Physicist Reveals Why You Should Run in The Rain (sciencealert.com)
- Reference: 0175305921
- News link: https://science.slashdot.org/story/24/10/23/0150203/physicist-reveals-why-you-should-run-in-the-rain
- Source link: https://www.sciencealert.com/a-physicist-reveals-why-you-should-run-in-the-rain
> ... Let p represent the number of drops per unit volume, and let a denote their vertical velocity. We'll denote Sh as the horizontal surface area of the individual (e.g., the head and shoulders) and Sv as the vertical surface area (e.g., the body). When you're standing still, the rain only falls on the horizontal surface, Sh. This is the amount of water you'll receive on these areas. Even if the rain falls vertically, from the perspective of a walker moving at speed v, it appears to fall obliquely, with the angle of the drops' trajectory depending on your speed. During a time period T, a raindrop travels a distance of aT. Therefore, all raindrops within a shorter distance will reach the surface: these are the drops inside a cylinder with a base of Sh and a height of aT, which gives:
> p.Sh.a.T.
>
> As we have seen, as we move forward, the drops appear to be animated by an oblique velocity that results from the composition of velocity a and velocity v. The number of drops reaching Sh remains unchanged, since velocity v is horizontal and therefore parallel to Sh. However, the number of drops reaching surface Sv -- which was previously zero when the walker was stationary -- has now increased. This is equal to the number of drops contained within a horizontal cylinder with a base area of Sv and a length of v.T. This length represents the horizontal distance the drops travel during this time interval. In total, the walker receives a number of drops given by the expression:
> p.(Sh.a + Sv.v). T
>
> Now we need to take into account the time interval during which the walker is exposed to the rain. If you're covering a distance d at constant speed v, the time you spend walking is d/v. Plugging this into the equation, the total amount of water you encounter is:
> p.(Sh.a + Sv.v). d/v = p.(Sh.a/v + Sv). d
This equation proves that the faster you move, the less water hits your head and shoulders, but the amount of water hitting the vertical part of your body remains constant. To stay drier, it's best to move quickly and lean forward. However, you'll have to increase your speed to offset the exposed surface area caused by leaning.
[1] https://www.sciencealert.com/a-physicist-reveals-why-you-should-run-in-the-rain
Or to put it another way (Score:2)
The quicker you reach shelter the drier you'll be. If you stay out in the rain it doesn't matter how you move you'll get just as wet, it'll just be on a different part of your body.
Clothing (Score:3)
> The quicker you reach shelter the drier you'll be. If you stay out in the rain it doesn't matter how you move you'll get just as wet, it'll just be on a different part of your body.
And to be pedantic, note that *you* are water proof, it's your clothes that sop up the water.
Your body is well suited to being in the rain. Remove your clothes and it doesn't matter how wet you get, once you get out of the rain you'll dry very quickly.
Then you can put your clothes back on.
(This post is made in the spirit of all the other posts, such as "use an umbrella", currently in this thread :-)
Re: (Score:2)
> And to be pedantic, note that *you* are water proof
That is my favorite thing to remind people of when it's wet outside. Oh, don't worry about me. My skin is waterproof!
Did they factor in the chance of slipping? (Score:3)
If you run it's more likely you'll slip and get full-blown wet. That's not factored in, so, back to your equations, Dr Treiner...
The MBA factor. (Score:2)
> If you run it's more likely you'll slip and get full-blown wet. That's not factored in, so, back to your equations, Dr Treiner...
We've just been given a running recommendation, from an expert who understands everything, and yet nothing.
Hell. I’ve never seen a finer example of an MBAs actual value.
*$350/hr. golf clap*
TL;DR - This.
Re: (Score:2)
> If you run it's more likely you'll slip and get full-blown wet. That's not factored in, so, back to your equations, Dr Treiner...
If it's raining hard enough that you need to run, you're going to get full blown wet no matter what, you're running in order to spend less time in the rain. Where the fuck is my research grant money?
Re: (Score:2)
Im a runner: If its not raining, and its hot, you get wet no matter what from sweat. If its cold, not raining, and you wearing 2 layers, you get wet from sweat. Almost all conditions, you wet. Running in the rain in warm weather, assuming its light so you dont get blinded by the rain, is the same.
Re: (Score:2)
> you're running in order to spend less time in the rain.
This is really the only answer that anyone needs. Presuming that the rain is constant enough, the amount of water falling on the person is a function of exposure time. Running at around 6 miles an hour will result in being out in the rain half the time that walking at around 3 miles and hour will.
Re: (Score:1)
The Ministry of Falling Down approves this message.
Superman... (Score:2)
You fly in a superman orientation infinitely fast. Then the only raindrops that hit you are those that were blocking your route.
For light rain it's possible to dodge the raindrops completely.
For heavy rain and a sufficient distance it's best to go vertically until you're above the clouds.
Re: (Score:2)
According to the article:
> The water hitting the vertical part of your body stays the same regardless of speed
That intuitively seems false, but I can't figure out the math (the notation is weird, which doesn't help). I read the article several times, and I don't understand the logic of this physicist. The organization of the article is horrific. For example, this sentence:
> Let p represent the number of drops per unit volume
What is "unit volume?" Volume of what? The only other use of the word "unit" in the entire article is unit of time!
Re: (Score:2)
'Per unit volume' is used all the time in cases where the exact unit doesn't matter, other than it being volumetric. 15,000 raindrops per cubic meter, 120 raindrops per cup, etc. Outside of my field, I think the most I've ever seen that term used is to define density: "Mass per unit volume".
As far as the first point goes: Try envisioning a horizontal rectangle with a constant amount of dots in it, where the dots move downward from the top at a constant rate at a random point along the x-axis, with a bar swe
Re: (Score:2)
> Try envisioning a horizontal rectangle with a constant amount of dots in it, where the dots move downward from the top at a constant rate at a random point along the x-axis, with a bar sweeping across the rectangle. Over repeated trials, the bar will touch the same amount of dots regardless of how fast it sweeps across the rectangle, but the odds of a dot spawning right on the bar (rain landing on your head) is decreased at higher speeds.
That doesn't sound right. Regardless of speed, the bar's top always occupies the same proportion of the horizontal space.
Re: (Score:2)
> According to the article:
>> The water hitting the vertical part of your body stays the same regardless of speed
> That intuitively seems false, but I can't figure out the math (the notation is weird, which doesn't help). I read the article several times, and I don't understand the logic of this physicist. The organization of the article is horrific. For example, this sentence:
Agreed. I had started a reply cause I thought it was making sense, but I was reading that as "the water hitting the _HORIZONTAL_ part of your body", and I thought it just needed a timespan qualification, like:
"The (amount of) water hitting the (horizontal) part of your body stays the same (over a given period of time) regardless of speed"
But that's not what they're saying. And it makes zero sense to me that the water hitting the vertical part of your body would remain the same regardless of speed. This can
Re: Superman... (Score:2)
Or fly around the planet in the opposite direction of earth's rotation at the speed of light, until you turn back time just enough to before you left your house. This time don't forget your umbrella.
Mytbusters did this one (Score:4, Informative)
They came to the opposite conclusion but they were [1]test IRL [youtu.be] and not just theorizing.
[1] https://youtu.be/HtbJbi6Sswg?t=20
Re: (Score:2)
It was mostly due to splashing, which wet the lower half of their bodies. The devil is in the details when it comes to models.
Re: (Score:2)
Theorizing has the benefit of being backed by some specific formulas that describe a system. If Mythbusters ever used a scientific method they'd probably bust that too. There are many "myths" they "busted" which were none the less actually facts not myths. You need to remember they are an entertainment show, not very scientific.
My favourite one was the experiment that assumed that a boat had the same forces applied to it by water as by air and called the myth busted despite there being photographic evidence
Paper (Score:2)
My uncle and his friends wrote a sorta-joke paper about this in college, but it was a serious analysis with a few experiments thrown in.
His findings were similar to the MythBusters, it didn't really make a difference if you were running or walking. He didn't take into account leaning, though.
As for his bona fides, he has a doctorate in physics with a specialty in thermodynamics.
MythBusters would like a word (Score:3)
MythBusters did [1]this very experiment [youtube.com] a while back. According to their experiment, running increases the amount of rain falling on you compared to walking.
[1] https://www.youtube.com/watch?v=a2axIxq0QM4
Re: (Score:2)
is this per fixed time, or per fixed distance ?
Re: (Score:2)
Right. If its fixed time it won't make any difference, for fixed distance it would.
Re: MythBusters would like a word (Score:2)
Well, if there is a hurricane and the flood water is over your head, then you wonâ(TM)t get any wetter, no matter how you move.
Re: (Score:2)
And that experience didn't list any edge cases, didn't control for angle, didn't control for splashing, etc. etc. etc. Mythbusters is nice and entertaining but if they ever saw a scientific method they'd probably bust that too.
Next up (Score:2)
Some research on running with scissors.
Of course, the form you have to sign to participate is a bit longer ...
once while riding a motorcycle (Score:3)
it started raining, you know what rain feels like at 65 mph? it feels like being poked with lots & lots of needles, when i got home i was chilled to the bone, pulled into the garage and pulled the door shut, stripped naked water poured out of my boots, my clothes were dripping and made a puddle i had to sweep out the door, then i went straight to a hot shower and hot bowl of soup afterwards,
Re: (Score:2)
But that's exactly one of the points: The amount of water hitting you in the front stays the same for the distance. If you travel faster, you will encounter more front splash per time. If you are not moving at all, you encounter infinitely little front splash, but it takes infinitely long to get out of the rain.
So, all that matters is the rain dropping on head and shoulders, and this one you can minimize by reducing the amount of time out in the rain.
Re: (Score:2)
A good fairing is one of the most underrated features of a motorcycle. Almost no reviews even talk about their efficacy....
Rules (Score:2)
This is veering into Rule 34 territory, especially the part about the soup :)
He got it all wrong... (Score:2)
... one should not run in the rain. Years of scientific research have proven so many times already that one should DANCE IN THE RAIN! :-D
Re: (Score:2)
[1]I hope you dance [youtube.com], but [2]some of us Walk in the Rain [youtube.com]
[1] https://www.youtube.com/watch?v=RV-Z1YwaOiw
[2] https://www.youtube.com/watch?v=Y1mi8Usy1zA
Re: (Score:3)
Don't forget to sing. You'll be happy again.
Terrible science (Score:2)
What about the drops of water splashing back up off the ground which will increase when you start walking/running?
Someone kill the blurb's author (Score:2)
> Physicist Reveals HOW You Should Run in The Rain
HOW you should run in the rain. Not WHY. What sort of raving incompontent produces this drivel and... .oh, wait. This is one of those AI blurbs isn't it.
Journalism, and communication, is dead. This is our dystopian future.
no use (Score:3)
no use to complain,
when you're caught out in the rain,
your mother's quite insane.
cat food, cat food, cat food, again?
Re: (Score:2)
If the rain comes, they run and hide their heads
They might as well be dead
If the rain comes
If the rain comes
Usually that's when (Score:2)
I run in the rain like an idiot and wind up breaking my ass. Then I'm really wet. I prefer umbrellas.
Seems incorrect (Score:3)
This doesn't seem to account for the horizontal velocity of the rain and it includes the false statement "When you're standing still, the rain only falls on the horizontal surface".
Generally speaking, rain and wind are highly correlated because the atmospheric conditions that lead to rain are also involved in the creation of wind. Although it is possible for rain to fall straight down, it's not a valid assumption to say that it will fall straight down.
doh. (Score:1)
ah man, now I need to go and apologise to my brother, he told me this when were like 8 or 7, I laughed at him. Damn science!
Peer reviewed? (Score:2)
Was this peer reviewed?
Until then I will continue to use an umbrella to stay drier in the rain.
Minute Physics explaination (Score:2)
[1]https://www.youtube.com/watch?... [youtube.com]
[1] https://www.youtube.com/watch?v=3MqYE2UuN24
Subject line should mention staying dry (Score:1)
Here I thought I was reading about rain somehow creating less wind resistance or better for your body, etc. only to find out it's an article about staying dry.
Unconvinced by the reasoning... (Score:2)
I'd have thought that the volume you pass through remains constant. Assuming constant rainfall, the amount of water in this volume is also constant and you collect all of it. Thus the Sv component shouldn't change. The faster you move the less rain from above so faster is better for the Sh part.
My car windshield proves. (Score:2)
This is bullshit math.
But I wasn't really paying attention because I was unfolding an umbrella.
Slushie (Score:2)
> To stay drier, it's best to move quickly and lean forward. However, you'll have to increase your speed to offset the exposed surface area caused by leaning.
Skipping that this contradicts the statement preceding it, where forward movement just shifts the raindrop hits to the front of your body from the top, while the total number of hits remains constant, when I read the headline, I thought this was going to be a physiological argument where the rain kept you cooler, so you could exercise harder and longer, like drinking a slushie into your gut during a marathon.
I prefer the second opinion (Score:2)
In the documentary featuring Gene Kelly, and what he recommended
Re: (Score:2)
If you sing really load you can maybe blow away the wind.
Seriously? (Score:2)
This was a homework question in my first-year physics course in 1976.
This ain't "news".
Until you bust (Score:2)
So, you might get less wet but then you bust your tail ;P
Unstated Optimization Goal (Score:1)
There are 2 things that the computations are neglecting: 1) wind and 2) that one may prefer to have 1 side of the body relatively dry.
1) Wind will cause 1 side of the vertical surface to be impacted by more water droplets than the other.
Depending on which way one is facing and the velocity of the wind, it is possible that 1 side remains dry at the expense of the opposite side.
2) I generally don't mind if my back gets wet, because it will often be placed next to the back of a chair/seat minimizing the effect
Mythbusters (Score:1)
They weighed a jumpsuit after walking and running through simulated rain. Came to the opposite conclusion.
Re: (Score:1)
I remember watching that. I also remember that being one of the least scientific-method-y tests that they ever did. I was immediately skeptical then, and remain now.
Missing from the analysis? (Score:2)
I suspect that both the speed and the direction of any wind that's blowing render the analysis in TFA invalid.
Assuming (Score:1)
a spherical cow
I once cycled home through the rain so fast.. (Score:2)
I didn't even get wet. Honnist.
Already studied this (Score:2)
I had a physics class where we had to do this analysis.
But wait, there's more (Score:2)
The excellent newsletter of the Danish engineer's union "IngeniÃren" worked on this problem a while back, though for bikers. Turns out when you move fast enough, you also get an "air envelope" that pushes done of the drops that would otherwise have hit you out of the way.
Re: But wait, there's more (Score:2)
That should be "some of the drops", of course.
Stay under cover... (Score:2)
... until the rain stops.
Runaway... (Score:2)
Del Shannon thinks you should be [1]walking in the rain [youtube.com].
[1] https://www.youtube.com/watch?v=wSWMJxbxj7c
Umbrella (Score:5, Informative)
Use an umbrella. Duh.
Re: Umbrella (Score:2)
Simpler explanation: In the limit, standing still forever is the worst and moving instantaneously is best. The optimum movement is somewhere in between.
Re: (Score:2)
I might characterize "somewhere in between" as "what will actually happen"... rather than "optimum", which'd be -- as you point out -- moving instantaneously. Well heck, as long as I'm being pedantic :) maybe the very worst would be walking exactly under the rain cloud as it moves forever. Or instantaneously running into the nearest ocean.
Re: (Score:1)
But my umbrella always inverts when I run in the rain!
Re: Umbrella (Score:2)
Too fast - You should move as fast as possible, but no faster!
Re: (Score:3)
That's why I leave a decoy umbrella behind on the sidewalk, so the rain hits it instead of me.
You're holding it wrong. (Score:2)
But my umbrella always inverts when I run in the rain!
You're holding it wrong.
Angle it against the wind.
Re: (Score:2)
> Use an umbrella. Duh.
The physicist is correct about running to decrease the amount of attracted water. He also mentioned that running faster is better. However, he left out the most important part, which is that running at the speed of light will minimize the water. Of course, that's silly. What's interesting is how fast one has to run to approach zero water.
Then again, running in the rain maximizes splashing water on one's shoes and pants, so that's worse.
We need to ask for Randall Munroe's thoughts on this.
Re: (Score:2)
if you run faster than light (FTL), you travel back in time and go back to the time where is no rain, so problem solved, run FTL
Re: (Score:2)
Or just live in the desert, so that you frolic in wetness whenever you're luck enough to get rain. (Best during the first monsoon of the summer.)