How To Avoid Getting Soaked In The Rain Without An Umbrella

7 responses to “How To Avoid Getting Soaked In The Rain Without An Umbrella”

1. 

   spiderlama

   April 19, 2011

   I see one thing wrong with his work: women are NOT always right! lol

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2. 

   Johann

   April 19, 2011

   I’m sure when I did this analysis at uni that it turned out that if walking in the same direction as the prevailing wind, then you should go at the same speed (so your relative velocity is zero). Only if gong against the wind should you go as fast as possible.

   After working it out it turned out that an old wive’s tale already had the answer:

   When caught in the rain without mac,
   Walk at the pace of the wind at your back,
   If the wind’s in your face,
   Then the ideal pace,
   Is as fast as your legs can make track.

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3. 

   Paul

   April 19, 2011

   They looked at this on mythbusters as well. Over a series of trials they found the opposite, that you get more wet when you run. From memory I think they suggested it was because the water penetrates your clothes more when you run. Although, I guess if you are leaning all the way forwards it would minimise this.

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4. 

   Sam Cook

   April 19, 2011

   While not MIT professors, this has already been tackled by the Mythbusters team, who concluded (after a series of practical tests) that you do in fact get wetter if you move faster. They’re method was simple, weigh the dry clothes they were to wear, walk/jog/run through a water-volume controlled rain maker, then reweigh the clothes again. The difference in weight was the mass of the water collected. They found that running caused more water to collect on the front of your body, while walking leaves surface area (ie your head and shoulders, versus your chest and torso) for the rain to be absorbed into the material.

   On a simpler scale, next time you’re driving in the rain, compare the volume of water hitting your windscreen while driving at 60km/h, versus how much collects on the windscreen while stopped at lights – you’ll notice a big difference.

   Maybe there IS a particular technique involved in Lewin’s argument, but we ain’t all Usain Bolt – and I’m not going to be sprinting in the rain leaning forward at 30 degree angle.

   In having said all that lot, there are way too many variables for any of this to have any significant impact on how wet you’re going to be. Best you take an umbrella if it looks like rain.

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5. 

   mkl

   April 19, 2011

   I was always unhappy with the Mythbusters answer. IIRC, it largely concluded that the extra volume came from water hitting the top of your legs as you extend them to run (or walk faster). eg. The surface area exposed to the falling rain. Which made me wonder about a long stride vs a short stride.

   It also didn’t factor in wind at all, which Johann apparently has, so thanks for that contribution.

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6. 

   lol

   April 19, 2011

   Wow all this time wasted calculating how wet we get, just RUN DAMN IT ! No one is gonna lean all the way forward like a mad scientist and run… lol

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7. 

   Kais Gzara

   July 22, 2011

   I am not very impressed by the way the solution was laid down.
   Parts of it are overly complicated for no reason.
   The cos(alpha)x√(+) boild down to Vrain.
   The sin(alpha)x√(+) boild down to Vpm.
   This is obvious when you write the rate of water crossing a surface, in vector form S.(Vrain-Vpm) x rho, where the “.” stands for scalar product of vectors.
   For the head, Sh is a vertical vector, so Sh.Vpm is zero.
   For the front of the body, Sf is horizontal, so Sf.Vrain is zero.
   Very simply, the general formula for the water soaking Peter and Mary, in vector form, is:
   rho x {(Sh+Sf).(Vrain-Vpm)} where the surface vectors are “oriented inwards”.
   We can also “rotate” Sh and Sv to account for the angle of the body of Peter and Mary, to allow for the case(s) where they are not walking upright.
   Although not clearly stated in the video, you have to be careful with the formulas when the rain is already falling at an angle !! Because you may fool yourself thinking, just looking at the formulas, that you can “outrun” the rain, or said otherwise, that rain cannot come out of your body !! Therefore more accurate to express the rate of soaking, as:
   rho x {Max(0,Sh.(Vrain-Vpm))+Max(0,Sf.(Vrain-Vpm))+Max(0,Sb.(Vrain-Vpm))}
   where the Sb stands for the surface vector of the back of the Peter and Mary.
   absolute value.
   Because, Sb=(-Sf), in vector form, this is restated, by saying that, if your front does not get soaked, then your back does.
   An alternative expression to the above, could therefore be:
   rho x {Max(0,Sh.(Vrain-Vpm))+|Sf.(Vrain-Vpm)|}
   where the signs “||” stand for “absolute value”.
   of course, you have to multiply rate by time, for total amount of water soaked, and so you have to multiply the expression shown above, by (distance “D” divided by velocity “Vpm”).
   The final expression is:
   rho x {Max(0,Sh.(Vrain-Vpm))+|Sf.(Vrain-Vpm)|} x (D/Vpm).
   As stated above, Peter and Mary position in the rain, is accounted for, via rotation of the vectors Sh and Sf.
   Soaked water, can then be minimized as a function of walking speed in the rain (Vpm), and inclined position in the rain.

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