Half a croissant, on a plate, with a sign in front of it saying '50c'
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Ballistic Bridge

No visible means of support
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A bridge across a canyon is formed of two arches, one for each direction of traffic. The arches are formed of a continuous chain loop roadway, fired in a ballistic parabola from each bank ( a bit like water from a hose) by big motors which cog onto the side of the roadway segments. The roadway is captured by a heavy anchorage on the far side. Cars drive onto and off of conveyors which takes them onto the moving chain loop roadway. No means of support is required for the roadway, the speed it is "fired" at takes account of self weight, traffic weight and wind loads. Yee-haaaah!
Harry Mudd, Jun 25 2007

Apron Feeder http://www.krupp.com.au/images/43.jpg
Here's what an apron feeder looks like [gardnertoo, Jun 30 2007]

[link]






       Still a heavy landing on the other side though...
hippo, Jun 25 2007
  

       fatal flaw--what happens the day the big motors stop running?
The vision of it is rather cool, though.
xandram, Jun 25 2007
  

       So, not a way of settling disputes over the card-table, then. Hmf.
MaxwellBuchanan, Jun 25 2007
  

       Similar to the Evil Knievel Highway, but with a lower survival rate.
ldischler, Jun 25 2007
  

       I think your parabola is going to have to change to another shape. Or the road will tear apart.   

       A series of independent objects, all travelling one after another in a ballistic parabola, are going to be closer together at the top of the parabola than they are at the bottom/ends.   

       A road would be compressing and stretching as it went over the parabola, or, more likely, assume some other shape--I dunno what.
baconbrain, Jun 25 2007
  

       // series of independent objects...// that (and the following sentence) was a very elegant piece of thinking.
MaxwellBuchanan, Jun 25 2007
  

       // going to have to change shape //   

       Neglecting gravity, I suspect the chain would adopt a circular curve - you could imagine the "rest" of the chain being "whirled" underground and this being the top segment of it above ground. So, the shape would tend towards a circle segment, but distorted by gravity and any point or wind loads. Don't ask me what that shape would be(!) Also, if the roadway was a static mat-on-wheels on top of the chain then there would be no "yee-ha" effect - cars could drive across at any speed. The big motor would never stop; there would be sufficient small motors such that to lose up to 2/3 of them would not matter, there would be sufficient reserve of power. Motors would be changed out in this way. Oops, it's all starting to bake...
Harry Mudd, Jun 26 2007
  

       //Neglecting gravity,// Great start to a half-bakery paragraph!
pertinax, Jun 27 2007
  

       If you had a complete circle which also ran through a tunnel (with lots of wheels in it) beneath the canyon, you could rotate it at a speed sufficient to counteract the weight of it. You could either let the cars roll directly on to the fast moving wheel 'o near-certain death and let them experience zero-g as they crest the ridge, or put a stationary arch with bearings on top of it.   

       Actually, you could also give thrillseekers the option of taking the tunnel.
marklar, Jun 27 2007
  

       [Harry] - If thrown objects always travel in a parabola, why would this (essentially an infinite amount of thrown objects connected by infinitely small links) be any different?
wagster, Jun 27 2007
  

       Depends on how you tension your chain. I imagine this as a continuous loop of chain (like an apron feeder with flights upon which you drive: think tracks on an excavator or tank, but wide enough to form a road). The drive rollers and sprockets would be housed at either side, with the high-tension side being the bottom of the loop. Get the speed high enough and the weighty chain will form a loop overhead across which you drive.   

       However if you can tension it high enough to form this loop, then why not just string a suspension apan across the gap and save some power.   

       The other possible arrangement would be to skip the bottom loop, and simply "fire" linked chain across the gap, making a large banked horizontal loop at either end, making a (big) continuous loop with a road in either direction.   

       oh, btw. [marked-for-deletion] bad science. As an operator and maintainer of a couple of large apron feeders where I work, I can tell you with a high degree of certainty that we don't have any materials available that could withstand the stresses, and more importantly, the wear involved. And before you suggest it, magic bloody carbon-nanotubes won't cut the mustard either.
Custardguts, Jun 28 2007
  

       <tries to imagine what an "apron feeder" looks like>
wagster, Jun 29 2007
  

       I'm not sure why you need the roadway. If it's travelling in a free parabola, then anything sitting on it is going to be in freefall (ie, following the same ballistic trajectory), so the road becomes redundant. Just fire the vehicles from an on-ramp to a distance off-ramp.
MaxwellBuchanan, Jun 29 2007
  

       <wagster> No need to try to imagine, see linky above.   

       <custardguts> Is the lip on each "tread" the apron? Otherwise it just looks like a heavy duty conveyor belt.   

       You'ld have to spin this thing to mind boggling speeds to get it to resist gravity and form a self supporting arch, I would think.
gardnertoo, Jun 30 2007
  

       //parabola//   

       A freely thrown object will have constant horizontal velocity (assuming no air friction, as does the comment that the shape is a parabola), but the chain will have constant velocity down the length of the chain for certain, which gives different horizontal velocities at different points. I think that the shape is likely to be a modified catenary (same as a hanging rope), which is not a parabola. I say 'modified', because a hanging rope shape is due to the constant force of gravity in the vertical direction, but the ballistic chain force in the vertical direction is a function of the inertial effect of the chain being forced to follow a curved path. This force is more radial than vertical, and I suppose the resolution of that force in the vertical direction is not likely to be constant at all parts of the chain.
Ling, Jun 30 2007
  

       Thanks Ling, that's a pretty good explanation.   

       And thanks to [gardnertoo] as well, now I can let go of the image of the cookie monster with the tail of an apron hanging out of the corner of his mouth.
wagster, Jun 30 2007
  

       Ridiculous and dangerous? Par for the course. [+]
shapu, Jul 01 2007
  

       [admin: I appreciate Custardguts' experience and contribution, and I agree that this is unlikely to work, but I don't think it quite rises to the level of bad science, so I'm letting the idea stay, more as an interesting gedankenexperiment than anything else.]
jutta, Jul 13 2007
  

       No worries, [Jutta], just taking life too seriously, as I usually do...   

       BTW what a pissant, tiny little apron feeder.   

       Never seen one that clean, though.
Custardguts, Jul 15 2007
  
      
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