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Storing energy in fabrics

  1. Aug 21, 2003 #1

    I need a quick primer on what I think is spring elastic energy...

    Here is the argument: Idiots who want to discount how much aid in lifting heavy weights the atire that they are wearing is giving them are denying that the following type of suit gives them a great deal more help than a super strong single layer polyesther suit,. picture this, a wrestling singlet made from 2 layers of strong canvas fitted extremely tightly to the lifter especially in the hip area, etc. The lifter then squats down deeply loading spring elastic energy (?) into the suit, which then helps him return to the upright position with a far heavier weight than he could in just a pair of common shorts or a common singlet. Now, the real argument lies in that these guys are denying that a suit such as this double layer canvas thing does not add that much more to how much they can squat relative to the modern super polyesther single suits available which is ipso facto bull****. Could you help me with some explaanations concerning energy stored and streength of fabric, etc?

    It would be greatly appreciated.
  2. jcsd
  3. Aug 22, 2003 #2


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    Insignificant. The only enery that could be stored would be in the pants. Maybe if you had a spring-loaded knee brace it would help, but thats about it.
  4. Aug 24, 2003 #3
    well, I dunno, maybe if the guy's bending over.. wait, I was thinking his back would be curved, but then if you try to lift weights like that you'll just tear yourself apart

    I've never lifted serious weights.. the most I ever power-cleaned was like 100 pounds, since I never went to a real gym between now and the time I finished growing to full-size, and my buddy's barbell can't handle any more than that

    I wouldn't be too surprised if stretching some sort of double-layered canvas pants would store up some moderately impressive energy, though

    I mean, if the canvas on the front of the knees gets stretched by three inches, and there's a huge spring constant, it might give the guy an extra 20 pounds or so of force upward for a couple of seconds

    I can't find any info on the spring constant of canvas, or whether it stretches like a linear spring at all, unfortunately..

    Maybe you oughtta just head down to the gym with a change of pants and get some empirical data
  5. Aug 25, 2003 #4


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    The problem is torque. Your knee is maybe 3" in width front to back, so 1.5" from center for the lever arm. Your lower leg is about 12". So that means you need 8x the force on your knee as you get doing a leg extension with your ankle.

    A person in reasonable shape can lift 100 lb in a leg extension, 50 per leg. So the force generated on each knee would need to be 400 lb to cover that.

    So when I said you could use a spring-loaded knee-brace, we're talking springs you could use on a car's suspension.

    People often overlook it, but our muscles are actually capable of generating tremendous forces.
  6. Aug 25, 2003 #5

    I can get under a barbell loaded with 700 pounds on it, put the bar across my my shoulders and do a squat with it. In powerlifting we use suits- they are like wrestling singlets in apperance- THEY DO NOT GO WITHIN 3" OF THE KNEE! We use super tight strong knee wraps on the knees (mine add around 50 pounds). These suits take you and your helper up to 20 minutes to get on. They EXTREMELY TIGHT. They provide a great deal of support in the hips, in some of the double layer canvas suits when combined with "briefs" made of double layered super strong polyester take close to 900 pounds in the squat to push you down low enough for the lift to count. These suits can ad 200+ pounds to what you could squat without them!

    My argument was with some idiots who claim that a SINGLE layer super polyester suit can aid you as much as the double canvas- THAT'S BULL****! I wanted a physics explanation to explain how the suits aid you and why that the double canvas would aid you so much more!
  7. Aug 26, 2003 #6


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    Jeez, and thats allowed?

    Anyway, I had no idea you were talking about wrapping your lower torso and legs with 50lb of fabric. I doubt the fabric has a definable spring constant, but the effect is the same: it resists bending in your knee, taking some of the load off of your quads.
    Well, like I said before - the single layer would have to be extrodinarily strong - which would also make it extrordinarily tight.
  8. Aug 26, 2003 #7
    Hi Jay,
    Welcome to Physics Forums.

    Yeah, I think that we had no idea you were talking about that kind of weight. You have to remember that we're a bunch of nerdy geeks. Still, the ratio is the same as KillaMarcilla was talking about 20 lbs to 100 lbs is the same as 200lbs to 1000 lbs.

    Perhaps you are right about the fabric playing a role, however, the difference may be caused by the deformation of the muscles of the lifter, rather than the spring provided by the fabric. This is where the more lively "spring" action would be demonstrated. Still I agree that multi layers of canvas are going to give more support and enhance this effect.

    A test for the elasticity of the suit alone may be to suspend canvas and polyester suits from a beam, attach some weights to the suits and pull the weights down to see if either provides the force to return the weights to position or beyond. Just a thought, but be careful, this could be dangerous.
  9. Aug 26, 2003 #8
    Well now

    Go here:


    Watch the videos, think about the dynamics involved...

    Thanks for the help but I need more in concreto presentations of what is occuring...I graduated summa with a degree in Philosophy but am far from ignorant as per Newtonian (Classical) mechanics...I am just not completely certain as to how to mathemacally represent my argument.
  10. Aug 27, 2003 #9
    Re: Well now

    I use Netscape and I must be missing a plugin or something because I couldn't download the video.

    I did a little research and found what I suspected. That Canvas has a fairly high modulus of elasticity, however, when it is stretched and allowed to return to shape, at 50% return it deforms (over time) to 17% leaving it a soft pliable solid. This is not as true of human muscles which vary their shape to continue returning to position. So you may have some spring action, but after reaching 50% of the return to shape you lose most of that effect, except that the muscles of the lifter continue to change postion against the fabric.

    I'm not the guy to provide you with the mathmatical background for this, but I'm sure some of the others around here can.

    Good luck in your quest.
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