Physicist Reveals Why You Should Run in The Rain (sciencealert.com) 116
Theoretical Physicist Jacques Treiner, from the University of Paris Cite, explains 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.
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.
Umbrella (Score:5, Informative)
Use an umbrella. Duh.
Re: Umbrella (Score:2)
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But my umbrella always inverts when I run in the rain!
Re: Umbrella (Score:2)
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I sure thought this story would be a rich target for humor, but even that one wasn't modded funny.
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You're holding it wrong. (Score:3)
>> But my umbrella always inverts when I run in the rain!
You're holding it wrong.
Angle it against the wind.
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But my umbrella always inverts when I run in the rain!
You're holding it wrong.
That's only for the iUmbrella ... :-)
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It's an expensive umbrella, maybe I don't want it to get wet!
Re:Umbrella (Score:4, Interesting)
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.
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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
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It also increases the chance of slipping and falling, and getting even more wet as you land on the wet surface you're walking on.
I think just having an umbrella or wearing rain gear will just let you walk normally in the rain and not get wet. And you can take your time in case it's particularly slippery.
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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.)
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Completely different math with an umbrella. I guess you'd be looking for the speed limit where the umbrella is destroyed by the wind or water.
Or to put it another way (Score:2, Flamebait)
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:5, Funny)
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 :-)
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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!
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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.
So I should strip off all my clothes, and run through the rain, while using my umbrella.
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Yep.
I was a paperboy back in the 1960's delivering the evening paper while riding my bike and hurling the rolled-up paper at the subscriber's front door (or dog, if needed).
Anyway, this was a coastal town and it rained fairly often. I discovered that the most comfortable way when raining (whether summer or winter) was to wear shorts and a t-shirt. I put cooking oil on the exposed parts if it was cold so the water rolled right off. That left me feeling mostly dry.
This was way better than being bundled up wit
Did they factor in the chance of slipping? (Score:5, Insightful)
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.
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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?
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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.
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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.
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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!
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'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
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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.
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Over repeated trials, the bar will touch the same amount of dots regardless of how fast it sweeps across the rectangle
This is the entire question, and the author didn't prove it, just assumed it?
I don't see how this can be true.
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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)
Mytbusters did this one (Score:5, Informative)
They came to the opposite conclusion but they were test IRL [youtu.be] and not just theorizing.
Re:Mytbusters did this one (Score:4, Informative)
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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.
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MythBusters would like a word (Score:3)
MythBusters did this very experiment [youtube.com] a while back. According to their experiment, running increases the amount of rain falling on you compared to walking.
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is this per fixed time, or per fixed distance ?
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Right. If its fixed time it won't make any difference, for fixed distance it would.
Re: MythBusters would like a word (Score:2)
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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.
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Mythbusters did teach me that there's nothing cooler than blowing up a cement truck [youtu.be].
Next up (Score:4, Funny)
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:4, Informative)
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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.
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Rules (Score:3)
This is veering into Rule 34 territory, especially the part about the soup :)
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I had to look it up.
Rule 34, Federal Rules of Procedure: Producing Documents, Electronically Stored Information, and Tangible Things, or ... for Inspection and Other Purposes.
I'm not a lawyer, but it sounds to me like it says pictures are required.
He got it all wrong... (Score:2)
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Re:He got it all wrong... (Score:4, Funny)
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.
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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?
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They might as well be dead
If the rain comes
If the rain comes
Usually that's when (Score:2)
Seems incorrect (Score:5, Insightful)
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)
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)
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)
My car windshield proves. (Score:2)
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
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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)
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)
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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.
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I was in the Navy at the time it dropped and multiple people around me stopped running to get out of the rain after watching it.
I'm not sure what the episode said but those people got really fucking wet and despite being relatively drenched, they still felt the need to explain that mythbusters has assured them that my drier clothes were not the result of running.
Trust me man it's on TV.
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.
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 walking in the rain [youtube.com].
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I like this cover of Flash and the Pan
https://www.youtube.com/watch?... [youtube.com]
So you can... (Score:2)
So you can fall on your ass running on wet pavement and said physicist can get a laugh.
Ask Joe (Score:2)
Incorrect (Score:2)
Run in the rain, if you must (Score:2)
But please - don't leave the cake out in it.
Best? Depends on your objective. (Score:2)
I think putting on a raincoat and holding a bag over your head would be better than running without protection. Also, maybe you'd like to NOT risk a slip-and-fall or a collision when you can't maneuver as well as you are used to. There are more things to optimize for than "number of raindrops hitting you". Bu of course this is a physics problem featuring spherical physicists. Fritz Zwicky was right.
What about dancing in the rain? (Score:2)
Visualize it (Score:2)
I imagine a rectangle with a narrow top and a large front . As you move through the rain you rotate it forward so only the top catches the rain.
Only, you can transform this into another problem. Simply a car driving over a large plain . It starts on (x,0) and drives towards the Y axis while keeping a constant velocity in the Y direction.
How should it drive then to minimize the driving distance. Well, the higher the speed in X direction the better.
The amount of rain you catch is now equivalent to the driving
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thinking about it, if your rectangle is not bent forward but always upright, you simply have to calculate the swept area by calculating the cross section of the rectangle perpendicular to direction (Vx,Vy).
Why do I have this picture (Score:2)
Of someone hunched forward running in the rain, as always is the case?
Yay! We figured out what physics now tells us a long time ago.
Already solved (Score:2)
Repost (Score:2)
The same story was covered before by /. sometime near 2001 ±2 years.
The real question (Score:2)