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  1. #11
    Senior Member StrungUpNewfoundlander's Avatar
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    The timing on this is amazing. I was just drawing out the Free Body Diagram to post it in response to an old thread but this is a much better job than I could do.

  2. #12
    Thank you for the very informative video! The physics at work in hammocking, and the mathematics used to model them are fascinating!

    I am about to go watch more of your videos, but had a question after watching this one...

    How does adding a structural ridge line change the vectors in play? You mention in the video at one point that it can have an impact on things. Curious to hear your thoughts!

    Thanks again,

    Cheers!!

  3. #13
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by LTMillar View Post
    This is fantastic!
    Link has been sent to my 10 year old (hopefully he will stop asking me those questions).
    Dave
    Cool! I'm sure a 10 year old will like crashing hammocks and cartoon rocket ships <grin>
    Quote Originally Posted by sidneyhornblower View Post
    This video is too cool for words. I bet tent campers don't know and discuss stuff like this. I feel elite.
    Thanks, I appreciate your appreciation. It's true the engineering (which is a fancy word for tinkering) aspect of hammocking drew me into it as a hobby, while the difference in rest I get in a hammock vs. on a lightweight ground pad keeps me in, the less flexible I get.
    Quote Originally Posted by Bubba View Post
    Nice to see a new video from you!
    Bubba! great to see you still here. Hope you got the shuttling back and forth across the US/Canada border thing sorted out. I remember you commenting on it a while back, sounded suboptimal.
    Quote Originally Posted by morgan1840 View Post
    Thank you for the video lesson Grizz. Very interesting and informative. I watched from my hammock and you were right, I fell asleep and slept like a baby.
    Yep, college professors droning on about mathematics has that well-known effect on people!
    Quote Originally Posted by Chesapeake View Post
    Excellent vid! I love the QED, lol.
    Glad you recognized the reference! Admittedly a bit of insider baseball, but I couldn't help myself. For those that don't know, two thousand years ago greeks like Euclid and Archimedes (of 'Eureka! I have found it' fame) used a phrase was translated into Latin as, Quod Erat Demonstrandum, and used as such beginning in the Rennaissance. In the greek what was said was 'The very thing it was required to have shown'. Used in math to indicate that the text of a mathematical proof is completed.
    Quote Originally Posted by StrungUpNewfoundlander View Post
    The timing on this is amazing. I was just drawing out the Free Body Diagram to post it in response to an old thread but this is a much better job than I could do.
    Great, always happy to save someone effort. Though I rather suspect your explanation would be more terse...
    Quote Originally Posted by moogin View Post
    Thank you for the very informative video! The physics at work in hammocking, and the mathematics used to model them are fascinating!
    I am about to go watch more of your videos, but had a question after watching this one...
    How does adding a structural ridge line change the vectors in play? You mention in the video at one point that it can have an impact on things. Curious to hear your thoughts!

    Cheers!!
    great, thanks for watching. I had intended to work in more explicit discussion about the structural ridgeline, and for that matter, sheer force on the tree, but that will have to wait for the sequel.

    So, what I've presented here works when a structural ridgeline is present. If you look closely at the cartoon Grizz in a hammock at the beginning, there is ridgeline present, and the angle of the cord from the corner to the tree is a little shallower than the angle of the hammock body as it approaches the corner where the ridgeline attaches. Indeed the same approach describes the stress on the hammock body as a function of that angle, which will be less than the stress on the cord because the angle is deeper (it is a little more complicated because of the pull of the ridgeline though .... there is another force on the corner of the hammock pulling in, but the take-away message is the same.)

    Using a structural ridgeline necessarily creates a shallower hang angle on the cord than on the hammock. What you want to do is tighten the suspension to the point that there is just enough tension on the ridgeline when you are laying out flat so that it is straight and under tension. Any more than that is just introducing forces into the system that are unnecessary. The ridgeline is there to keep the hammock ends at a fixed distance, and once the suspension is tight enough to do that you don't need it any tighter.
    Last edited by GrizzlyAdams; 07-03-2018 at 18:59.
    Grizz
    (alias ProfessorHammock on youtube)

  4. #14
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    Quote Originally Posted by GrizzlyAdams View Post
    ...

    So, what I've presented here works when a structural ridgeline is present. If you look closely at the cartoon Grizz in a hammock at the beginning, there is ridgeline present, and the angle of the cord from the corner to the tree is a little shallower than the the angle of the hammock body as it approaches the corner where the ridgeline attaches. Indeed the same math describes the stress on the hammock body as a function of that angle, which will be less than the stress on the cord because the angle is deeper.

    Using a structural ridgeline necessarily creates a shallower hang angle on the cord than on the hammock. What you want to do is tighten the suspension to the point that there is just enough tension on the ridgeline when you are laying out flat so that it is straight and under tension. Any more than that is just introducing forces into the system that are unnecessary. The ridgeline is there to keep the hammock ends at a fixed distance, and once the suspension is tight enough to do that you don't need it any tighter.

    I'd phrase it as "just barely taut", essentially with the least possible tension. I see the SRL as serving two purposes. First, it holds up the bug net! As "important" as that is, what it mostly does, IMHO, is serves as a measure for getting the hang angle correct. The difference in hang angle between the cord and the hammock should be so slight that it is essentially imperceptible.

    Grizz is spot on in saying that having it any tighter introduces unnecessary forces into the system. At any significantly shallower hang angle the SRL ends up taking on a large proportion of the force and may even snap. If it's only a little bit too tight, it will serve to maintain the proper sag in the hammock. But better to have it just right in the first place.

    Great vid! The contributions that folks like you make are simply incredible.

  5. #15
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    Once upon a time, I wrote "QED" at the bottom of a proof for a first-year Engineering Physics problem set. I received it back with a 10/10 grade at the top and, in the same red ink, the comment "QED is generally reserved for the longer proofs" at the bottom. It was 10-pages, handwritten (and I have small handwriting). I've never used it since.

    Thanks for your vid. It was fun. For added nerdiness, I measured and calculated my pistol angle: 31.8°

  6. #16
    Senior Member TrailSlug's Avatar
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    Oh wow. Now I'll never fall asleep in my hammock again thinking about all of this math.

  7. #17
    Herder of Cats OutandBack's Avatar
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    It is so good to see the Professor back in front of the camera.

  8. #18
    Recalc's Avatar
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    Quote Originally Posted by framjam View Post
    Once upon a time, I wrote "QED" at the bottom of a proof for a first-year Engineering Physics problem set. I received it back with a 10/10 grade at the top and, in the same red ink, the comment "QED is generally reserved for the longer proofs" at the bottom. It was 10-pages, handwritten (and I have small handwriting). I've never used it since.
    I thought QED is to the mathematician as "ta da" is to the magician.

  9. #19
    Senior Member WV's Avatar
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    Quote Originally Posted by GrizzlyAdams View Post
    Any more than that is just introducing forces into the system that are unnecessary. The ridgeline is there to keep the hammock ends at a fixed distance, and once the suspension is tight enough to do that you don't need it any tighter.
    Consider the larger system that involves varying tree-to-tree distances, landforms, and people of different heights. Tolerating additional forces on the main suspension lines and the structural ridge line may be the key to having my hammock the right height above the ground. If the trees are far apart, and I can't reach high enough to place my tree straps, the structural ridgeline is a necessity (sine qua non). If the trees are the perfect distance apart, it's nice, but it's just a convenience.

  10. #20
    Senior Member GrizzlyAdams's Avatar
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    Quote Originally Posted by TominMN View Post
    Great vid! The contributions that folks like you make are simply incredible.
    Appreciate that. In my day job we are concerned about "impact", how what we teach or research influences others. So it's natural for those of us in the education biz to share...and I at least like the whole process of conceiving and implementing a video. The shooting of it not so much.
    Quote Originally Posted by framjam View Post
    Thanks for your vid. It was fun. For added nerdiness, I measured and calculated my pistol angle: 31.8°
    These days it is more typical to put a filled in square to mark the end of the proof.You win the neediness prize with your finger measurement.
    Quote Originally Posted by TrailSlug View Post
    Oh wow. Now I'll never fall asleep in my hammock again thinking about all of this math.
    Sorry about that. Try hiking 25 miles first with a full pack. That will help!
    Quote Originally Posted by OutandBack View Post
    It is so good to see the Professor back in front of the camera.
    And me with a face for radio ... Glad you like 'em when I can get them out.
    Quote Originally Posted by Recalc View Post
    I thought QED is to the mathematician as "ta da" is to the magician.
    I like that!
    Quote Originally Posted by WV View Post
    Consider the larger system that involves varying tree-to-tree distances, landforms, and people of different heights. Tolerating additional forces on the main suspension lines and the structural ridge line may be the key to having my hammock the right height above the ground. If the trees are far apart, and I can't reach high enough to place my tree straps, the structural ridgeline is a necessity (sine qua non). If the trees are the perfect distance apart, it's nice, but it's just a convenience.
    Fair enough. You just need to be sure the cord and webbing you're using are up to snuff, knowing that 1/sine(theta) gets pretty big pretty fast as theta diminished less ithan 15 degrees. Almost 6 when theta = 10 degrees. I would restate the rule that you shouldn't put any more force in your system than you need to in order to achieve your desired hang.
    Grizz
    (alias ProfessorHammock on youtube)

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