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Does wind help a runner run laps faster?

  1. Aug 6, 2012 #1
    If you are running on a circular/elliptical track, and wind is blowing in one direction, will it have a positive effect?

    I'm thinking the "macro" forces should cancel out. However, when you're running against the wind, I think you'd get some turbulent air currents, whereas when you're running with the wind, it might maintain laminar flow. Based upon this idea, I think the presence of wind would slow you down overall.
     
  2. jcsd
  3. Aug 6, 2012 #2
    The face of your body, with your arms and such, is less aerodynamic than your back is. So, yes, I would imagine it would slow you down overall.
     
    Last edited: Aug 6, 2012
  4. Aug 6, 2012 #3

    A.T.

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    Drag is proportional to flow velocity squared. So if you run upwind and downwind it's best to have no true wind.
     
    Last edited: Aug 6, 2012
  5. Aug 6, 2012 #4

    Danger

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    There's a secondary effect, but I don't know whether or not it falls into the framework of this question.
    Running into a strong wind makes it harder to breathe, which might hamper performance.
     
  6. Aug 6, 2012 #5
    It depends on the orientation of the wind relative to the direction you are running. The drag force is expressed as

    [itex]D = C_D 1/2 \rho v^2 S[/itex]
    Where:
    CD is the drag coefficient
    S is the projected surface area in the direction of the wind velocity (The shadow of the human body with respect to the wind)
    ρ the density of air

    If the wind is in the direction you are running, then you will get an extra boost of momentum.

    More important than the drag force is the power required to overcome the drag. This is proportional to the velocity cubed

    [itex]P_{drag} \approx C_D 1/2 \rho v^3 S[/itex]

    In a 30 second sprint the untrained athlete will have a power output of about 909 watts. Assuming this person is running at 10 mph (4.4 m/s) the power required to overcome drag is on the order of

    [itex]K*85.18 [Watts][/itex]
    where K is the product of the constants mentioned above. You can see that if K is 1 then the power available to for sprinting is reduced by about 9 percent.
     
  7. Aug 6, 2012 #6

    russ_watters

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    A.T. had it correct. Assuming a simple case of a round-trip with two lengths, one with and one against the wind, a wind equal to your running speed doubles the average wind resistance you feel. The leg with the wind has no wind resistance, the leg against it has 4x the wind resistance.

    Also, though power against the wind is a cube function of wind speed, if the wind is moving with respect to the ground, the ground is doing some of the work. That's why its effect on you is only a square function. For example, if you double a car's speed over ground in no wind, there is an 8-fold increase in power required to overcome the drag. If you hold the car's speed steady and add a headwind, the increase is only a factor of 4. This is easier to see if the car is standing still and apply a wind: the car doesn't have to do any work to overcome the wind, the ground does the work.
     
  8. Aug 6, 2012 #7
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