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Rubber bouncing balls

  1. Jul 20, 2008 #1
    Is it possible to have many rubber bouncing balls (7?) and send it into orbit?
  2. jcsd
  3. Jul 20, 2008 #2


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    Hi Bright Wang! :smile:
    Too cryptic :confused: … explain! :smile:
  4. Jul 20, 2008 #3
    I think he is talking about that demonstration of momentum where you have several bouncing balls on top of each other, let them fall and then watch the top one bounce up very high. The question then is, is it possible with enough balls/starting height to have the top ball reach escape velocity.

    I would imagine that it is possible, considering that adding another ball to the top should make it go faster after the whole thing hits the ground. But still, it would be interesting to work it out to see how many balls you need and so on. I'll give it a try later today.
  5. Jul 20, 2008 #4
    No. I'm not sure where that rumor started, but I do know how.

    You are likely referring to the event of, say, a tennis ball placed on top of a basketball, and when they are both dropped in unison the tennis ball shoots upward at a much greater speed and height than if dropped by itself.

    There are many variations of this, with one being a "physics toy" consisting of larger plastic sphere with 2 or more smaller spheres. The largest, bottom sphere has a vertical rod attached, and the increasingly lesser diameter(and mass) top spheres have a hole through them which allows them to move along the rod.

    Under ideal conditions, a seven-stage device who's smaller spheres are 1/2 the diameter and mass of each preceding one will multiply the potential reaction speed such to double it for each stage(but the force cut in half!), due to how the initial "shock wave" is altered during transmission through the next sphere.

    So, if the whole 7-stage assembly hits the hard surface at 1mph, the leading edge of the shock wave in the next smaller sphere will be 2mph, then 4, then 8, then 16, then 32, and finally 64mph.

    That's far short of 17,500 mph.

    So, let's drop it at 10 mph. Stage 7 would be 640 mph.

    Now, drop it(or mechanically impact) at 100 mph. The 7th stage would idealize at 6,400mph.

    Sounds somewhat promising? No.

    Even at the above last example, the shock wave would destroy the arrangement, possibly even with the first stage, and certainly by the 4th or 5th stage. So its usefulness for acceleration has definite PRACTICAL limits.

    Anyway, it's a very interesting effect indeed, and NASA is studying a variant of this, but for the opposite reasons... the ultimate shock absorber.
  6. Jul 20, 2008 #5
    lol hmm I heard it from my physics teacher... and he says 7 should do it...
  7. Jul 20, 2008 #6
    7 will not do it, or 12, or 127, or whatever number of stages.
    What material can withstand a shock wave of 17,500mph?

    None that I know of. The closest I'm aware of is a titanium disk that had a military shaped-charge behind it and expelled at a little more than 7,000 mph.

    Edit: the disk did not stay as a disk, it resembles an empty bullet shell.
    Last edited: Jul 20, 2008
  8. Jul 21, 2008 #7


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    Since your physics teacher is not here to defend him/herself, I will take that with a grain of salt. It should be easy to see, from conservation of energy, that no matter how many balls you drop, or in what configuration, they cannot bounce any higher than their initial height.
  9. Jul 21, 2008 #8
    :wink: Hint: what does conservation of energy say if not all of the balls bounce back up?
  10. Jul 21, 2008 #9


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    Yeah, this is an odd thing to say. The whole point of the device is to concentrate the potential energy from the first 6 balls into the 7th. 6 stay on the ground but the 7th sure can go a lot higher than where you dropped it from!
  11. Jul 21, 2008 #10


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    This is misleading. No single ball takes a hit of 17,500mph.
  12. Jul 21, 2008 #11
    Your right, as far below that point, severe fragmentation would likely occur, destroying any real likelyhood for the end 17,500mph result.

    However, the mathematics do point to it's potential with respect to the effect of "speed-doubling" when each next sphere is in direct contact and also 1/2 the diameter and mass of the previous sphere.

    Let's look in reverse, ignoring all other bastard factors, just to make a "picture" of potentiallity:

    17,500/2= 8,750

    8,750/2= 4,375

    4,375/2= 2,187.5

    2,187.5/2= 1,093.75

    1,093.75/2= 546.875

    546.875/2= 273.4735

    273.4735/2= 136.719

    136.719/2= 68.36

    68.36/2= 31.48mph

    With the largest mass sphere impacted at 31.48mph, the following spheres will transform the leading-edge of the shock wave to double the speed and half the force each time.

    The above 10-stage device will theoretcially eject the last sphere at 17,500mph, but the force on that sphere will be 512x LESS than the force of original impact with the first sphere.

    So, the first sphere might as well be a bowling ball, with the last being a B-B.

    Even still, I think the shock wave would destroy, or even "lock" furtherance in the system beyond the 5-6th stage due to interial aspects.
  13. Jul 21, 2008 #12
    aww too bad.... I was looking forward on trying it...
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