# Magician crossing bridge. **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [July 4, 2014, 10:31am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335 "2014-07-04T10:31:41Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 9, 2014, 3:35pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/21 "2014-07-09T15:35:08Z")
> [@Patch](#): > > Out of curiosity, has anyone ever juggled heavy objects while standing on a scale to demonstrate the puzzle? The problem is that all ordinary scales are “bouncy” in some way. The traditional analog ones really bounce. Even digital scales will have some spring to them. The doctor’s office style upright scales can’t handle quick changes in force either. I just checked our digital scale and it would register the weight, blink and then freeze. No further change until you get off. On an old fashioned analog scale you’ll see the numbers jiggle around and not be able to tell what’s actual additional force and what’s overshoot. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [July 9, 2014, 3:39pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/22 "2014-07-09T15:39:19Z")
> [@Senegoid](#): > > _In any case, this problem remains, and I put it to The Straight Dope community to solve it: How, then, should the problem be stated in the first place?_ I’m not sure there’s any good way to state the question because it’s based on a broken premise. Juggling is not a solution to any problem I can think of. Any other solution (like carrying them one at a time or using any true form of magic) is so trivial that it’s hardly a riddle at all. So, really, we have to start at square one and completely redesign the riddle from the ground up. We need both a new question and a new answer. The obvious options all boil down to questions about foxes and geese and cabbage (or whatever) that eliminate the obvious answer of taking things over one at a time. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [July 9, 2014, 5:06pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/23 "2014-07-09T17:06:04Z")
> [@idebbi](#): > > first thing that came to my mind was the old riddle about the farmer, the fox, the goose and the cabbage having to cross the river in a boat that won’t hold them all…(and by the way the fact that the guy was a farmer didn’t have any bearing on the solution)… This conundrum was alluded to in the recent FX miniseries _Fargo_, as it happens. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [July 9, 2014, 5:12pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/24 "2014-07-09T17:12:56Z")
> [@ftg](#): > > I just checked our digital scale and it would register the weight, blink and then freeze. No further change until you get off. And then it will only decrease the weight by 10 grams or so. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [July 9, 2014, 6:34pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/25 "2014-07-09T18:34:45Z")
> [@runningdude](#): > > As a civil engineer, I would just like to point out that if the bridge has a “capacity” of 68 kg, then its actual capacity would be be at least 204 kg (factor of safety). Maybe when built, but the local farmers have been running their 190 kg haywains across it for 30 years … “implement of husbandry” exemption from weighmaster jurisdiction. > [@ftg](#): > > On an old fashioned analog scale you’ll see the numbers jiggle around and not be able to tell what’s actual additional force and what’s overshoot. I tried this, but the scales are a bit heavy and bulky. Very difficult to catch, so all three are broken now. * * * Coins are round? Just roll one across and chase after it. ---
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [July 9, 2014, 8:04pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/26 "2014-07-09T20:04:04Z")
> [@dracoi](#): > > I’m not sure there’s any good way to state the question because it’s based on a broken premise. Juggling is not a solution to any problem I can think of. Simultaneously carry three balls, using only your hands, across a bridge without letting them touch each other. Powers &8^] ---
**Author:** ![Larry\_Borgia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/larry_borgia/32/156_2.png) [@Larry\_Borgia](https://boards.straightdope.com/u/Larry_Borgia)\ **Post date:** [July 10, 2014, 12:35am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/27 "2014-07-10T00:35:52Z")
> [@psythe](#): > > [Original Thread](http://www.straightdope.com/columns/read/1224/riddle-me-this-how-can-68-3x1-70) > > Two options spring to mind. > > 1.) Take the gold coins over one at a time. No-one said you couldn’t do that. > > 2.) Cast a spell to make the gold weightless. He’s a goddamn magician, after all. I read the riddle as him being a stage magician; No supernatural powers, just sleight of hand and dexterity. ---
**Author:** ![jezzaOZ](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jezzaOZ](https://boards.straightdope.com/u/jezzaOZ)\ **Post date:** [July 10, 2014, 3:04am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/28 "2014-07-10T03:04:44Z")
It’s quite easy using juggling and no forces are exceeded. Standing at the bridge threshold, put two bars in your pocket and toss the third up in the air and along the bridge. Run smartly to the other side and catch the tossed bar. It’s a form of juggling and no extra forces are encountered on the bridge. However the entire premise is ridiculous because no-one has considered dynamic forces from walking or running. Simply taking a step involved accellerating most of your mass upwards. Your nett ‘weight’ will always exceed your static weight. both at the launch of a step and the fall of foot at the end of the step. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 10, 2014, 6:50am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/29 "2014-07-10T06:50:53Z")
> [@jezzaOZ](#): > > However the entire premise is ridiculous because no-one has considered dynamic forces from walking or running. Simply taking a step involved accellerating most of your mass upwards. Your nett ‘weight’ will always exceed your static weight. both at the launch of a step and the fall of foot at the end of the step. That’s true, but I think the dynamic forces from walking, in itself (and without taking into account the weight of the gold bricks), does not exceed the stated capacity of the bridge. But with the weights of the bricks included, then probably so. The dynamic forces of tossing and catching the bricks is the problem being discussed here, which the original problem (as stated) doesn’t take into account. Your problem of the dynamic forces of walking in itself, is probably even less often thought of, let alone considered, and thus hardly ever mentioned. When that “magician” sets forth upon that bridge, _he’s gonna die!_ Have you seen our thread from last March [about the dynamics of climbing a Stairmaster](http://boards.straightdope.com/sdmb/showthread.php?t=718116)? It took us a long time (well, it took _me_ a long time) to get my head wrapped around the forces of that. ---
**Author:** ![jezzaOZ](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jezzaOZ](https://boards.straightdope.com/u/jezzaOZ)\ **Post date:** [July 11, 2014, 2:10am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/30 "2014-07-11T02:10:01Z")
> [@Senegoid](#): > > Your problem of the dynamic forces of walking in itself, is probably even less often thought of, let alone considered, and thus hardly ever mentioned. I brought it up as I’ve just returned from a trek in the rainforest where crossing rickety bridges over raging torrents is the norm. Every step on them causes them to sway and shake most alarmingly - suspension bridges being by far the worst. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 11, 2014, 6:14am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/31 "2014-07-11T06:14:27Z")
> [@jezzaOZ](#): > > I brought it up as I’ve just returned from a trek in the rainforest where crossing rickety bridges over raging torrents is the norm. Every step on them causes them to sway and shake most alarmingly - suspension bridges being by far the worst. Obvious question: Did you encounter any feral magicians in the wild, slinging gold bricks? ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [July 12, 2014, 8:55am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/32 "2014-07-12T08:55:32Z")
What the original question fails to take into account is that the magician is actually a _mentalist_, not a sleight-of-hand expert. So he starts throwing the gold pieces (a 1 kg chunk of gold is fairly substantial) and immediately drops two over the sides of the bridge. Oops, but at least now he can walk across the bridge safely. I just don’t see the obvious connection of magician = juggler. I presume the reason he doesn’t just take them one at a time is that while he’s walking the first piece across, bandits jump out of hiding and steal his other two gold bars and run off. Sure, the bandits are unstated in the problem statement, but the riddle is crap anyway. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [July 12, 2014, 12:30pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/33 "2014-07-12T12:30:42Z")
> [@Senegoid](#): > > Obvious question: Did you encounter any feral magicians in the wild, slinging gold bricks? He should have checked for gold bricks beneath that one, broken bridge… ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 12, 2014, 5:47pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/34 "2014-07-12T17:47:39Z")
> [@Irishman](#): > > I presume the reason he doesn’t just take them one at a time is that while he’s walking the first piece across, bandits jump out of hiding and steal his other two gold bars and run off. Sure, the bandits are unstated in the problem statement, but the riddle is crap anyway. No, I think the goat eats them. But if he takes the gold brick(s) across first, then the chicken eats the goat. ---
**Author:** ![Blackfaer](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@Blackfaer](https://boards.straightdope.com/u/Blackfaer)\ **Post date:** [July 15, 2014, 7:58pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/35 "2014-07-15T19:58:59Z")
> [@njtt](#): > > I think you mean either African or European **swallows**. Well, the African swallows are non-migratory, so where is this bridge exactly? And the European swallows are too small, it’s a simple matter of weight ratios. Perhaps if two swallows carried it between them on a string? Perhaps the magician is an alchemist, so he’ll turn the Gold into something that weighs less, like Aluminum… Oooh, I’ve got it! He saws himself in half, and the lower half walks over with the bricks, then the upper half uses his arms to drag himself across, where he puts himself back together! ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [July 15, 2014, 8:08pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/36 "2014-07-15T20:08:23Z")
> [@Blackfaer](#): > > Well, the African swallows are non-migratory, so where is this bridge exactly? And the European swallows are too small, it’s a simple matter of weight ratios. Perhaps if two swallows carried it between them on a string? Or you might employ a whole flock of swallows with strings, [like this dude does here](http://www.wisdomportal.com/Levitation/LittlePrinceBirds%28571x850%29.jpg). ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 15, 2014, 9:20pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/37 "2014-07-15T21:20:09Z")
> [@Blackfaer](#): > > Oooh, I’ve got it! > > He saws himself in half, and the lower half walks over with the bricks, then the upper half uses his arms to drag himself across, where he puts himself back together! I like the way you think. Which sort of frightens me. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [July 16, 2014, 9:50pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/38 "2014-07-16T21:50:25Z")
Gold is easily convertible to paper currency, so he deposits the gold before crossing the bridge, carries the bank note across and has the money wired to the other side, where he converts it back to gold. ---
**Author:** ![CorpusDelecti](https://avatars.discourse-cdn.com/v4/letter/c/a3d4f5/32.png) [@CorpusDelecti](https://boards.straightdope.com/u/CorpusDelecti)\ **Post date:** [July 19, 2014, 9:09am UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/39 "2014-07-19T09:09:31Z")
He should remove the white rabbit from his top hat and put some of the gold there. ---
**Author:** ![davidm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidm/32/225_2.png) [@davidm](https://boards.straightdope.com/u/davidm)\ **Post date:** [October 24, 2014, 10:23pm UTC](https://boards.straightdope.com/t/magician-crossing-bridge/692335/40 "2014-10-24T22:23:01Z")
I know this is a somewhat old thread but I’d like to chime in. The puzzle states he can’t throw the pieces across. Instead, assuming the bridge is short enough, he could strip naked, tie up his shoes, clothing, wallet, keys, and whatever else in his shirt and throw it across. This might reduce his weight enough that he can carry the three gold pieces across. The puzzle doesn’t state the he’s fully clothed but it seems a safe assumption. Or, since he’s a magician he could use his silks and invisible thread to make a kite, attach one or more gold pieces to it, and fly it as he crosses the bridge. Actually he probably wouldn’t even have to attach any gold to it. If it has enough upward force to lift a gold piece then holding onto it as he crosses, with the gold in his pockets, should work. [Previous page](https://boards.straightdope.com/t/magician-crossing-bridge/692335.md?page=1) [Next page](https://boards.straightdope.com/t/magician-crossing-bridge/692335.md?page=3)