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Confused about my frisbee (flight dynamics)

  1. Jul 31, 2008 #1
    If I simply drop a stone, it takes s seconds to hit the ground. If I throw the stone parallel to the ground, it also takes s seconds to hit the ground, regardless of horizontal momentum.

    However, if I throw my frisbee it will be airborne for much longer than it does when I drop it, even if I throw it parallel to the ground. In fact, the harder I throw, the longer it stays in the air.

    Why? I would guess that it floats on the air somehow? Or perhaps, when I say that I throw it parallel to the ground, it has just enough upward angle to gain the same amount of lift as gravity is pulling it down, and so they cancel each other until i loose momentum.

    But if that is the case, it leaves the question of how the lift is generated. I've read that you get low pressure on the top of the disk due to the rounded rim (rounded upwards) but would not that simply make MORE of the air go ABOVE the disk, and so make it HIGH pressure compared to below?

    Enlighten me, please!

    k
     
  2. jcsd
  3. Jul 31, 2008 #2

    LURCH

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    You are correct that there is an aerodynamic force acting against gravity. As for how the lift is generated, there are several threads. Search for lift on aircraft wings, and you'll get a ton of hits, many of them filled with contraversy. The key to the expalnation you've aparently heard (about the rounded top), is that the curve makes the air go faster over the top, and faster moving air has lower pressure.
     
  4. Aug 1, 2008 #3

    rcgldr

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    Upward angle is correct. It's the combination of forward speed and effective angle of attack that produces lift. The shape reduces the drag, but even a flat plate (no curve) will fly, and a frisbee thrown upside down with enough speed and angle of attack will glide for a short while, although the flat plate will tend to roll more. A frisbee rolls a little. An aerobie doesn't roll (if properly "tuned"), is much thinner and glides much further than a frisbee.

    http://en.wikipedia.org/wiki/Aerobie

    A somewhat recent thread about lift from an airplane wing.

    https://www.physicsforums.com/showthread.php?t=247336
     
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