20

Let's assume there's a reason to stay dry from rain. You've a form of a basecamp which can keep you dry.

Is it better to walk or to run back through the rain?

The crux (imho!):

  • Running reduces the time spent in rain
  • Walking reduces the amount of drops you "run against"

There may apply other reasons, too! Just share them. I just wanted to give an idea what the question is all about naming these two points.

Additional considerations may be:

  • (...) what we care about is not the number of drops that hit us, it's our ability to maintain our body temperature (...)

  • I have seen (and had) many 'accidents' from running in the rain

  • Running may attract wildlife
  • 5
    As a practical matter, what we care about is not the number of drops that hit us, it's our ability to maintain our body temperature. When you run, you generate more body heat. – Ben Crowell Dec 8 '15 at 15:23
  • 3
    Bring a raincoat. – gerrit Dec 8 '15 at 16:11
  • 2
    assuming there is a continuous function of speed that gives how much rain you receive per distance, we can intuitively understand that when speed tends to 0, the amount of water received tends to infinity. So run. – njzk2 Dec 8 '15 at 16:25
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    Fantastic question with excellent outdoor applications! +1! – studiohack Dec 9 '15 at 1:02
  • 2
    same question on another stack exchange. virtually identical in the root question. skeptics.stackexchange.com/questions/9903/… – n00b Dec 9 '15 at 20:26
7

It depends on the amount of rain and on the surface you are running/walking on. Now, there is unquestionably a threshold where the amount of rain makes the time exposure factor so significant that running wins without any doubt. However for lighter rain there might be another factor that turns the result.

I remember reading a news paper article about running versus walking in the rain with text from NTB (and as far as I remember the experiment was conducted by NTB itself as well) maybe 10-20 years ago, where the conclusion was that walking made you least wet, based on weighing the clothes before and after the experiment. Unfortunately I am unable to find any references to it now.

Searching for it, I found many references to mathematical calculations like for instance here, which presents the assumptions for the calculations

There are, as you pointed out, two sources of wetness - the rain that runs into you (on your head and shoulders), and the rain that you run into (on your front).

and this is not correct, there is also a third source of wetness - water thrown from the ground with you shoes. And for this factor running is much worse than walking, which also was the conclusion from the NTB experiment. Of course running in urban areas where the rain does not penetrate the ground is much worse than running on grass for instance.

So for heavy rain running is best (ignoring the risk of falling), for lighter rain it depends and walking might be the best option. The fourth source of wetness, sweat, I do not think is very significant compared to the other three.

24

You should run

There's a good video from MinutePhysics that explains it all:

https://www.youtube.com/watch?v=3MqYE2UuN24

The short(er) version is that the amount of water you "run into" depends only on the distance, which is equal whether you run or walk. But the water falling on top of your head depends on how long you stay in the rain, and you can minimize it by running faster.

Also, like Ben Crowell said, the usual motivation for staying dry is to maintain our body temperature. In which case, running is also a better choice since we generate more body heat.

  • In a study I saw (can't remember where), it explained that if you were a large person, any benefit gained from running was lost by 'catching' more water as you ran. – Prinsig Dec 9 '15 at 12:20
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    @Prinsig Well if you do remember where you saw it, please share it. It would be interesting to see how it compares to what's explained in the video. – Roflo Dec 9 '15 at 14:13
  • @Prinsig I think a simple thought experiment suffices: somebody not moving at all would catch an infinite amount of rain. Somebody running infinitely fast would catch a finite amount. So different speeds fall somewhere between the two. – ithisa Dec 10 '15 at 3:37
21

You should walk. I have seen (and had) many 'accidents' from running in the rain - who hasn't?

Although in theory running will keep you drier, there are more important things that staying dry. Running for the sake of staying drier is often done with little thought to the surroundings and potential consequences. You become goal focused - telling you subconscious "Stay dry". Things like paths, rocks and stairs that are likely slippery just don't get noticed.

  • 4
    IMO this is by far the correct answer. Mathy puzzles about raindrops are fun, slipping because things are wet when it rains is not. – djechlin Dec 9 '15 at 4:45
  • “I have seen (and had) many 'accidents' from running in the rain - who hasn't?” me me me! It totally depends on how muddy and steep your trail is. I don’t even have trail running shoes because I don’t mind the reduced traction. You still have to be careful about roots and rocks of course. – Michael Dec 9 '15 at 10:44
17

Theoretically, run. Practically, slowly jog or briskly walk so that you don't slip and fall.

The TV series MythBusters initially tested this with artificial rain and found that walking was better due to less surface area in the rain. However, after revisiting in actual rain, they found that running was better.

Also, Lifehacker summed it up nicely:

the less time you spend in the rain, the better

And for complete nerdiness, they have a formula:

Total wetness = (wetness per second X time spent in rain) + (wetness per meter X meters traveled)

Edit: Updated to include more practical advice, as many have pointed out that running in wet terrain can be dangerous. However, I don't think anyone will interpret this advice as "run as fast as you can".

  • 5
    The best way to avoid slipping and falling is to not run. – djechlin Dec 9 '15 at 4:45
  • Wanted to give the same answer, I saw that episode years ago. Funny stuff :) – Wills Dec 9 '15 at 22:16
8

It also depends on your type of clothes. Wearing "non breathable" clothes will get you more sweaty than the rain will get you wet sometimes. Also if you wear a coat but no rainproof trousers, than running will probably get your trousers more wet, because of surface area increase. I think the best tactic can be seen by observing people in rain:

  • Those travelling a short distance in very heavy rain with few clothes run.
  • Those travelling long distance with waterproof equipment in mild rain walk.
6

Having spent a lot of time running and walking in the rain I can say from experience that it's very much an individual specific choice.

Personally I like to keep my body temperature up as I find it difficult to do so whilst walking; so I have to run. I'm reasonably fit so can run for an hour if need be, but others might not be, and for them it could be dangerous to run for 20 minutes and be very hot and then suffer from the cold for 40 minutes. There are also those people who don't feel the cold and can maintain a high body temperature without doing much movement (think about those with high metabolic rate), for those people walking would be best.

So, to summarise you would need to assess your own physical body and make a judgement call based on that and your best estimate as to how long it would take you to get back to base camp. Also, clothing is critical (are u wearing breathable waterproofs with insulated layers, or a t-shirt)!

Other environmental factors (high wind, extremes of temp, fog etc) should be considered but I'm not sure if that helps answer your question!

3

If you assume that both methods are about as effective, Then another parameter comes into place: If it rains very little it might be worth running, before it starts to rain more. If it rains alot, then you might want to maximize the possibility of if clearing up, i.e. walk slowly. (Or just wait in cover)

protected by Rory Alsop Dec 9 '15 at 23:09

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