands are faster. That very high speed video was graphic confirmation of something we already know. It certainly was neat to see it all in slow motion. But it did not in any way explain what we already knew.
> 
> Several of us on the forum have come to the conclusion that the increased speed of tapered bands is the result of two factors:
> 
> 1. The more tapered part of the band gets stretched closer to its elastic limit, which means it recoils faster.
> 
> 2. The mass toward the pouch is reduced; since the pouch end of the band has to be accelerated over the longest distance, the smaller the mass there, the faster the over-all retraction.
> 
> I saw nothing in the video that contradicted these conclusions, nor that confirmed these conclusions. The sort of analysis already done and proposed by ZDP-189 is, by contrast, an attempt to understand the physics of the phenomenon.
> 
> Again, just to be clear: I liked the video. I found it very interesting. It is easily the best of that sort I have seen. I do not fault the video in any way. BUT the video certainly does not constitute a piece of science. It revealed in very slow motion the phenomenon of interest: tapered bands are faster than straight bands. It did not explain why that is so.
> 
> Cheers ...... Charles










I couldn't say it better.. I had to edit this, I forgot to add.. That for those who put down personal experience stating that science is better? Are greatly narrow minded folks for it is through experience that any scientific experiment is even possible.. For that matter this is at best pseudo science and has not evolved anything that is not already known.


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## Deltaboy1984

Interesting study using math I have not delt with since my College physics days.


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## Charles

I want everyone to understand my comments. I Really liked the video. I mean no disrespect to Joerg or any of the folks involved in the making of the video. I agree with DH that it is very helpful for newcomers (and oldies too) to see those tapered bands in action and be able to compare them in slow motion to the straight bands. No fault on the video ... no fault anywhere. I just think there is a lot more that needs to be done to obtain a scientific understanding of our experience with tapered bands.

Cheers ...... Charles


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## Imperial

all this scientific stuff just goes over my head. i just go by instinct and what has worked for me in the past. im just a hobbyist, so that may be why.







 too geeky for me but i know a lot like this stuff. besides my common sense tell me that taper allows for more stretch than a sqaure flat cut, which pulls in the middle and not the edges whereas a taper allows for the whole band to stretch evenly. reducing resistance . thats as geeky i get.


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## Dayhiker

I don't even have to know this stuff. My brain is too small to understand it anyways. I don't know anything about the automotive engineering either, but when I'm considering buying a car, I'm thankful for the tests done by Motor Trend and others who do know. That's all I'm saying.

Well, maybe a little more. . .

Nobody ever told me I could kill a rabbit at close range by throwing a rock at his head real hard. I could figure that out for myself. Then you could get a bunch of rubber bands and put them on a slingshot and do the same thing wasn't much of a stretch to understand either. Where the real thinking comes in is matching ammo to bands. It amounts to this. You can kill a rabbit by throwing a rock at its head, but not so big a rock that it's too heavy to get any pepper on it, nor not so small a rock that it is a mere pebble. Now that you have your jumble of rubber bands, just apply that same principle. End of story. Anything else is pseudo science and narrow minded.

Heck if that was all there was to this hobby of ours, I'd have turned away in boredom in about 5 minutes.


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## marcus sr

Nico said:


> I saw this video yesterday, and I did enjoy it. However, I must say that I do not see how it advanced our understanding of the phenomenon. We all (or at least most of us) know that tapered bands are faster. That very high speed video was graphic confirmation of something we already know. It certainly was neat to see it all in slow motion. But it did not in any way explain what we already knew.
> 
> Several of us on the forum have come to the conclusion that the increased speed of tapered bands is the result of two factors:
> 
> 1. The more tapered part of the band gets stretched closer to its elastic limit, which means it recoils faster.
> 
> 2. The mass toward the pouch is reduced; since the pouch end of the band has to be accelerated over the longest distance, the smaller the mass there, the faster the over-all retraction.
> 
> I saw nothing in the video that contradicted these conclusions, nor that confirmed these conclusions. The sort of analysis already done and proposed by ZDP-189 is, by contrast, an attempt to understand the physics of the phenomenon.
> 
> Again, just to be clear: I liked the video. I found it very interesting. It is easily the best of that sort I have seen. I do not fault the video in any way. BUT the video certainly does not constitute a piece of science. It revealed in very slow motion the phenomenon of interest: tapered bands are faster than straight bands. It did not explain why that is so.
> 
> Cheers ...... Charles










I couldn't say it better.. I had to edit this, I forgot to add.. That for those who put down personal experience stating that science is better? Are greatly narrow minded folks for it is through experience that any scientific experiment is even possible.. For that matter this is at best pseudo science and has not evolved anything that is not already known.
[/quote]It pains me,but this dude has hit the nail clean on the head.My personal opinion is that this sorta experiment,trial call it what you will,while explaining one aspect of bands ie velocity etc etc in no way betters the experience of getting out there and trying it,finding what works for you.How long before this leads to the my bands are better than yours arguments allready prevellent all over place?Some say this will be of benefit to the beginner?how so?Just brings to mind the old saying "Baffled by ****" if im honest,Shouldnt we be saying to a beginner,heres a fork heres some rubber,heres some leather,crack on,get them doing it instead of sitting on there asses trying to decide which way to turn? I myself have just found the benefit of tubes again,goes against the majority for sure,but ive been there with flats,straight cut,tapered or otherwise,and it was done off my own back,the same as others have done,Nico has done it with chains,Harper with 1745 etc.no,i think ill just stick to my cave man ways and enjoy finding out what works for me the old fasioned way,trial and error.


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## ZDP-189

The word 'pseudoscience' has been used twice in this thread. To be precise, Wikipedia states:



> Pseudoscience is a claim, belief, or practice which is presented as scientific, but which does not adhere to a valid scientific method, lacks supporting evidence or plausibility, cannot be reliably tested, or otherwise lacks scientific status. Pseudoscience is often characterized by the use of vague, exaggerated or unprovable claims, an over-reliance on confirmation rather than rigorous attempts at refutation, a lack of openness to evaluation by other experts, and a general absence of systematic processes to rationally develop theories


While I'd agree this does apply to a lot of what is being written about slingshot hunting and a fair chunk of what is written about slingshot bands, please appreciate that what Jörg was doing is an attempt to depart from that.

I would love to simply pull up a published scientific paper that would deliver all the answers, but I can find almost no scientific studies on elastomers behaving in a manner analogous to slingshot bands, that is to say, pulling it back as far as it will go and releasing it. All the studies that involve high elongations are static stress-strain tests and most of them are under elongation, not contraction. All the dynamic studies involve oscillations at low elongations. There aren't any studies involving external inertial load. I can't even find an ASTM standard test for any of these, let alone one that combines them all. Most people are focused on synthetic rubbers, especially thermoplastic polymer elastomers (TPEs) and occasionally two-part thermoset elastomers. These are more relevant to commercial parts. The main application of natural rubber is tyres and belts because natural rubber dissipates heat better. However these use carbon black and other fillers to counter the other shortfalls of natural rubber: to increase hardness, modulus (make it less stretchy), strength (ultimate rupture strength) and surface abrasion resistance, none of which are priorities of slingshot bands. That's why you don't see many black slingshot bands.

Anyway, what this all means is we are SOL when it comes to finding research we can use in our pursuit of the better band. Not totally out of luck maybe, but it means we have to go to first principles, build our own theoretical models and gather our own data. What we can use from the literature is basic formulae for tension under stress and kinetics. We can also employ engineering methods such as calculus and finite element analysis to find optima and predict performance.

I fully appreciate that words like 'calculus' are a major turn off for most of us. We do this sport because of the pure fun of flinging things. That is why I bury my more cerebral writing in the blog, but I do try to be as rigorous and scientific as possible and putting it out there for the curious to find and contribute to or refute serves as a form of peer review.

At the end of the day, as long as somebody's looking for the answers and is willing to share the fruits of their pursuit, we can all benefit.


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## ZDP-189

marcus sr said:


> How long before this leads to the my bands are better than yours arguments










If there's anything I've learned about bands, it's that one shouldn't over generalise about what's best, especially without being very specific about the definition of fitness and specifying all the constraints.

All the debates about tubes vs flats vs chains vs solids and pure latex vs Thera-band vs Linatex vs synthetics are flawed because people have different requirements and test using different parameters. For example, I'd bet that the advantage of tapers versus straights would all but evaporate if the projectile was heavy enough compared to the draw strength and the draw of both bands was the same. Anyway, in most situations, any disadvantage can be made up with a bit more muscle, a longer draw or a different projectile. You'd have to pick something bizarre like five year old underpants' waistbands to come up with a universal loser. You really have to know how these bands work in different situations to know which has an edge for a certain situation and that's what the research trying to do.


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## NightKnight

ZDP-189 said:


> At the end of the day, as long as somebody's looking for the answers and is willing to share the fruits of their pursuit, we can all benefit.


ZDP...I, for one, really appreciate what you are doing. Where would mankind be if no one ever tried to study the behavior of materials and figure out how we can improve ourselves or our activities using them. Chances are, we would still be throwing rocks at rabbits heads. I love this stuff because I am admittedly a geek, but a geek who doesn't have much time (work, family, and faith) to do the testing that you so generously perform. I am positive that the sport will benefit from what you are doing, just as the sport benefited from the testing that Tex did with latex and tapering in years past. I am _*shocked*_ that people would post negative comments about this testing, as there is no way it can hurt anything to gather the information. I am pretty sure that had I lived in the 19th century I would not have been the guy that developed the internal combustion engine, but I still really appreciate that Nikolaus Otto spent many hours testing, iterating, and innovating for us. I am sure that he had neighbors and friends that said that steam engines, or horses, were good enough for getting around. If he had listened to them, where would we be as a race?


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## NightKnight

ZDP-189 said:


> You really have to know how these bands work in different situations to know which has an edge for a certain situation and that's what the research trying to do.


That is the beauty of everything. There is no one best solution for a given field. Continuing the vehicle analogy, sports cars are very fast on the road but are terrible off-road, while off-road trucks are good in mud and rocks, but cannot make it around a turn at higher speeds. Tires that are exceptional in the dry are terrible in the wet. For excellence in certain areas, there has to be compromises in others. This is an almost universal constant, but one that mankind always struggles with.


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## ZDP-189

Yes, let's not forget Bill's testing. The sport owes much of what it is today to his efforts.


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## Charles

ZDP, I am all in favor of your work. And as we have corresponded, I hope to be able to contribute a bit to it. I think it would be great to have a better understanding of the physics of slingshot bands. I confess to being rather geeky myself, having a number of graduate degrees in various sciences including physics.

And I really love Joerg's video. It is so cool to see what goes on in such slow motion.

My very mild negative comments were directed only to the view that the video itself constitutes a physical explanation of the fact that tapers are faster than straights. The video merely illustrates something we already know; the video does not explain it.

I for one am all in favor of more research into the topic of slingshots and slingshot bands. I do NOT see how it can hurt our sport to have available a better physical understanding of what is going on, for the use of those who are interested. There are those who are interested in the physics of archery; there are those who are interested in the physics of firearms; but the vast majority of folks in those shooting sports are not interested in the science behind what they are doing ... they just get out there and shoot ... and that is just fine. I think the same applies to slingshots.

Cheers ..... Charles


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## pop shot

I find the bowed out parachute effect of the bands themselves really interesting, also the full length/uniform rippling of the bands at the end of the power stroke.


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## monoaminooxidase

regarding the "how much science do we need?"-thing: all in all, I do not expect anything good to come out of a discussion conducted in this way, so I stopped following that after the fifth post.
I for one am curious why the tapered band are more effective. my first guess was it's just because the thin end of the band is stretched more and a thinner, shorter band might have a similar effect, but the longer I think about that, the less sense it makes. Did someone do a check test on that?
I have another question though: why does a rubber band heat up while it is stretched? I do not know nearly enough physics to come up with an explanation.
good night!


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## Tex-Shooter

Everyone that knows me knows that I got into the slingshot sport using facts learned through physics. Now having said that facts on paper are different than facts in the field because of variables. Different rubber compounds do strange things when subjected to different temperatures, humidity and other variables. I like to discuss the physics, but the real sport for me is when shooting. -- Tex


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## ZDP-189

pop shot said:


> I have another question though: why does a rubber band heat up while it is stretched? I do not know nearly enough physics to come up with an explanation.
> good night!


I don't want to get into thermodynamics, the Gibbs function, or free enthalpy in this particular thread, but suffice it to say that when you pull bands, you do work; i.e. you put energy into the bands. When you release the bands, they release energy and get colder. I'll do a blog entry on elastomer thermodynamics sometime.


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## monoaminooxidase

ZDP-189 said:


> I don't want to get into thermodynamics, the Gibbs function, or free enthalpy in this particular thread, but suffice it to say that when you pull bands, you do work; i.e. you put energy into the bands. When you release the bands, they release energy and get colder. I'll do a blog entry on elastomer thermodynamics sometime.


Well the "you put in kinetic energy which is transformed into heat"-explanation I've read before, but I was wondering if this was about friction within the material or something else. I'll try and google what you mentioned, I hope I'll understand half of it. Anyway, thanks.


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## ZDP-189

monoaminooxidase said:


> I don't want to get into thermodynamics, the Gibbs function, or free enthalpy in this particular thread, but suffice it to say that when you pull bands, you do work; i.e. you put energy into the bands. When you release the bands, they release energy and get colder. I'll do a blog entry on elastomer thermodynamics sometime.


Well the "you put in kinetic energy which is transformed into heat"-explanation I've read before, but I was wondering if this was about friction within the material or something else. I'll try and google what you mentioned, I hope I'll understand half of it. Anyway, thanks.
[/quote]

It's not due to friction. If it were indeed a friction process, the rubber would never rebound.

First, please just take my word for it that energy can't be created or destroyed. It can only be moved from one thing to another and one state to another. This is known as the First Law of Thermodynamics.

Rubber is comprised of many long chain molecules, all curled up. This is the natural shape of the molecules, a bit like tangled up springs. When the shooter stretches the rubber band he is drawing it out. The band doesn't gain or lose volume or matter, but work is done to bend and stretch the molecules out of shape, lengthening the molecules by straightening them. The increased internal energy can be felt as heat. If you heat the bands up, it would take more force to stretch the bands. When the rubber band is released, that energy is dissipated as useful work and the band cools down. This process of returning internal energy by snapping back to the original form is known as resilience.

It's not quite a perfect closed system. Some of that internal energy is lost, dissipated as heat and sound. The difference is known as damping, or hysteresis. Hysteresis is the energy lost between the stretch that is not recovered as snap. Measuring hysteresis (or resilience) under similar conditions of high amplitude dynamic stress is a good measure of how good a rubber band will shoot.

If you want to know a little more about hysteresis, I wrote an article about 18 months ago when i first got into the science of bands. My understanding has improved a lot since then, but it's worth a read:

http://slingshotforu...ng-your-energy/

But we've now digressed so far off topic and are using language so alien to most readers that we may as well be discussing the current price of lettuce in Chinese. If you have any more questions about the thermodynamics of rubber, please PM me. And if you want to discuss monoamine oxidase, I can do that too. I happen to have a degree in Pharmacology.


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## Nico

> But we've now digressed so far off topic and are using language so alien to most readers that we may as well be discussing the current price of lettuce in Chinese. If you have any more questions about the thermodynamics of rubber, please PM me. And if you want to discuss monoamine oxidase, I can do that too. I happen to have a degree in Pharmacology.


You should never make assumptions of the intellect or mental capaciy of the people who read on the forum.

You don't know who or what people's intellectual capacities are to say otherwise if basic English terms are alien to others or not.

I don't flaunt my educational background, everything you say is nothing new; I well understand the concepts of energy and I have my own understanding of physics. I hate math but I know how to use it, I am more practical in my approach to the world.

I too understand Pharmacology and I do have a scientific background, among other things I do not flaunt what I have.

I respect all who are here equally as we can learn something from everyone on here..

Nico


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## orion25

Bonjour,
Je suis nouveau sur le forum et je vous propose de trouver vous-même la réponse à votre question sur les bandes coniques. Avoir l'expérience suivante :
prenez une bande conique, tracez un repère à 1 cm pour fixer la bande puis des repères tous les 2 cm, sur un support de votre choix, fixez le bas de la bande avec une pince rapportée par exemple. rallonger le ruban d'un facteur 6, mesurer la position de chaque marque.
le premier repère est le point 0, le dernier sera utilisé pour le calcul de l'allongement réel.
1) Mesurez la longueur de chaque section.
2) Calcul de l'allongement de chaque section.
3) Calcul de l'allongement réel de la bande.
Quelles sont les conclusions ???
Nous pouvons comparer nos résultats si vous le souhaitez.
Bonne expérience et à bientôt j'espère.
Note : Désolé pour mon anglais mais j'utilise le traducteur google.


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## orion25

Hello,
I am new on the forum and I suggest you find yourself the answer to your question on conical bands. Have the following experience:
take a conical strip, draw a mark at 1 cm for fixing the strip then markers every 2 cm, on a support of your choice, fix the bottom of the strip with an attached clamp for example. extend the tape by a factor of 6, measure the position of each mark.
the first reference mark is point 0, the last will be used for the calculation of the real elongation.
1) Measure the length of each section.
2) Calculation of the elongation of each section.
3) Calculation of the real elongation of the strip.
What are the conclusions ???
We can compare our results if you want.
Good experience and see you soon I hope.
Note: Sorry for my English but I use the google translator.


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