Energy - Springs

[@kayeadolfo6451]

Thank you very much, I like how you teach.

[@mohfa1806]

Talented teacher who have the gift to deliver education in simple yet profound technique... Respect to you Prof. Anderson from lebanon

[@MrEloquentsilence]

Thanks Dr. Anderson. What happens if there is a block with mass 2m already on the spring? Basically box with mass M and velocity v hits a spring with a box already connected to a spring. How to differentiate between v before and v after contact and where to plug in total mass?

[@dennisgarber]

This assumes that you did not exceed the limit of the spring and permanently deform it. I am trying to create a 0 to 2ish meter shock absorber for a rope that can safely absorb the force of a 100 lb to 300 lb person falling up to 2 meters before the rope saves them from a 14 to 44 foot fall. (5600 lb is the official force of a 220 person falling 2 meters). A single stich of nylon sewn into a 900 lb tensile strength webbing weakened the webbing more than half. So, webbing is out. It looked like three half inch bungees cushioned 40 lb, OK. But 16 bungees per 1 or 2 meter loop cache, shock absorber in the top of climbing rope, got pricey for the needed 20 ropes. Plus, I do not trust elastic after 2 years. 4 meters of 1000 lb bungie folded in half, with 400 lb break aways every inch or two, works in scale on a 40 lb water bucket. This brings me to my 550 lbporch swing testing. I calculate 980 lb force, at least (assuming osha 3.2 inch system absorption and not less), dropping a 40 lb bucket 2 meters onto the rope. The 8.5 Inch porch swing seemed to absorb the force, but it permanently deformed 6 inches. I repeated the test 4 times, each time it deformed 6 inches... I am wondering if it could absorb 20 Kn, but I have no way of testing.

[@yoprofmatt]

Good stuff. Short answer is I have no idea the best way to do this. Obviously a beefier spring would do it, but this seems clunky. I think you mentioned the energy absorbing harness (like this one: gravitec.com/energy-absorbers/) with the stitched webbing. This was new to me, but pretty cool. Anyway, I wish you the best of luck. Seems challenging. Cheers, Dr. A

[@dennisgarber]

@@yoprofmatt I have completed the scale tests and have a design for making my own breakaway shock absorber. After much trial and error, I settled on 5600 lb 2" seat belt webbing and 138 bonded thread. Two inch zig zag measured 320 lb to break. By doing it myself, I can envision using 20 units easily. And, I can do 3 stages of resistance so that the first stage doesn't hurt a thin boned 100 lb person, also more half harness friendly. But the design will also safely stop the 350 lb guy, or the 4 meter fall. The physics math to predict the number of break aways (initial lbf when hitting the first break away + the force gained during the stop distance). The math to calculate the number of breakaways is about 15 to 30 percent off for my 40 lb dropped 2.4 meters and 1 breakaway force per inch, 9 inches to stop. (I calculated the 9 inches, at the initial velocity, as non trivial.) Might be worth a video. I have spent weeks on this and can answer any questions. Furthermore, I also bought 10 Kong Kisa shock absorbers. Look them up. I will eventually get around to posting a few clips. The Kisa relies on static and kinetic rope friction. What I learned in my testing is that the company cannot predict the friction of anyone's rope. There are so many factors : rope mantel creep, mantel brand friction, turn radius, dampness, wetness. My cheap 10.5 mm rope would have put a 220 guy under 1500 lb of force in a 2 meter fall with a dry rope. As soon as my rope got wet the slide,, stopping distance decreased dramatically, in addition to short stopping distance. With the Kong Kisa, everyone has to decide for themselves what they feel is safe. The numbers they give for threading are suggestive and not likely to represent your rope..... So, in the end, I settled on a target of 9 inches slide, 1200 lbf (40 lb dropped 2.4 meters) , on my dry 10.5 mm rope. Wet the slide was 5 inches. I think it will be enough with 2 meters of feed rope.... Of course, I don't know how much the static or kinetic friction are with the kiss. I mounted a winch on the swing set with a 600 lb crane scale opposing. Unfortunately, the most I was ever able to crank on the winch was 300 to 350. Going past 250 lb was difficult. I was not able to to pull the kisa on the winch even at a lower hole weave than the instructions mentioned.. The kisa stopped bucket looked a bit more violent than the break away webbing, plus it can't be progressively staged to handle 100 to 400 lb people like the webbing. Of course, if I were smart enough, I would figure out how to test at full weight. I just see national and city parks in my head for that one. Plus, I don't have workout weights anymore. I traded them for a wife. I figured that offered a growth opportunity, rather than workout weights that never change their mass.