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Newton's cradle-gun

Shoots ball bearings using the power of gravity
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Inspired by [baconbrain]'s comment on the Passive Rail Gun idea about the bearings moving "downhill", you drop a ball bearing, guided by a pipe, maybe at a slight angle off vertical. At the bottom of the straight pipe there's a semicircular track so the ball bearing curves around until it's moving up instead of down. Then there's another straight section of pipe. This one has a stack of ball bearings in it (the bottom one can be supported by a wire ring). The moving ball bearing hits the bottom of the stack and stops, transferring its momentum and kinetic energy to the ball at the top of the stack (which also has more potential energy). At the top of the stack, there's a semicircular track to direct the ball back down again, to roughly where it started. At this point you can have another downwards track parallel to the first, (where it loses potential energy and gains kinetic energy) then another semicircle at the bottom, then another upwards stack of magnets (where the top ball gets the kinetic energy from the moving ball, and also has more potential energy), etc, forming a coil-like structure (but with straight sections)

Then at the end the ball comes out with as much speed as if it had been dropped from the height of all the stacks off balls put together. 5 coils with 1 meter stacks should be the equivalent of dropping a ball 5 metres, which would make it move at 10 metres/second. 500 coils should get you 100 m/s

There's another design I thought of but haven't fully worked out which extracts potential energy from the whole stack of balls, instead of just the top one: instead of having multiple coils, there's just one loop, and the second ball follows the same path as the first ball. The first ball might need to get out of the way so it doesn't interfere with later ones. Also the final ball just smashes into the wire stack support ring instead of leaving the device. If this second one still isn't enough power, you can add multiple coils again, so long as the last coil loops back into the first. I calculate that with 100 ball bearings in a 1 metre stack (average height in stack being 50cm) each loop should be equivalent to dropping a ball 50 metres, which gets you about 30m/s speed. With 100 coils of this it's like dropping something 5 kilometres, which may be enough to break the device or reach 300 m/s (nearly the speed of sound). Though it couldn't go faster than the ball's terminal velocity. Hopefully it would explode or something before terminal velocity.

caspian, Aug 21 2010

Stokes' Law http://en.wikipedia.../wiki/Stokes%27_law
Relevant [8th of 7, Aug 21 2010]

*cough*freelunch*cough cough http://www.cheapsti...57/free_meal_on_yo/
[Voice, Aug 21 2010]

Galilean cannon https://en.wikipedi...iki/Galilean_cannon
from the title I assumed your idea would be something like a Galilean cannon [xaviergisz, Aug 22 2010, last modified May 07 2016]

[link]






       um...what?   

       [Marked-For-Tagline] //hopefully it would explode or something//
Grogster, Aug 21 2010
  

       I said what?
baconbrain, Aug 21 2010
  

       (registification)
vertical line of ball bearings magnetically held to the (in)side of a vertical long oval-racetrack on it's side.
  

       manually pop the first one off, up and around the top, and it shoots around to smack the line on the bottom   

       inertia is transmitted to the second one which pops off, goes around the track and smacks the line on the bottom... at twice the speed of the first one...   

       etc.
FlyingToaster, Aug 21 2010
  

       // Hopefully it would explode or something before terminal velocity. //   

       No, it won't.   

       The terminal velocity of a steel sphere of (say) 10mm diameter in your atmosphere is nowhere near enough to make it "explode", although it might get quite hot, maybe enough to soften and eventually melt.   

       Freefall "iron bombs" can be dropped from 10 km AMSL and after they hit the casing is only mildly warm (if they have an inert filling, that is). A ball bearing won't even reach the same terminal velocity as a streamlined projectile, as the ratio of mass to area is cube to square.   

       <link>   

       The principle of energy multiplication by perfectly elastic collisions is valid, (v1 - v2) = - e (u1 - u2) being the governing equation, but for small objects it has to be done in vacuo. And you don't need a "stack" of ball bearings; a suitable pushrod will do.   

       There is no free lunch; you're simply aggregating the potential energy from each ball, which you have raised to a height h when you "load" the system, into the last ball in the sequence. You might as well just drop it a distance n x h (where n is the number of loops, and h is the height though wich each ball descends).   

       [-] for complete failure to recklessly use explosives in a highly dangerouns, inadvisable and possibly illegal manner to propel an unguided piece of metal at lethal veloccities on an unpredictable path.
8th of 7, Aug 21 2010
  

       //There is no free lunch//
Spoiler alert.
AbsintheWithoutLeave, Aug 21 2010
  

       [FlyingToaster] you've got the gist of my second version, which was kind of my favourite for it's more efficient use of potential energy from all the balls. In the first version, the race track coiled around multiple times, more like a multi-storey ca rpark.   

       [8th of 7] I may have used the word "explode" incorrectly, but I was thinking the balls might shatter and fly apart on impact with each other. Steel ball bearings are too strong for that? My apologies. Maybe I need neodymium magnets after all.   

       The other thing was I thought the track may get ripped apart when the ball's in the curved part.   

       //you're simply aggregating the potential energy from each ball// agreed.   

       // You might as well just drop it a distance n x h //   

       My method will be at least as slow, but more compact. It may be easier to aim too.   

       Suggestions of devices to drop a ball from a great height are welcome.   

       //And you don't need a "stack" of ball bearings; a suitable pushrod will do.//   

       Interesting. If the ball hits something of larger mass, it will bounce off and not transfer all its energy. I had thought it had to hit something of exactly equal mass. Thought I suppose a long thin pushrod could be equal mass.   

       //[-] for complete failure to recklessly use explosives in a highly dangerouns, inadvisable and possibly illegal manner to propel an unguided piece of metal at lethal veloccities on an unpredictable path.//   

       Guilty as charged.
caspian, Aug 22 2010
  

       Finally limited by speed of sound in steel, I suppose, but more likely limited to when the energy loss due to each collision equals potential energy in each stage.
Ling, Aug 22 2010
  

       I'm having trouble visualizing your idea caspian.   

       My version of a Newton's Cradle weapon would be a line of closely spaced suspended steel balls of progressively smaller diameter. Give the large ball at the end a whack and it transfers its energy to the next ball and so on. The last and smallest ball in the line would be loosely held, so when hit by the penultimate (second smallest) ball, would shoot out. This is probably well known variation of a Galilean cannon (though I can't find it).
xaviergisz, Aug 22 2010
  

       you wouldn't even need the track except the curvy bit at the bottom: just let the balls fly higher and higher into the air with each successive collision: Newton's Cradle Recursive Mortar
FlyingToaster, Aug 22 2010
  

       What are the magnets for? Until the magnets came into it, it was an agreeably daft way of accumulating gravitational potential energy, but now I'm confused.
pertinax, Aug 23 2010
  

       The magnets don't really belong in the idea, I just suggested them as something more brittle than steel, so there's something to smash. The Passive Rail Gun had magnets, which I'd removed when I replaced magnetic force with gravity to get this idea.
caspian, Aug 23 2010
  

       Perpetual motion machines violate the first two Laws of Thermodynamics:   

       1) The, You can't get something for nothing Law - (Conservation of Energy), and...   

       2) The, Not only can you not get something for nothing, you can't even break even Law - (Entropy)   

       So, how does this violate them? I don't know, but my guess is on the up-ramp. In order to transfer momentum (V * m) from the bottom of the stack to the top, the 'force' through the string of balls must be fighting the acceleration of gravity the whole way. Imagine the up-stack a million balls high; would the top ball pop off? Not likely...   

       Really clever idea, though [=]
Wily Peyote, Aug 23 2010
  

       Ya know... if the objective is to shoot the last ball, then all the other ones can be tethered, like the original cradle... save using a friction-laden track.   

       //[-] for complete failure to recklessly use explosives in a highly dangerouns, inadvisable and possibly illegal manner to propel an unguided piece of metal at lethal veloccities on an unpredictable path.//   

       little round grenades should work just as well as little round ball bearings.
FlyingToaster, Aug 23 2010
  

       Have to agree with [Wiley], the energy to push all the balls is not free. I have a sneaking suspicion that even under unrealistic ideal conditions, enough energy will be lost at each impact to equal the gain in height between the lower and upper balls.
MechE, Aug 23 2010
  

       while various forces may conspire against the contraption: air and track friction, rotational inertia (as a ball bearing starts to roll on the track) and momentum transfer losses from hitting the balls, the idea's valid as far as gravity: use thereof, is concerned.
FlyingToaster, Aug 23 2010
  

       // little round grenades should work just as well as little round ball bearings //   

       That;s the sort of talk we want to hear, [FT].
8th of 7, Aug 23 2010
  
      
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