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Not an exact brain teaser, but

  1. Feb 26, 2005 #1
    This was in a maths textbook.

    An arrow approaches its mark, (where its supposed to hit) but as it approaches closer and closer, it will approach half the distance it was at some time ago away from the target, and so on and so on and so on..

    So im asking: Why does the arrow ever reach the target?
     
  2. jcsd
  3. Feb 26, 2005 #2

    Hurkyl

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    Ask yourself this first: why wouldn't the arrow ever reach the target?
     
  4. Feb 26, 2005 #3
    Huh..? confused.. :confused:

    I don't understand what you mean. Forgive me if i am being an idiot of somewhat flavour..

    To answer your question in a ridiculous, ambiguous, and idiotic way: the distance between the arrow is somewhat infinite..?

    I've heard it reaches the target because it depends on dimentions..but i wasn't quite satisfied with that answer, so im asking here..
     
    Last edited: Feb 26, 2005
  5. Feb 26, 2005 #4

    dextercioby

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    The arrow is one object,how do you define:"the distance between the arrow"...?

    What dimensions are involved here...?:confused:

    Daniel.
     
  6. Feb 26, 2005 #5
    I honestly don't know. I've just heard of answers of that kind, but by no means am i saying those are true.
     
  7. Feb 26, 2005 #6

    dextercioby

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    Well,then do some recherche on the problem and then come with a "sound" version to us...:wink:

    Da
     
  8. Feb 26, 2005 #7
    I presume you'll have to see evidence that i've put some effort into it? :wink:

    Fair enough. I will try and reword the question, and put down my 'hypothesis'.
     
  9. Feb 26, 2005 #8

    dextercioby

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    I mean to be stated very clear,just like a maths problem,not to leave room for interpretations or missunderstandings.

    Daniel.
     
  10. Feb 26, 2005 #9
    Space is quantized so eventually it gets to the point where it can't go halfway any more and has to "make the leap"
     
  11. Feb 26, 2005 #10
  12. Feb 26, 2005 #11

    dextercioby

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    Yes,my guess is that is sounds very much like one of them.Anyway,let there be noted,that,up until now,the OP is not clear what he is trying to ask...

    Daniel.
     
  13. Feb 26, 2005 #12
    I didn't know it was Zeno's paradoxes. It was just in my mathematics textbook and interested me a lot.

    Thats the kind of answer i wanted, since (well now i know) the mathematics behind it seems complicated..

    Let me try and make the question more accurate. (although it has already been answered)

    Consider a archer firing his arrow to a target at a certain distance away, E. When he fires the arrow, the arrow will travel towards the target, until it reaches a distance of E/2, then E/4, then E/8 and so on.

    Looking at this, the arrow shouldn't hit the target at all. However, we know this is not true, as we do actually see the arrow hitting the target.

    So, what causes the arrow to hit the target?
     
    Last edited: Feb 26, 2005
  14. Feb 26, 2005 #13

    Curious3141

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    This is an ancient paradox, and one that was not satisfactorily resolved till the theory of limits was formalised.

    Ask yourself :

    Can the sum of an infinite series be finite ? Under what circumstances ?

    What does a constant velocity of the arrow mean ? What is the relationship of the distance travelled to the time taken to travel that distance ?

    Hence what is the time taken to travel each smaller "division" of the distance ? What is the total time taken ?

    I think you can answer your own question here.
     
  15. Feb 26, 2005 #14

    Hurkyl

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    *sigh* There is absolutely no empirical evidence space is quantized. Not only is there no working model of the universe that includes quantized space, none of the popular alternatives (e.g. String Theory and Loop Quantum Gravity) feature quantized space.


    You said the distance is E. Why do you now think it's infinite?

    It is true that you have divided the problem into an infinite number of subtasks, the distance is still finite.
     
  16. Feb 26, 2005 #15
    Forgive my idiocy. I'm not as familiar as you are on QM.

    EDIT: 'infinite' removed.
     
  17. Feb 26, 2005 #16

    Curious3141

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    Forget QM, this has nothing to do with QM (Quantum Mechanics). The poster who talked about spatial quantisation is wrong.

    Just think of it as an infinite series problem. What conclusions can you draw ?
     
  18. Feb 26, 2005 #17
    You can look at this another way too. If you are marking off the milestones then why should it even ever leave the starting point? It is never halfway to anything before it leaves the starting gate.
     
  19. Feb 26, 2005 #18
    Should there be?
     
  20. Feb 26, 2005 #19

    Hurkyl

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    I would presume there should, before one goes off spouting quantized space as if it was a fact.
     
  21. Feb 27, 2005 #20

    GCT

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