# Monkey on a rope, I'm the monkey. Real world. **URL:** \ **Category:** Factual Questions\ **Created:** [August 17, 2013, 7:22pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506 "2013-08-17T19:22:31Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [August 18, 2013, 2:22am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/21 "2013-08-18T02:22:31Z")
> [@ZenBeam](#): > > Say you had 100 feet of rope, so you’re hanging 100/2 = 50 feet below the pulley. Pull the rope by 1 foot, and you’ve got 99 feet of rope (plus the dangling 1 foot). So now you’re 99/2 = 49.5 feet below the pulley. Absolutely right. I withdraw my objection and smack myself for not noticing this before I opened my mouth. :smack: [QUOTE=md2000] I was about 220lb (diet starts next week) and the skinny guy at the other end could not have been more than 190lb. When I reached for a handhold, missed, and slipped and dropped, he was yanked about 5 feet into the air. The only reason he did not keep going was a practical one - the rope was looped through a ring at the top of the escarpment, and running on a thick folded blanket up there (to prevent chafing and abrasion). So friction stopped him… and me. [/QUOTE] That strikes me as something wrong with your setup. My girlfriend is half my weight and has no trouble belaying me without ever leaving the ground. Gym walls and outdoor hitches are meant to have enough friction to prevent that situation. ---
**Author:** ![svd678](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@svd678](https://boards.straightdope.com/u/svd678)\ **Post date:** [August 18, 2013, 3:19am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/22 "2013-08-18T03:19:21Z")
The "relative to you"part is a red herring. If you pull down 1 foot on one end, the other goes up 1 foot. Its a 1 to 1 relation, no mechanical advantage. Altho there might be some help since pulling down on the rope lightens the weight, I think. ---
**Author:** ![svd678](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@svd678](https://boards.straightdope.com/u/svd678)\ **Post date:** [August 18, 2013, 3:24am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/23 "2013-08-18T03:24:09Z")
If you pull 1 foot of rope thru the pulley you have 51 ft on the down side, 49 on the up side, not 49 and a half. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 18, 2013, 3:30am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/24 "2013-08-18T03:30:34Z")
But if you pull one foot through your hands, you’re only pulling six inches through the pulley. ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [August 18, 2013, 4:50am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/25 "2013-08-18T04:50:14Z")
Hmm- but the six inches through the pulley is all the rope has moved along its length. If I moved the rope on the other side down six inches relative to the ground and the pulley, don’t I go up six inches? ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [August 18, 2013, 5:21am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/26 "2013-08-18T05:21:12Z")
You are mixing up where you are measuring the length of rope. 6 inches _at the load_ = 3 inches _pulled past the pulley_. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 18, 2013, 11:57am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/27 "2013-08-18T11:57:00Z")
> [@](#): > > If I moved the rope on the other side down six inches relative to the ground and the pulley, don’t I go up six inches? Yes. But why is that relevant? ---
**Author:** ![slm2955](https://avatars.discourse-cdn.com/v4/letter/s/c6cbf5/32.png) [@slm2955](https://boards.straightdope.com/u/slm2955)\ **Post date:** [August 18, 2013, 11:57am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/28 "2013-08-18T11:57:52Z")
Because it is. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [August 18, 2013, 12:05pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/29 "2013-08-18T12:05:39Z")
> [@slm2955](#): > > Because it is. Not to the physics of the situation it isn’t. Hang your weight in cabbage from a rope that goes over a pulley. Pull the rope down a foot. Cabbage goes up a foot. Work done = 1 you-foot Hang your own weight from that rope and pull the rope down a foot relative to you. You go up six inches. Work done = 1/2 you-foot To disprove this, a sound explanation based in Newtonian physics which explains the reality described by the OP, you need more than “because it is”. ---
**Author:** ![slm2955](https://avatars.discourse-cdn.com/v4/letter/s/c6cbf5/32.png) [@slm2955](https://boards.straightdope.com/u/slm2955)\ **Post date:** [August 18, 2013, 12:07pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/30 "2013-08-18T12:07:14Z")
No I don’t ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [August 18, 2013, 12:42pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/31 "2013-08-18T12:42:20Z")
We can’t help people with willful ignorance here… ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [August 18, 2013, 1:37pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/32 "2013-08-18T13:37:14Z")
> [@Chronos](#): > > You are exerting a force equal to half of your weight on the rope you’re pulling. Since the pulley at the top has low friction and the rope is light, there’s the same amount of tension everywhere in the rope. The rope is attached to you at two points: At your harness, and at your hands where you’re pulling. At each of those two points, it’s exerting a force on you equal to half of your weight. Half your weight plus half your weight is your full weight, so the force is enough to lift you. This is all that really needs to be said on the matter, rather than relying on intuition or rules of thumb based on lengths of rope that may or may not apply to this particular situation. ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [August 18, 2013, 6:08pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/33 "2013-08-18T18:08:09Z")
If it was, me, I think this drawing might be more accurate: ```auto Before: After O O | | | | | | | | | | | | | | | | | | | | | |Me | | \_|O Aaaaaaaaaaaaahhhh! / | ``` ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 18, 2013, 10:41pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/34 "2013-08-18T22:41:53Z")
Ah. In that case, you are doing no work at all, but merely converting some quantity of gravitational potential energy into an equal amount of kinetic energy. ---
**Author:** ![Arthur\_See\_Clarity](https://avatars.discourse-cdn.com/v4/letter/a/d9b06d/32.png) [@Arthur\_See\_Clarity](https://boards.straightdope.com/u/Arthur_See_Clarity)\ **Post date:** [August 19, 2013, 1:30am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/35 "2013-08-19T01:30:41Z")
well I don’t know about slm, but in my case ignorance fought! In fact I’m kind of embarrassed I couldn’t figure that out on my own. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [August 19, 2013, 3:13am UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/36 "2013-08-19T03:13:44Z")
> [@leahcim](#): > > My girlfriend is half my weight and has no trouble belaying me without ever leaving the ground. Call her out on the weight lie. 😃 ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [August 19, 2013, 4:47pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/37 "2013-08-19T16:47:53Z")
There’s a REAL easy way to answer this. If you have to pull 1 foot to raise 1 foot, there’s no mechanical advantage. A stationary person would have to pull one foot to go up one foot. But in your case, if you pull one foot of rope past _you_, you’ve only risen 6 inches. The rope you’re pulling came down 6 inches; you went up 6 inches. Ergo, mechanical advantage of 2. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [August 19, 2013, 4:57pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/38 "2013-08-19T16:57:08Z")
I see **Chronos** and **ZenBeam** beat me to it. I particularly like Chronos’s point about each segment of the rope holding half your weight. > [@svd678](#): > > The "relative to you"part is a red herring. If you pull down 1 foot on one end, the other goes up 1 foot. Its a 1 to 1 relation, no mechanical advantage. Altho there might be some help since pulling down on the rope lightens the weight, I think. Not at all a red herring. A person on the ground wouldn’t get any mechanical advantage lifting a dead weight, but the person hanging on the rope gets advantage by lifting his own weight. He has to pull two feet of rope to get one foot higher. What clearer evidence of mechanical advantage could we want? > [@slm2955](#): > > No I don’t Brilliant rhetoric. I’m convinced. Ignore my previous comments. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [August 19, 2013, 5:04pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/39 "2013-08-19T17:04:23Z")
> [@leahcim](#): > > That strikes me as something wrong with your setup. My girlfriend is half my weight and has no trouble belaying me without ever leaving the ground. Gym walls and outdoor hitches are meant to have enough friction to prevent that situation. It depends on how far you fall. If the belayer keeps little slack, the weight difference can be pretty substantial without going flying. If there’s a lot of slack, the faller can gain enough momentum to lift someone. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [August 19, 2013, 6:44pm UTC](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506/40 "2013-08-19T18:44:38Z")
> [@leahcim](#): > > … > That strikes me as something wrong with your setup. My girlfriend is half my weight and has no trouble belaying me without ever leaving the ground. Gym walls and outdoor hitches are meant to have enough friction to prevent that situation. Nothing wrong. Works as advertised. A significantly heavier weight falls several feet before stopping; the yank on the rope lifts him from a lying back position to a few feet in the air before he stops (friction). Then as I get handholds and pull myself up a bit, the slack allows him to lower to the ground. perhaps there was a bit too much slack but I did not want to be “hanging” off the rope. Added to that, I was lunging up (and sideways) for a hold, so he had no time to reel in the added slack. But this is the answer to the OP’s question. In the real world, there is a LOT of friction, it’s designed into the system for precisely the reason you mention (and I demonstrated). The goal is to stop motion within a few feet, not to experiment with physics. Whereas, in the reel world, there is no friction and the heaviest load sinks to the ground. [Previous page](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506.md?page=1) [Next page](https://boards.straightdope.com/t/monkey-on-a-rope-im-the-monkey-real-world/666506.md?page=3)