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Will this idea launch a projectile? Weapon.

  1. Nov 3, 2011 #1
    I am making a weapon of sorts and am curious if it will work.

    the project consists of two tubes, a smaller one inside a larger one. To the outer tube there is a slingshot attached, the inner one contains a projectile(arrow, spear, BB, rock). the inner tube is drawn outside of the outer tube with the tension on the sling shot. The inner tube is released and stops suddenly at the rear end of the outer tube.

    does the projectile continue outward at the same speed or will it not transfer the energy properly? The projectile is at the back of the inner tube.
  2. jcsd
  3. Nov 3, 2011 #2
    theoretically it could work, but my intuition is that it won't be very effective. The projectile will continue at the speed of the inner tube. Though it might not even make it out due to drag/friction in the tube.
  4. Nov 3, 2011 #3
    Why don't you just launch the projectile with the slingshot? Is there any benefit expected from the inner tube? Or it is just for a nicer design?
  5. Nov 4, 2011 #4
    the barrels offer a multitude of projectile options.
  6. Nov 4, 2011 #5
    This make sense. I don't see any major problem, in principle. It should work. The projectile will continue with the speed it had right before the moving tube stops.
    The outer tube will get some of the momentum of the moving tube, when this last one stops.
  7. Nov 4, 2011 #6
    You ideally want to convert all the potential energy of the slingshot into kinetic energy of the projectile. By using your inner tube to accelerate the projectile, the potential energy is distributed between the tube and the projectile. They both end up at the same velocity prior to the inner tube hitting it's end stop, therefore the proportion of energy in the projectile will be (projectile mass)/(projectile+tube mass). Unless the mass of the tube is negligible compared to the mass of the projectile you will be wasting a lot of energy and will have a slow projectile as a result.

    The inner tube doesn't give you any advantage that I can see and only serves to make your slingshot ineffective. You want to minimise the mass of the moving parts in your weapon.
  8. Nov 4, 2011 #7


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    If you want to use a tube to direct the projectile then why not use a slotted tube with the rubber band outside and a slider, pushing the projectile via the slot? That way you wouldn't waste energy in accelerating the inner tube.
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