|
|
|
|
ride_pow
Jul 13, 2007, 7:03 AM
Post #51 of 121
(15646 views)
Shortcut
Registered: Jul 3, 2007
Posts: 37
|
No materials science degree here. I am not so sure many pure physicists focus on this kind of stuff (too applicable ). However, there are Mechanical Engineers who specialize in fracture mechanics and this stuff is their so called steez. If I remember correctly there are some cases of whole water (or chemical) towers and cargo ships failing. Check this out this pic. It is the type of failure which got people interested in this area I believe. http://www.nrl.navy.mil/...images/hull_ship.jpg These topics are in fact quite interesting and very little was understood even a hundred years ago. I am still working, after seven years and yes they are called doctors, to get my BS in physics and ME. Therefore I am by no means an expert, but I found it amusing the high school physics being thrown around a few posts above mine, which had very little to do with understanding or dispelling so called microfractures. The problem, or rather explanation as I (and obviously a few others), see it is a bit more complicated. The armchair comment was a mild jab. I am sure my english and philosophy buff friends find my ideas on Dostoevsky and Rumi and just as entertaining. Oh and it doesn't stop there. I am sure my Materials prof. would get quite the laugh at my responses to this!
(This post was edited by ride_pow on Jul 13, 2007, 7:09 AM)
|
|
|
|
|
bbirtle
Jul 13, 2007, 9:25 AM
Post #52 of 121
(15635 views)
Shortcut
Registered: Jan 28, 2007
Posts: 102
|
I read through most of that stuff and to save others the pain, here's the bullets: 1) Nobody has evidence from any formal studies except this one - http://www.onrope1.com/Myth1.htm - which says micro fractures aren't a concern with climbing gear based on a few drop tests of carabiners. 2) "Microfractures" are a proven concern in non-climbing domains such as aerospace but whether they affect climbing is so far an rc.com amateur debate. 3) Lots of people have cited personal experience to the affect that it is not a concern i.e. you should inspect incredibly carefully, but it's OK to use dropped gear. Did I miss anything important not summed up above?
|
|
|
|
|
wrbill
Jul 13, 2007, 9:36 AM
Post #53 of 121
(15632 views)
Shortcut
Registered: Dec 5, 2002
Posts: 228
|
ride_pow wrote: Interestingly, to stop crack propagation in aircraft they will often times drill out a hole at the propagating end of the crack. This reduces stress concentration and thus the crack propagation but don't do it with your gear. You are right about the drilling! I am a jet engine mechanic in the Air Force and will do what is called stop drilling of cracks all the time. As for microfractures, yes the are there. Why do you think they do NDI (Nondestructive Inspection) testing on aircraft. This form of testing use a few different types of test: x-ray, mag flex and fluorescent penetrate. A few years back I had drop and OP biner around 170 feet from the top of a route. It hit a rock and bounced. After finding the biner I took it to are NDI lab and they tested it using the floresant pentrent inspection and found no cracks. I asked if they could x-ray it as well and they did. Same finding, no cracks. These inspection were done by people the inspect metal for a living. I use the biner still to this day. Bill
|
|
|
|
|
petsfed
Jul 13, 2007, 10:50 AM
Post #54 of 121
(15622 views)
Shortcut
Registered: Sep 25, 2002
Posts: 8599
|
bbirtle wrote: 3) Lots of people have cited personal experience to the affect that it is not a concern i.e. you should inspect incredibly carefully, but it's OK to use dropped gear. I trusted the BD study. I can't find it though. If you want to wade into the old rec.climbing archives, feel free. But its pretty compelling evidence when you've got dozens of crabs gathered from the base of El Cap (presumably arriving there from being dropped) and the only ones that failed below their rated strength are the ones with poor gate action and/or obvious physical damage. And even then, not all of the obviously damaged crabs failed at below their rated strength. That's about as good as you can hope to get in this case.
|
|
|
|
|
pastprime
Jul 13, 2007, 8:17 PM
Post #55 of 121
(15596 views)
Shortcut
Registered: Jul 7, 2005
Posts: 251
|
This topic has been coming up since I started climbing, which was about 100 years ago. I started to say it had been beaten to death, but obviously we are nowhere near being so fortunate. The first tests I saw done on dropped aluminum climbing gear, including biners, was in the late 1960's. Those tests, and all of the tests done since then, which by now are probably aproaching 100, always; always; always; always; show no loss of strength in gear that is not visibly deformed. I was in the climbing/outdoor industry in the '70's and '80's, and it was common then for the manufacturers to clearly state in their literature that dropping gear would not damage it; now I think they are less likely to say anything that could possibly be distorted and used against them. As recently as four years ago, BD and Omega Pacific did still say in their catalogs that there was no reason to retire dropped gear unless it had perceivable damage, though. And yes, BD did test a bunch of biners and cams from the base of El Cap, some of which were known to have been dropped from near the top, and every one of them that looked ok, was ok. No, I don't have the link. It may have been an email from Chris at BD, rather than something on their website. Yes, repeated flexing-not just loading, but flexing-a very significant distinction- does, eventually, weaken aluminum, but the wing on a plane experiences more flex cycles in one flight through bumpy air than all of the climbing gear on your rack experiences in your lifetime. Quit worrying about it. Deet in bug repellant doesn't hurt your rope, either. Neither does gasoline. There must be some way to not have these things keep coming up every 6 months throughout the ages. Edited to add: and having one piece pull in your anchor or protection system does not increase the load on the remaining pieces beyond what it would have been had that failing piece not been there at all. How many times have these things been discussed? Lots. Isn't there some way, somehow, we can get this out there so it doesn't keep coming up as if the question had neve come up before?
(This post was edited by pastprime on Jul 13, 2007, 8:29 PM)
|
|
|
|
|
pastprime
Jul 13, 2007, 8:41 PM
Post #56 of 121
(15582 views)
Shortcut
Registered: Jul 7, 2005
Posts: 251
|
I do want to say that my complaint is not so much that people are asking these questions, but that there are still so many out there who are always ready to jump in and confidently give an answer that is completely wrong.
|
|
|
|
|
yorb
Jul 13, 2007, 9:23 PM
Post #57 of 121
(15568 views)
Shortcut
Registered: Jun 14, 2004
Posts: 102
|
All questions are continually asked. People aren't going to stop asking how electricity works! ...at least until the baby's start growing up knowing everything to begin with.
(This post was edited by yorb on Jul 13, 2007, 9:25 PM)
|
|
|
|
|
trenchdigger
Jul 13, 2007, 9:53 PM
Post #58 of 121
(15559 views)
Shortcut
Registered: Mar 9, 2003
Posts: 1447
|
squamishdirtbag wrote: So says this german dude I meet in yosemite, and this chick from the creek. I can't think of a reason to disagree, clearly fractures are real but so small they can't me seen? What do you think paranoia or reality? Preface and disclaimer: I'm an engineer with a ME degree and have been working with structural repairs to aluminum and other metals in Navy fighter jets for the past 5 years or so. I'm not what I would consider an expert in the field of fatigue and fracture, but I would say I have a decent background in the subject. Keep in mind that some of my comments below are pure speculation based on my experience and background. Consider it a well-educated guess... Fact: "Microfractures" (or more commonly "Microcracks") do exist and are known to engineers. What is a Microcrack? Basically, a microcrack is a crack too small to see with the naked eye. Microcracks form due to fatigue. What is Fatigue? Fatigue is the progressive, localized, cumulative damage to an object due to repeated loading and unloading at loads below the ultimate strength of the object. If you want an example of Fatigue, take a metal paper clip and bend it back and forth at the same location. After a certain number of cycles, it will eventually fail. The greater the amplitude of the load (stress) applied at each cycle, the less cycles the object will be able to endure before failure. Likewise, smaller loads will result in longer life. The relative amplitude and frequency of applied loads to climbing gear in normal use is so small that failure due to fatigue is not a concern. Can a carabiner break due to fatigue? Sure, a carabiner could conceivably break due to fatigue, but standard use in rock climbing fails to generate the type of cyclic loading necessary propagate fatigue cracks at a fast enough rate to be a danger. A crack large enough to be a fatigue danger would be visible upon careful inspection with the naked eye. Could dropping a carabiner cause Microcracks? No. Microcracks occur as a result of fatigue. Dropping a carabiner COULD damage it enough to make it unsafe for use. Such damage would be apparent under careful inspection. I would not hesitate to use a dropped carabiner that (a)still functions normally and (b)exhibits no visible signs of significant structural damage.
(This post was edited by trenchdigger on Jul 13, 2007, 10:01 PM)
|
|
|
|
|
trenchdigger
Jul 13, 2007, 9:59 PM
Post #59 of 121
(15554 views)
Shortcut
Registered: Mar 9, 2003
Posts: 1447
|
pastprime wrote: ... the wing on a plane experiences more flex cycles in one flight through bumpy air than all of the climbing gear on your rack experiences in your lifetime. Quit worrying about it. I would exchange the words "in one flight" with "in one minute of flight" to further emphasize the point. Good post...
|
|
|
|
|
kzemach
Jul 13, 2007, 10:57 PM
Post #60 of 121
(15542 views)
Shortcut
Registered: Jan 3, 2002
Posts: 30
|
I have personal experience with a fracture breaking a carabiner that I couldn't see. Petzl Spirit, solid gate. Not known to have been dropped (but who knows). Top of aid climb, used it instead of locking biner on my harness to haul the rope through the pulley. Top was slabby, biner was NOT cross loaded. Pulled really hard to get the haul bag up, and BAM, biner broke. What appears to have broken first was the gate ripping out. On solid gate biners, you can't visually inspect where the pin holds the gate to rest of the biner. That part of the biner broke, and thus the pin pulled through and the gate went flying (lost the gate, have the biner somewhere for my museum). Notes: **clearly this biner had some sort of crack or defect, as even with the mechanical advantage of one pulley, my leg press strength isn't 18+ kN. **cannot state if it was a microcrack, or a real crack; being hidden beneith the gate, one would not be able to see it. **If it were a visible crack, that would be an argument for wiregate biners (possible to inspect) **Was going to throw it under the SEM to look for shock vs. fatigue crack propogation and/or possible defect, but never got around to it. **Same climb had a fall on a biner that experinced gate flutter; gate opened a bit when loaded, and the who biner bent open a bit permanantly, but held the fall. So yes, gate flutter happens (solid gate biner).
(This post was edited by kzemach on Jul 13, 2007, 11:03 PM)
|
|
|
|
|
fear
Jul 14, 2007, 2:31 AM
Post #61 of 121
(15528 views)
Shortcut
Registered: Jun 16, 2003
Posts: 475
|
curt wrote: yorb wrote: Does anyone have any links from reputable sources that pretty well dispel this myth. I.E. manufacturers. My school's outdoor program pretty much tells everyone here that micro-fractures occur in aluminum and if you drop something over 15 feet it should be retired. In fact a lot of people who go through the program here come out as "steel" guys, they don't trust it if its not steel... Seek out a school where the instructor's parents aren't also first cousins. Curt He's from West Virginy..... That might not be possible...
|
|
|
|
|
yorb
Jul 14, 2007, 9:23 PM
Post #62 of 121
(15498 views)
Shortcut
Registered: Jun 14, 2004
Posts: 102
|
fear wrote: curt wrote: yorb wrote: Does anyone have any links from reputable sources that pretty well dispel this myth. I.E. manufacturers. My school's outdoor program pretty much tells everyone here that micro-fractures occur in aluminum and if you drop something over 15 feet it should be retired. In fact a lot of people who go through the program here come out as "steel" guys, they don't trust it if its not steel... Seek out a school where the instructor's parents aren't also first cousins. Curt He's from West Virginy..... That might not be possible... I'm actually from Illinois, I just picked a good place to go to school. 30 minutes from the gorge for climbing kayaking and rafting, and 45 minutes from the gauley for kayaking and rafting. Its a really good outdoor program, what you have to realize is, unless the gear manufacturers come right out and say "dropping carabiners does NOT weaken them," then they aren't going to put themselves in a position of possible legal action when or if a carabiner failure resulting in an injury happens. The courts aren't going to care if everyone on RC.com laughs at anyone who mentions microfractures. They are going to ask why you didn't follow the standards. We follow ACCT's standards, which state that if you drop an aluminum carabiner over 15 feet, it must be retired. with my personal gear, I wouldn't retire it, with their gear, I have to. Of course I don't use my personal gear when I'm working.
(This post was edited by yorb on Jul 14, 2007, 9:24 PM)
|
|
|
|
|
knudenoggin
Jul 15, 2007, 4:40 AM
Post #63 of 121
(15461 views)
Shortcut
Registered: May 6, 2004
Posts: 596
|
yorb wrote: My school's outdoor program pretty much tells everyone here that micro-fractures occur in aluminum and if you drop something over 15 feet it should be retired. In fact a lot of people who go through the program here come out as "steel" guys, they don't trust it if its not steel... ... unless the gear manufacturers come right out and say "dropping carabiners does NOT weaken them," then they aren't going to put themselves in a position of possible legal action when or if a carabiner failure resulting in an injury happens. The courts aren't going to care if everyone on RC.com laughs at anyone who mentions microfractures. They are going to ask why you didn't follow the standards. We follow ACCT's standards, which state that if you drop an aluminum carabiner over 15 feet, it must be retired. This topic arose in a tree-climbing forum (tci-forums.com) shortly after it was touched upon in a canyoneering one, where Tom Jones, one-time BD engineer, attempted to put the myth to rest. Apparently there are some authorities who require retirement on what to the eyes of most contributers in RC.com must seem like ridiculous grounds. My reading of the discussion (alas, so poorly presented that one cannot easily discern speakers in the exchange (attribution v. response)) recommended by Tigerlily at the SARinfo site (http://www.sarinfo.bc.ca/...uipment/binerlif.eqp) is that it stands in some contradiction of expert arguments denying the microcrack myth!? (Simply, at least: they DO vs. do NOT exist ; next issue, propagation and practical effect, & visual signficance/detection.) Below is my echo of Tom's reply into the TCI Forum, where at one point, it was suggested that, for beginners, a 3' threshold on drops was reasonable(!!). ( http://www.tci-forums.com/...?tid=1154&page=1 )
In reply to: In reply to: Originally posted by SRT-Tech Biners are not designed to be used as a throw weight!! and this is something that i CONTINUALLY see in treeclimbing, be it Rec or Pro.....gear that is used wrong, abused or used for something OTHER than its INTENDED purpose. [..] i'm not singling out anyone here or any forum in particular, but there is a real need for treeclimbers (any/all) to come up to par with the rest of the rope access world, in terms of basic do's / don'ts related to our gear. There is pushing the boundaries in terms of new techniques or gear, then there is abuse of your LIFE SUPPORT gear. Choose one. Wow, "to come up to par with the rest of rope access world," indeed! While rockclimbers might prefer NOT to be thought of as rope access --they climb rock, with rope sometimes not even used--, it was in their activity that carabiners were developed. And while rockclimbers have no exact use to throwing 'biners about, the metal can be slammed hard into the rock on a fall as the ropes snap taut. Need I point out that rock is much, much harder than a tree (anyone climbing ebony?)? Recently, in another rope-access sort of endeavor, the old tired myth of microfractures arose, and drew this authoritative response from one who worked for over a decade in the gear side of climbing--to wit --------quote: Neither the steel used in carabiners nor the aluminum alloys is subject to micro-cracking. There may be over-heat treated steel or titanium alloys that exhibit it, but the theory of micro-cracking only came up when they started using fancy ceramics for jet engine turbines. You can drop your carabiners thousands of feet onto granite, and if they still open and close smoothly, they are fine to use. If you feel uncomfortable with this advice, then go ahead and retire them, or send them to me. Can I prove this? There is an engineering argument - aluminum alloys (might be exceptions, but 7075-T6 is not one of them) and ordinary steel alloys (as used in carabiners) are not the type of material that exhibits micro-cracking. There is an evidence argument - while working at Black Diamond for 12 years, we NEVER saw a carabiner that exhibited any form of micro-cracking or loss of strength from being dropped (while still functional), including quite a few dropped the full height of El Cap (3000 feet). But no, I cannot PROVE that all biners over all time will never exhibit loss of strength. And just to cover all the bases, carabiners dropped from outer space, on re-entry, will heat up substantially which will screw up the heat treating. There will likely be ablation of material off the outside also, so I advise against using biners that are dropped from outer space. Those should definitely be retired. Perhaps Brian knows of some examples of hidden micro-cracking in conventional alloys. ... -------end quote. So, should the old adage "trees don't grow to heaven" be proved false, THEN one might be concerned about dropping a 'biner; but doing so in more mortal ways won't cause you to get to heaven. *knudeNoggin* It seems to me that the microcrack supporters stand in need of some test evidence for their side of the issue: some sequences of drop tests both of the oops, there goes my 'biner sort and the UIAA sort (fall holding) after which x-ray or other detection of a microcrack is made, and then some further stressing w/cyclic loading to monitor the discovered crack. So far, to my eyes, it is just the possibility of this that is advanced--no citation of it occurring. *kN* ps: Someone mentioned gasoline & ropes as another myth: when I raised this to (IIRC) Beal & also w/Clyde Soles, their response was, yes, GAS in a pure form isn't damaging, but less is known about the myriad additives that might come along for the ride with common gasoline. pps: Some of OnRope1's Mythbusters are themselves busted--i.p., the one about the Figure8 knot & orientation, which apparently refers to an assertion made in Dave Merchant's Life on a Line (new ed.); OnRope1 needs to compare knot images better!
|
|
|
|
|
reno
Jul 15, 2007, 3:02 PM
Post #64 of 121
(15441 views)
Shortcut
Registered: Oct 30, 2001
Posts: 18283
|
knudenoggin wrote: It seems to me that the microcrack supporters stand in need of some test evidence for their side of the issue YES! EXACTLY! For those who say that microfractures DO exist, please show us the proof. It's like the Loch Ness monster, Big Foot, UFO/Aliens, and intelligent liberals: There is no proof of their existence, but everyone thinks it's true.
|
|
|
|
|
Valarc
Jul 15, 2007, 3:22 PM
Post #65 of 121
(15437 views)
Shortcut
Registered: Apr 20, 2007
Posts: 1473
|
petsfed wrote: You know, I've never actually met a practicing materials physicist. Plenty of materials engineers and quite a few chemists. But no physicists that actually study how materials respond to load. Oh, we exist - we just study more interesting materials. Steel and aluminum are boring, but give me some glassy colloids or shear thickening viscoelastic polymers and I'll do rheology 'till the cows come home.
|
|
|
|
|
adatesman
Jul 15, 2007, 4:57 PM
Post #66 of 121
(15427 views)
Shortcut
Registered: Jul 13, 2005
Posts: 3479
|
|
|
|
|
|
Valarc
Jul 15, 2007, 5:21 PM
Post #67 of 121
(15420 views)
Shortcut
Registered: Apr 20, 2007
Posts: 1473
|
That is, by far, my favorite video to show people when I'm trying to explain what I do. One of these days I'm going to set up that "experiment" as a demo for undergrads. And now I'd say this thread is officially hijacked.
|
|
|
|
|
curt
Jul 15, 2007, 6:31 PM
Post #68 of 121
(15413 views)
Shortcut
Registered: Aug 27, 2002
Posts: 18275
|
Valarc wrote: petsfed wrote: You know, I've never actually met a practicing materials physicist. Plenty of materials engineers and quite a few chemists. But no physicists that actually study how materials respond to load. Oh, we exist - we just study more interesting materials. Steel and aluminum are boring, but give me some glassy colloids or shear thickening viscoelastic polymers and I'll do rheology 'till the cows come home. My background is in materials science as well, but is focused on compound semiconductor materials like gallium arsenide. I'm with you--who wants to study Al? Curt
|
|
|
|
|
coastal_climber
Jul 15, 2007, 9:45 PM
Post #69 of 121
(15387 views)
Shortcut
Registered: Nov 17, 2006
Posts: 2542
|
Sure. I just dropped a couple biners half a pitch, and I checked the gates and re-racked them. >Cam
|
|
|
|
|
trenchdigger
Jul 16, 2007, 3:21 PM
Post #70 of 121
(15331 views)
Shortcut
Registered: Mar 9, 2003
Posts: 1447
|
reno wrote: knudenoggin wrote: It seems to me that the microcrack supporters stand in need of some test evidence for their side of the issue YES! EXACTLY! For those who say that microfractures DO exist, please show us the proof. It's like the Loch Ness monster, Big Foot, UFO/Aliens, and intelligent liberals: There is no proof of their existence, but everyone thinks it's true. Considering the fact that google search results in 162,000 hits for "fatigue microcracks", and none of them are urban legend websites debunking them as myths, I think the mighty internet safely proves they're a real phenomenon. After all, if it's on the internet, it must be true. Another test would be to read any engineering text book dealing with fatigue. You'll find it there too... Are they a danger in climbing equipment? See my post above for my opinion...
(This post was edited by trenchdigger on Jul 16, 2007, 3:22 PM)
|
|
|
|
|
stymingersfink
Jul 16, 2007, 9:11 PM
Post #71 of 121
(15296 views)
Shortcut
Registered: Aug 12, 2003
Posts: 7250
|
curt wrote: Valarc wrote: petsfed wrote: You know, I've never actually met a practicing materials physicist. Plenty of materials engineers and quite a few chemists. But no physicists that actually study how materials respond to load. Oh, we exist - we just study more interesting materials. Steel and aluminum are boring, but give me some glassy colloids or shear thickening viscoelastic polymers and I'll do rheology 'till the cows come home. My background is in materials science as well, but is focused on compound semiconductor materials like gallium arsenide. I'm with you--who wants to study Al? Curt Especially since all the legwork has already been done by Boeing. Think they recommend the retirement of their planes after every hard landing? Me either.
|
|
|
|
|
chriss
Jul 17, 2007, 4:42 AM
Post #72 of 121
(15269 views)
Shortcut
Registered: Jul 13, 2004
Posts: 92
|
shimanilami wrote: chriss wrote: shimanilami wrote: greenketch wrote: It is true that the forces are higher in catching a fall. That can't be right. The shock force when a piece of gear strikes rock (e.g. talus at the base of a climb) is incredibly high. Just consider removing a pin. You can jump up and down on the thing all day long - even with a static sling - and it won't budge, but a few taps with a hammer can knock it right out. The impact force is much higher when there is no elasticity in the system. Interesting. Think of a carabiner hitting a rock. How much force? F=MA or F=1/2*M*V^2 where V(final)=0 If F= say 8 KN (a random fall force) and M=100g or .1Kg (a big carabiner) then V=400 M/S or .25 miles/S (approx) or 900 mph (approx) I don't know the terminal velocity of a carbiner. So if you hear that 'biner hit mach 1 don't reuse it. But you don't know the orientation of the impact. So inspect it and move on. chris Actually, E (not F) = 1/2 * m * V^1/2. Your math is wrong. But let's pursue this line of analysis anyway to see if my empirical evidence measures up. First, energy is not the right measure to apply. In a fall, kinetic energy is absorbed by the rope and its friction against 'biners in the system. The top piece doesn't move appreciably, so beyond friction not much energy is absorbed by the top piece. The more appropriate measure when talking about microfractures is force or, perhaps even more appropriately, pressure. We can accept 8kN as reference for the force exerted on the top piece’s carabiner (while it seems high, I don’t have the necessary data to refute it), but what about a dropped carabiner? Consider a 100g carabiner which strikes talus at 10m/s (the speed incurred by a 15 foot drop). E = ˝ * m * V^2 = .5 * 0.1kg * (10m/s)^2 = 5 kgm^2/s^2 If this energy is absorbed within a millimeter (a rough estimation of the distance required to slow from 10m/s to a stop, and we’ll ignore elasticity), then F = E / d = (5 kgm^2/s^2) / 0.001m = 5,000 kgm/s^2 = 5kN Thus, the force applied to a carabiner dropped from 15 feet is about the same as the force experienced by the top carabiner in a fall. (To be more precise, a carabiner dropped from 20 feet will experience ~8kN of force.) There is a major difference, however, in how the force is distributed. In a fall, the force is spread across the surface of the ‘biner that contacts the rope. I’d estimate that the effective surface area is at least 50mm^2. A dropped carabiner, in contrast, experiences all its force at a point, perhaps 1mm^2. Thus, the pressure exerted at the point of contact – where deformation and, thus, microfractures would originate – is many times higher with a carabiner dropped from 20 feet. And a carabiner dropped from hundreds of feet would experience forces several orders of magnitude greater. Wow. I took a few shortcuts all right. But lets not over do this. My numbers are correct. F=MA integrated to dt where t--->0 F=1/2 M V^2 if Vfinal=0 Assuming the rock didn't deflect, it would take a force equal to that of the biner. Check your equations first. Energy has a time component. sky7high is right W=FD. No time constraint. chris
|
|
|
|
|
timfu
Jul 17, 2007, 6:12 AM
Post #73 of 121
(15253 views)
Shortcut
Registered: Jul 17, 2007
Posts: 5
|
chriss wrote: Wow. I took a few shortcuts all right. But lets not over do this. My numbers are correct. F=MA integrated to dt where t--->0 F=1/2 M V^2 if Vfinal=0 Assuming the rock didn't deflect, it would take a force equal to that of the biner. Check your equations first. Energy has a time component. sky7high is right W=FD. No time constraint. chris Back to high school phyisics - F does not equal 1/2mv^2, However, the integral of Fdt is equal to the total energy-1/2mv^2, thus the integral of Fdt is referred to as the potential energy... Not convinced, think about units - force has units of Newtons and mv^2 has units of joules...
|
|
|
|
|
bbirtle
Jul 17, 2007, 10:11 AM
Post #74 of 121
(15245 views)
Shortcut
Registered: Jan 28, 2007
Posts: 102
|
various wrote: ...My numbers are correct. F=MA integrated to dt where t--->0 F=1/2 M V^2 if Vfinal=0 ...Back to high school phyisics - F does not equal 1/2mv^2, ... Could you nerds please either STFU or at least provide a non-technical summery of whatever the hell you're talking about (and how it's actually relevent) when you post crap like this? I just want to know if my biner is going to kill me if I keep using it after it's dropped and all this math is making my head hurt.
(This post was edited by bbirtle on Jul 17, 2007, 10:13 AM)
|
|
|
|
|
Valarc
Jul 17, 2007, 12:50 PM
Post #75 of 121
(15224 views)
Shortcut
Registered: Apr 20, 2007
Posts: 1473
|
chriss wrote: I took a few shortcuts all right. But lets not over do this. My numbers are correct. F=MA integrated to dt where t--->0 F=1/2 M V^2 if Vfinal=0 Please note: this reply is coming from an actual physicist, as in someone who publishes research in physics, who has taught physics classes at the college level at two different universities. You. are. wrong. You're making one of the mistakes my students have made a thousand times - NOT CHECKING YOUR UNITS. It's really easy to see whether you're wrong or not before you shove your foot in your mouth and insist you know what you're talking about. Let's analyze your so-called force equation using unit analysis. force (newtons, ie kilograms * meters / seconds^2) 1/2 m * v^2 (kilograms * meters^2 / seconds^2) Any equation where the units on the left hand side of the equals sign don't match the units on the right hand side is completely and utterly worthless. You are wrong, and if you were my student I'd fail you just for being a know-it-all jackass (trust me I've seen plenty of those)
|
|
|
|
|
|
|
|
|