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Thread: Physics and Fishing tips - breaking strain experiment

  1. #1 Physics and Fishing tips - breaking strain experiment 
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    Hi folks,

    I'm not in any stretch of the imagination 'a scientist', tho not to say I have interest obviously haha. I'm here tho with a possibly interesting question that will help me out as a slowly getting keener fisherman, and maybe a large percentage of the rest of the population too.

    I recently was donated some braided thread for sewing boat sails. It's got to be tough stuff.

    Intro: Fishing line is provided witha breaking strain in lbs on every spool for different situations and fish. The bigger the breaking strain the thicker the line (stands to reason haha), consequently you can fit less on a spool and it's more cumbersome and doesn't cast out half the distance of thinner line. Thus 'shock leaders' came to be, so that one can cast a long distance with thinner line but use a nice heavy weight. The principle of a thicker heavier small length of line attached to thinner stuff so that the small length of heavy line takes the strain of the weight being cast out at high velocity carrying the thinner more suitable line as far as possible. (for all those who don't fish, I hope you get the idea tho it's not really that important haha).

    Back to my sail sewing thread, I wondered if it would be perhaps a good shock leader but I need to find out its breaking strain.

    "How to do this simply with a bit of blue peter type cunning?"

    I had the idea I could construct a simple frame from wood, like a picture or door frame type affair which I could attach one end of the thread to the top of. Next I could attach a specific known weight to the bottom (increasing the weight gradually) and drop it a certain distance until the thread snapped.

    Sounds like it could work with all the kit I have here.

    I need to know from you beautifully clever scientist types what the maths or equasions would be (in joe blogs laman terms) for the distance of the drop, and weight used etc and how from all this I could work out the breaking strain of any given thread.

    I hope you catch my drift (sorry, pun, that was bad haha)

    Any help at all on the matter would be supremely fabulous.
    Cheers!


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  3. #2  
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    I wouldn't do it that way. Doing it as you describe, the string would break with a weight that is considerably less than the test weight of your string. How much less would depend on the stretchiness of the string. A stretchy string with more give would handle a larger weight than a stiff string would. I suppose you could do some more tests to determine how stretchy it is, but why bother?

    The easy way to do it would be to construct a windlass, then just slowly lift the weight. The weight that breaks the thread is the strength of the line.

    You will want to wrap the thread smoothly around the windlass, and the test weight, to make sure there are no pinch points to cut into the thread. Of course, being a fisherman, you know how to tie a knot that develops nearly the full strength of the line.

    The other way to do it if you have a spring scale or digital scale that has sufficient capacity, would be to anchor the thread solidly and slowly pull on it with the scale until it snaps. The reading on the scale just before it snaps will tell you the line strength.


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  4. #3 Re: Physics and Fishing tips - breaking strain experiment 
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    Quote Originally Posted by MrCat
    Hi folks,

    I'm not in any stretch of the imagination 'a scientist', tho not to say I have interest obviously haha. I'm here tho with a possibly interesting question that will help me out as a slowly getting keener fisherman, and maybe a large percentage of the rest of the population too.

    I recently was donated some braided thread for sewing boat sails. It's got to be tough stuff.

    Intro: Fishing line is provided witha breaking strain in lbs on every spool for different situations and fish. The bigger the breaking strain the thicker the line (stands to reason haha), consequently you can fit less on a spool and it's more cumbersome and doesn't cast out half the distance of thinner line. Thus 'shock leaders' came to be, so that one can cast a long distance with thinner line but use a nice heavy weight. The principle of a thicker heavier small length of line attached to thinner stuff so that the small length of heavy line takes the strain of the weight being cast out at high velocity carrying the thinner more suitable line as far as possible. (for all those who don't fish, I hope you get the idea tho it's not really that important haha).

    Back to my sail sewing thread, I wondered if it would be perhaps a good shock leader but I need to find out its breaking strain.

    "How to do this simply with a bit of blue peter type cunning?"

    I had the idea I could construct a simple frame from wood, like a picture or door frame type affair which I could attach one end of the thread to the top of. Next I could attach a specific known weight to the bottom (increasing the weight gradually) and drop it a certain distance until the thread snapped.

    Sounds like it could work with all the kit I have here.

    I need to know from you beautifully clever scientist types what the maths or equasions would be (in joe blogs laman terms) for the distance of the drop, and weight used etc and how from all this I could work out the breaking strain of any given thread.

    I hope you catch my drift (sorry, pun, that was bad haha)

    Any help at all on the matter would be supremely fabulous.
    Cheers!

    I truly do not know if pounds of test, are shock load, or just strain load. I used to make fishing equipment when I was a kid. I should know or should have known. Ha-ha.

    Usually when the line breaks, that is a minimum of 35 percent, beyond its work load whether it be a shock or strain load.

    One thing in my defense I never took those type of ratings to seriously. Because as fishing line gets old or when metal cable gets old, it weakens substantially. Also just using it weakens it. Chain holds its own well over time. As long as it does not rust. Chain does not bend and flex. Cable and fishing line does.

    And we all well know what happens to metal and plastic if you flex it. Even slightly.

    Sincerely,


    William McCormick
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  5. #4  
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    Ha, yes I did think later of the difference between the shock of a weigh dropping from totally slack to totally taught line v's the actual strain of the weight on an already taught line as it would be when casting...

    The windlass idea seems the best.

    Thanks for the replies!
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  6. #5 Tensile test continued 
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    Ok, I've looked up some more stuff. It has been suggested that knowing the weight of water and a bucket, simply attach a bucket to the bottom of the line and start adding water! Practical up to a point where you need more weight than is viable in that quantity of water.

    So I got out the bathroom scales to weigh some heavy stuff! I then wondered if putting something onto the scales and registering the weight before slowly lifting it off the scales with the line until it snapped and registering the lightest I was able to make the object would also give me the same result. Seems logical!

    But...

    I also found "All lines are classified by their breaking strain. This is the amount of pressure and not the dead weight that a fishing line will take before it snaps".

    Is there a way to figure out the pressure from a dead weight lift?
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  7. #6  
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    You could tie the thread to different fishing lines of known strength. Then just do a 'tug of war' to see which breaks first. Then switch the fishing line to a different strength accordingly until you have honed in on the approximate strength of the thread.


    Cheers
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  8. #7 Re: Tensile test continued 
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    Quote Originally Posted by MrCat
    But...

    I also found "All lines are classified by their breaking strain. This is the amount of pressure and not the dead weight that a fishing line will take before it snaps".

    Is there a way to figure out the pressure from a dead weight lift?
    I think the author of that was a bit confused. The breaking "strain" given in pounds or kilograms force, is not the same as the term "strain" used in materials science. As used in material science, strain is a measure of the deformation of materail caused by stress. Pounds is a unit of force, not pressure. If you are looking for a pressure, the proper material science term for that is "stress" and is given by the force divided by the cross-sectional area of the line.
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  9. #8  
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    Tug of war! cunning thought, I like it.

    I rigged up a couple of legths of the different lines I have and noted their printed breaking strains, then attached a bucket close to the ground and filled it with water and measured the quantity to snap-point for each.

    I only had four different known lines to test tho, and the results aren't as obvious as I'd hoped. The measuring wasn't super amazingly acurate, but near enough for the job.

    Annoyingly the 12 and 15lb lines took just about the same, approx 21oz to break.
    24lb line managed to take about 28.25oz, whereas the 30lb line took approx 39.25oz !
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  10. #9  
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    That doesn't seem right. Do you mean ounces or pounds?
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  11. #10  
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    Quote Originally Posted by Harold14370
    That doesn't seem right. Do you mean ounces or pounds?
    He could mean ounces. I know when I was a kid, we would cast our lines out and a couple times I got a snag on one of the fishing poles eyelets. It would break the fishing line. And you would watch your sinker or heavy lure just fly off.

    But you cannot put to much faith into plastic line. Or even metal cable. It is not an engineering standard as originally put forth and adhered to in engineering. Like chain still passes.

    Once they used it in manufacturing and for structures and elevators, and did not prove it was an engineering type structure, instead of admitting it. They just covered it up. Made standards and that was it.

    I was next to an older giant tow cable when it snapped. The tow truck was on ice, and slipping along on the ice. It suddenly just popped a heavy one inch steel cable.

    That is why I mentioned I never put to much trust in those measurements. You should not trust cable measurements either.

    Years ago in the Army as a blacksmith you learned not to trust cable. There were procedures when you used it to stand away from it. And to shield yourself from it.

    For all you know they might mean you can reel in a six pound fish with six pound test. But try it with a five pound eel, or a flat bottom fish in current.

    You could do it if you set the tension of the reel to slip at the six pound test break point. But otherwise you loose the fish.

    On the other hand, I have had a heck of a hard time, trying to break some of that heavier plastic line when it got tangled around something.

    It is great for putting across a walkway to alarm it, or Bobbie trap it. When someone walks into it, it pulls a piece of cardboard or plastic, out from between two metal contacts or two wires. To make a connection and set off an alarm or bomb.


    Sincerely,


    William McCormick
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  12. #11  
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    Ha, yes there was a mistake or two! Oh dear, well spotted.

    12 and 15lb line took 7.25 pints of water
    24lb - 13 pints
    30 - 21.75 pints

    (Measurements of just the water, so they need the bucket added; which is 1lb 12oz - unfortunately I made a sepereate note of a different container weighing only 12oz which I added on at the end in my haste. So it's infact off by 1lb each time)

    Ahh and mess up number 2, I measured a pint at 1lb 4oz, and then done the maths with pints x 1.25 (lb's) but wrote oz.

    (It was late haha)

    Tho the seemingly random difference in results for each line should still be there. Unless it's some kind of funny expinential calculation or whatever you call it, but I'm not legendary at maths I confess!

    Back to the drawing board.
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  13. #12  
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    My momma always told me "a pint's a pound the world around."
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    Oh no...this forum is fab but I feel so silly now. I'm sure it was my gcse's many years back the last time I did a practical experiment like this. Tho no excuse for such blatant sloppyness really haha.

    Yea I found an endless debate on the weight of water on a bulliten board somewhere, it could be I neglected to remove the weight of the glass I weighed it in afterward. Makes the maths easier tho :-D ...Oh I found tho that there are 20fluid oz in an imperial pint and 16 in US fluid oz.

    Sorry folks, think I'll start again.

    It turns ouy that the ex-pig farmer who works on the estate her has some scales for weighing pigs he doesn't need anymore, he may well remember to bring them in after lunch today as promised...hoorah, tho it does really defeat my aim of a proper blue peter househould tat and an empty fairy liquid bottle type test for any occasion.

    I do sometimes wish I'd taken in more from my science teachers, but like practically anything in life I suppose it only really stays well when one puts it to practical application often or has a particular need.
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  15. #14  
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    Quote Originally Posted by MrCat
    Oh no...this forum is fab but I feel so silly now.
    Would you want someone that asked you a question, or made an unintended error, to feel silly? I am going to take an educated guess here and say "Of course not". So why would you feel bad at all?

    If you cannot come here and feel great about having the balls to talk about stuff that is complex, if only in the vast array of conversions, opinions and registered trade mark, exclusive science and labeling practices. Then what is the sense of the forum?

    I loved the memories it brought back.

    But I do hate to error, when I do not mean to. I often get so into some piece of information that is so fascinating, that I forget the little things myself.


    Sincerely,


    William McCormick
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  16. #15  
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    Cheers matey, :-D

    Oh I love asking questions in places such as this, isn't the net brilliant (ish). Experts just ready to give you a pointer in their spare time. Just wish I was infallibale sometimes haha, don't we all.

    Reminds me of my fountain pen and copy book and relatively care free days.

    "Apperatus:
    Method:
    Results: ..."

    Conclusion: "Either do more tests or go see those nice people in the maths forum. Possibly both. Alternatively for some reason the logic of which totally and utterly escapes me, it might just be a bit random full stop with a test like this, tho you would have thought otherwise!"

    I've too little to go on so far I think. If I round things off to easy approximate figures I see that '12lb test' line takes approx 10lb more than its test rating to snap in this context. 24lb line takes approx 5lb over and yet 30lb line jumps back up to about 10lb over again.

    If someone markets 12lb line, it's 12lb the world around haha, quality and manufacturer in this case should only dictate perhaps the tiniest difference in thickness, but that obviously is minimal.
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