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Homework Help: The Physics of Fishing and Rotational Motion

  1. May 11, 2012 #1
    1. The problem statement, all variables and given/known data
    I am writing a large paper on the physics of fishing and would like to know what equation would prove the statement that a longer fishing pole would result in a higher velocity of the lure?

    My physics book gives me a gamut of equations for rotational motion but I can't figure out which on applies to this real world situation.

  2. jcsd
  3. May 12, 2012 #2
    Is the lure being cast? Show us the gamut of equations.
  4. May 12, 2012 #3
    Yes, the lure is being cast. My original equation that I used for my rough draft was: rotational inertia= (1/3)(m)l^2. But that does not prove my statement at all.
  5. May 12, 2012 #4
    You know that the faster the lure is going when the line is released, the greater the distance it goes. So what equations apply to that situation.
  6. May 12, 2012 #5
    That isn't really the situation I need an equation for. I need one that is length dependent. Think of a catapult, I need an equation that would say the longer the arm the greater the velocity of the projectile. Except in this case the arm is the fishing pole and the projectile is a lure.
  7. May 12, 2012 #6
    That's what I'm steering you towards without telling you the answer. The velocity of the lure is rod length dependent. Obviously you require one that defines velocity.
  8. May 13, 2012 #7
    I looked in my physics book and none of them have ω and length. The closest thing is ω=(rotational displacement/time), but that clearly is not it. The other one is L=mvr, but I'm not sure if it would help me. Those two are the closest ones so whatever you're wanting me to find, I don't think is in my book.
  9. May 13, 2012 #8
    How about omega*R, where omega is rotational speed in radians/second and R is the radius? The simple formula gives the velocity at the end of the radius. So if you have a radius of 5 feet and a rotatonal speed of 1 revolution per second the tangential velocity is:

    2*pi*5=10pi feet/sec
  10. May 13, 2012 #9
    Lawrence you're the man, that one was not in my book anywhere. If I have a 7ft pole and am holding it from the very end the whole length of the pole will act as the radius, correct? So r=7ft?
  11. May 13, 2012 #10
    That is correct if you consider the pole doesn't flex during the motion. The length of the pole is the radius.
  12. May 13, 2012 #11
    That's all I need, thanks for the help!
  13. May 14, 2012 #12
    It is not a simple question of pole length. One the one hand we must figure the length, spring rate, and lure mass. One the other hand we must match all that to the skill and casting style of the fisherman, which is not purely rotational. The idea is to apply the greatest possible force over the longest possible distance without breaking the line.
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