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shameless pleading





Rope burning

And how to measure time with fire.

Dear Word Detective: If one of us kids would go to my Mom with an idea about something, she would say, “I thought I smelled rope burning.” My feeling is she didn’t even know the full meaning of what she was saying. So, I would like to know what the basis is for that phrase. — Faith.

Hmm. I wouldn’t assume that your mother didn’t know what she was saying. Given that you’re walking around and writing grammatically coherent sentences, my guess is that she did.

Speaking of ropes, I came across an interesting logic problem involving burning ropes awhile back. I’m afraid I don’t know who wrote this rendition of it, but it’s a neat puzzle: “You are given two ropes and a lighter. This is the only equipment you can use. You are told that each of the two ropes has the following property: if you light one end of the rope, it will take exactly one hour to burn all the way to the other end. But it doesn’t have to burn at a uniform rate. In other words, half the rope may burn in the first five minutes, and then the other half would take 55 minutes. The rate at which the two ropes burn is not necessarily the same, so the second rope will also take an hour to burn from one end to the other, but may do it at some varying rate, which is not necessarily the same as the one for the first rope. Now you are asked to measure a period of 45 minutes. How will you do it?”

My answer would be “Sell the rope and buy a cheap watch,” but I’ll give the real solution in a minute. Meanwhile, back at what your mother said, I think there are a number of possible explanations. There is, for instance, an “app” for the iPhone called “Burn the Rope,” a game in which you try to keep a virtual rope on fire. I know, I know, your mom said “I thought I smelled rope burning” when you were kids, but perhaps she was a time traveler from the future.

It’s probably more likely that your mother was facetiously implying that by thinking too hard you kids were overheating your brains and producing an imaginary odor. When I was a kid, it was considered fairly clever, when someone announced “I’ve been thinking,” for the schoolyard wit to respond, “I thought I smelled something burning.” Your mother’s specific reference to “rope burning” may have been a reference to the fact that burning rope produces an acrid, unpleasant odor. “Rope,” in fact, has been slang for cheap tobacco (especially in the form of low-quality cigars) since the 19th century (“The smoke of his cheap tobacco drifted into the faces of the group?. ‘If you’ve got to smoke rope like that, smoke it in a crowd of muckers; don’t come here amongst gentlemen’,” 1899).

It is possible, however, that your mother was jokingly implying that you’d been setting fire to something a bit more illicit than either rope or cheap tobacco. “Rope” has been slang for marijuana since at least the 1940s (“Detectives from the CIB Drug Squad in Brisbane are becoming quite familiar now with words like muggles, griefs, mezz, Mary Jane, jive, tea, rope and loco-weed,” 1972). Drug slang is often hard to explain (“griefs”?), but the logic for “rope” in this sense is obvious. The strong fibers of the hemp plant (cannibis sativa) have been used in the production of rope (as well as fabric, paper and many other things) for centuries, but the “indicia” subspecies of cannibis sativa is best known as the source of marijuana. Your mother, I hasten to point out, would not have had to be a pothead to be familiar with the slang term.

And now, the answer as to how to measure 45 minutes with burning rope: Light rope #1 at one end, and simultaneously light rope #2 at both ends. When rope #2’s ends meet, light rope #1 at the other end. Thirty minutes have been measured so far, leaving 30 minutes left on rope #1. When rope #1’s ends meet, fifteen minutes have been measured, for a total of 45 minutes (which is probably just long enough for the DEA to show up and kick in your door).

6 comments to Rope burning

  • Hale

    Thanks so much for this post – my friends really enjoyed this puzzle also.

    Found a great answer here as well:

    2 Ropes 45 Minutes

  • Akshay Mone

    I am sorry but i think This is wrong answer. when it is said that it does not burn at uniform speed how can you expect a half rope to be burn in 30 minutes only. It can be case that half rope is burnt in 1 min and other half takes 59 minutes to burn.

  • Mohit

    Agree with Akshay. Can anyone please explain the answer a bit more who feels that this is the correct solution. Thanks.

  • Nick

    I agree with Akshay and Mohit. Please explain why rope #2 would burn in 30 minutes. It’s not enough to note that 60/2 = 30!

  • Sean

    The rope may burn at any rate, but burning twice as fast (i.e. burning from both ends) at any combination of rates equalling one hour total will then equal half an hour total. The same is true of the remaining half-hour’s worth of rope #1.

  • Hazel

    I think the rope-burning connection to thinking has more to do with work as people handled work at the time. You are thinking very hard, but your thinking is so simple that you are using a rope on a pulley to lift your thoughts, and you are working so hard at thinking, hoisting your thoughts, that the rope is burning.

    It’s similar to saying that a person trying to solve a problem is “banging his rocks together really hard.”

    In the early 1900s, one might say a person couldn’t think of an answer if he thought it through with both hands for a fortnight.

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