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Is it worth running in the rain?

  1. Jun 27, 2012 #1
  2. jcsd
  3. Jun 27, 2012 #2

    jedishrfu

    Staff: Mentor

    personally I prefer singing in the rain.

    with respect to the question though. If you stand still then you'll be taking a shower that lasts the duration of the storm so your cross-section area is your head and shoulders. If you run then your cross-section is the front of your body and the amount of wetness depends on the duration of the storm or how fast you run and how far away the shelter is.

    To solve this problem you first need to decide what worth is. Many runners will tell you its worth it to get the experience especially if you're into marathons. Here's a website that provides tips for running:

    http://www.nydailynews.com/blogs/running_dialogue/2010/09/expert-tips-for-running-in-the.html [Broken]

    If worth is defined as money then standing still you're less likely to fall than running and so wont incur an ER visit. On the other hand standing still you might catch cold or pneumonia based on how cold it is outside or have a higher risk of getting struck by lightning if you're in a thunderstorm or hail if that is present...

    If worth is defined by how heavy you'll be then that depends on what you wear if anything , how much water hits you and how much is retained in your clothing and skin.

    Heuristically speaking, the end result is common sense rules: Run if it just starts raining and slow down if you're getting soaked but get inside as soon as you can and dry off unless you like singing in the rain.
     
    Last edited by a moderator: May 6, 2017
  4. Jun 27, 2012 #3

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    ^^What he said!

    The Mythbusters studied this one, but I recall I found a flaw in their method (I don't think they collected the water-on-head correctly).

    When thought-experimenting, it is useful to exaggerate things, and look at extreme cases:

    If you moved very slowly, to the point that it takes you an hour to move the 100 yards to your door, would you be wetter or dryer than if you sprinted there taking only 10 seconds (I said exaggerate!)?

    I've done this. Sprinting = dryer (my real name is Carl Lewis, by the way).

    However, when walking slowly, the water hits your head and shoulders primarily. If you have a hat, then most of the water comes off with it when you get inside. If you sprint, you need to change your shirt.

    If it is a true downpour, and you have more than 100 yards to go, you're just gonna be wet, so enjoy it.
     
  5. Jun 27, 2012 #4

    D H

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    Staff Emeritus
    Science Advisor

    First off, this article is from 1987. I don't know what you mean by "these days".

    This obviously isn't a burning question in physics research. Physics researchers however aren't the only ones who publish in physics journals. Physics educators also publish. It's very easy to create a bad homework type problem. Creating a problem that is interesting to students, that stresses key points rather than sidebars, and that is neither too easy nor too hard to solve -- that's a hard problem!

    The running in the rain problem is a perennial favorite. It's an interesting problem with which students can identify. It involves multiple concepts such as how to make good simplifying assumptions, how to mathematically formulate and solve equations of motion, and the concept of cross section that is so important in particle physics. This problem can also be modernized by having students develop a simulation, and perhaps even relax some of the not quite realistic simplifying assumptions.

    In short, this is a nice problem for physics educators.
     
  6. Jun 27, 2012 #5
    When I some time ago thought about this, I concluded, assuming rain falls vertically
    and body could be approximated as a parallellepipede:

    1) Rain hitting top of you is proportional to time dwelled in the rain, independent of
    horisontal distance travelled.

    2) Rain hitting front of you is proportional to distance, independent of time passed in
    the rain.

    So it should pay running because it reduces water hitting the top surface of you, but
    doesn´t change water hitting your front. If you could be approximated as an upright
    straight column or something.

    If your body may be approximated as a sphere of cross section A, the water droplets
    uniformly distributed falling at vertical speed Vv and you run the distance S at speed Vh: Then your speed relative to the "cloud of raindrops" is SQRT(Vv^2 + Vh^2) and the time you pass is S / Vh, so the length of "tunnel in cloud" and total amount of water you receive is proportional to SQRT[1 + (Vv / Vh)^2]. So also in that case it pays run. :eek:
     
    Last edited: Jun 27, 2012
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