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B Effects of wind on a moving person

  1. Sep 3, 2016 #1
    Hi,
    I am curious as to the effects of wind on a moving person. If a person is walking at 4 mph and they encounter a 10 mph headwind, would the person feel the wind about the same as if he/she is standing still and is facing a 14 mph headwind? Likewise, if a person is running at 7 mph and encounters a 20 mph tail wind, should the wind feel about the same as a 13 mph tail wind if this person were standing still? I'm guessing there may be other factors that could complicate the calculations, but I'm wondering if these simple calculations could be approximately correct.

    Also, is there a way to approximate how a cross wind would feel to a moving person?

    Thanks
     
  2. jcsd
  3. Sep 3, 2016 #2

    Grinkle

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    Yes.

    If the wind is at right angles to the person's movement, the magnitude of the push is exactly the speed of the wind.
     
  4. Sep 3, 2016 #3

    anorlunda

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    The answers to headwinds and tailwinds are yes. I'm a sailor, and I experience those feelings every time I go sailing.

    Most dramatic. If your boat moves forward at 5 knots, with a 5 knot tail wind, you experience zero wind. If the tail wind was 10 knots, then you feel the wind passing you from behind.

    Yes you do feel cross winds, but I don't know how to interpret your question. But there is a thing called apparent wind, which is the wind you feel based on the combination of your motion and the wind speed and direction.

    xy.php?image=http%3A%2F%2Fwww.nauticed.org%2Fblog%2Fwp-content%2Fuploads%2F2009%2F02%2Ftrue-wind.jpg
     
  5. Sep 3, 2016 #4

    A.T.

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    No it isn't.
     
  6. Sep 3, 2016 #5

    FactChecker

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    You should do the vector calculation and work with the relative wind. This is the "True wind" described above by @anorlunda .

    CORRECTION: The relative wind is the "Apparent wind" described above by @anorlunda .
     
    Last edited: Sep 3, 2016
  7. Sep 3, 2016 #6
    Thanks everyone. The apparent wind was what I meant by cross winds, and I found out how to calculate the speed for that.
     
  8. Sep 4, 2016 #7

    Grinkle

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    Ooops. I was thinking about a treadmill or a person on a sidewalk that is pushed by the wind but not actually having their course altered by the wind when I said that.
     
  9. Sep 4, 2016 #8

    A.T.

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    That's irrelevant, your statement would still be wrong. Draw a vector diagram for the situation like the ones above.
     
  10. Sep 4, 2016 #9

    Grinkle

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    Not sure what I'm missing. Below is meant to be a back or front view of me walking on a treadmill with a fan at 90 degrees to the treadmill. The reaction force that keeps me from sliding off the treadmill sideways seems to me independent of what speed the treadmill is set to, and only dependent on the fan power.

    upload_2016-9-4_10-51-53.png
     
  11. Sep 4, 2016 #10

    A.T.

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    Try a top down view, with all the velocity vectors. And what does a treadmill have do with all this? Just have someone walk on the sidewalk.
     
    Last edited: Sep 4, 2016
  12. Sep 4, 2016 #11

    anorlunda

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    The vector diagrams in #3 apply to you as much as to a boat. They also apply if the magnitude of true wind is zero.

    Remember, your speed is the direction your body moves, not the way your nose is pointing. You can rotate your body to any angle relative to your motion.
     
  13. Sep 4, 2016 #12

    Grinkle

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    A treadmill generates no headwind in still air, so its easier for me to visualize all of the forces.

    If I am standing still, its even easier to picture, or even easier to overlook whatever I am overlooking.

    If I am standing still and a fan turns on to my right, I am pushed to the left by whatever force the fan wind is hitting me with.

    Now, if a second fan is turned on directly ahead of me, I can't see how that changes the force that is pushing me to the left. They are perpendicular to each other.

    If I start walking forward towards the fan in front of me, I increase the headwind force but I still can't see how I am changing the cross-wind force with my motion that is perpendicular to the cross wind.

    I will draw some more diagrams and keep thinking about it.
     
  14. Sep 4, 2016 #13

    Grinkle

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    This is why my intuition tells me a situation involving static forces in one direction is different that a situation where motion is not constrained in any direction. That is what I meant when I said

    Are they not different?
     
  15. Sep 4, 2016 #14

    A.T.

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    Boats aren't running on treadmills. It's not about what is easier for you, but what is right.
     
  16. Sep 4, 2016 #15

    Grinkle

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    The OP wasn't asking about a boat. The question was -

     
  17. Sep 4, 2016 #16

    anorlunda

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    The same vector diagrams work for a boat, a person, an airplane, or any object.
     
  18. Sep 4, 2016 #17

    A.T.

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    And where is a treadmill in that question?
     
  19. Sep 4, 2016 #18

    Grinkle

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    Certainly. I am either very dense or failing to communicate well or both.

    If a boat drops anchor, the boat speed goes to zero and the apparent wind becomes equal to the true wind. Is that not the case?

    If that is the case, then a person walking on a sidewalk is anchored in the axis perpendicular to the sidewalk, is my thinking.

    If that is not the case, then I am really confused.
     
  20. Sep 4, 2016 #19

    Grinkle

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    I agree, no treadmill. I tried to remove that from my thinking.

     
  21. Sep 4, 2016 #20

    A.T.

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    A moving person is equivalent to a boat at rest? Sorry, you don't make any sense to me.
     
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