walking or running in the rain

[Bill Brasky]

Originally posted by: CycloWizard
OK, it looks like the relationship for weight gain with time is the following:

dW/dt = D*c*(v_d*a+v_r*b)

Where dW/dt is the rate of weight gain (the rate of getting soaked )
D is the rain 'density' (drops/m^3 or some such)
a is the person's 'thickness' (front to back)
b is the person's height
c is the person's width (shoulder-to-shoulder)
v_d is the rain's falling velocity
v_r is the velocity that the person is moving forward

Integrating gives the right-hand-side multiplied by t, where t is time in the rain and the left-hand-side becomes the total weight change.

W = D*c*(v_d*a+v_r*b)*t

I treated the person as a rectangular prism moving at a constant velocity, along with other standard assumptions you all mentioned above (rain falls straight down, constant density, constant velocities of rain and the person). Just looking at the equation tells me that the rate at which you get wet will always be higher for the person running (since v_r is higher). However, you need to determine the time required to get from place to place to know which will have a larger net wetting effect. I'll throw this in Excel and see how it comes out. It may even be that the answer differs for the fat guy over the tall guy, but if you're tall and fat, you're going to get soaked no matter what.

Edit: It looks like the net weight change is always lower for running. However, the walking skinny guys get as wet as the really fast, running fat guys. There is an asymptote at high velocities for each body type.

A perfect example of why I love this forum. :laugh:

Usually I walk since I'm a firm believer in umbrellas. But without one, running makes the most sense to me.

 

[Oblivionaire]

Originally posted by: SRoode
I'm a big believer in instincts. Since the human instinct is to run in the rain, it's probably the way to go. Millions of years of pre-programming there...

Yes but how do you know that programming isn't the result of being chased by a rhinoceros in the rain? There's nothing more serious than a rhinoceros about to charge your ass. I just put on my robe and wizard hat before walking through the rain.

 

[Fayd]

Originally posted by: Oblivionaire

Originally posted by: SRoode
I'm a big believer in instincts. Since the human instinct is to run in the rain, it's probably the way to go. Millions of years of pre-programming there...

Yes but how do you know that programming isn't the result of being chased by a rhinoceros in the rain? There's nothing more serious than a rhinoceros about to charge your ass. I just put on my robe and wizard hat before walking through the rain.

wide brim on the wizard hat helps in the rain.

 

[travisray2004]

Id have to say TIE, because you will come across the same ammount of rain if your walking as if your running.. but it also depends if you pick your feet up, sometimes you might kick the rain on the back side of your leg, which would mean you woul have more rain water on you if you run. SO, i think its a tie, if you are a sugar cube i suggest you stay away from the rain... I would have to ask the people in Seatle, WA. To see what the true answer is..

 

[MrColin]

Theoretically, I don't think there is a dryness advantage to running versus walking. In reality, I think you are usually better off running because your clothing gets more absorbant the wetter it gets until saturated. Also, you will start drying off sooner if you run, and you wont get as cold.

 

[SuperFungus]

"if you're tall and fat, you're going to get soaked no matter what."

If you're tall and fat do you actually get any wetter, shure more water hits you but that water is spread over a greater surface area as well. If an ant runs accross the parking lot and only gets hit by a single drop of rain he is still completely covered in water, so is he drier than the human who gets hit by, say 20 drops of rain? Something seems flawed here.

 

[CycloWizard]

Originally posted by: SuperFungus
"if you're tall and fat, you're going to get soaked no matter what."

If you're tall and fat do you actually get any wetter, shure more water hits you but that water is spread over a greater surface area as well. If an ant runs accross the parking lot and only gets hit by a single drop of rain he is still completely covered in water, so is he drier than the human who gets hit by, say 20 drops of rain? Something seems flawed here.

Well, it depends on how you define 'wet'. In my model, I assumed that 'wetness' increased with the mass of water that you intersected. You describe what I would call a 'specific wetness', or a wetness per unit area. In my model, the frontal wetness per unit area must always be equal for all people, as will the top wetness per area. The net total wetness per area will still change depending on the shape of the person though, as the water falling from above has a different effect than the water the person runs into.

 

[DrPizza]

Originally posted by: travisray2004
Id have to say TIE, because you will come across the same ammount of rain if your walking as if your running.. but it also depends if you pick your feet up, sometimes you might kick the rain on the back side of your leg, which would mean you woul have more rain water on you if you run. SO, i think its a tie, if you are a sugar cube i suggest you stay away from the rain... I would have to ask the people in Seatle, WA. To see what the true answer is..

That only accounts for a portion of the problem. Don't forget that you have shoulders, a head, etc. Hold a piece of paper horizontally in the rain. It doesn't matter if you walk with it or run with it; (ignoring wind, etc.), it will get wet at the same rate. Thus, the less time it's in the rain, the drier it stays.

Or, and this is simpler to comprehend your error: let's say it's 30 feet to the door and raining pretty hard. You run to the door and get there in 3 seconds. We've all been in that situation before, so it should be fairly familiar. Now, your coworker walks at a steady pace to the door. To keep his pace steady, he walks along side a snail (and snails never deviate from their speed ) It takes him 2 hours to get to the door walking reallllly slowly (but always moving). Yes, they sweep out equal volumes of space. But, we all know the slow moving person is going to end up wetter.

 

[SuperFungus]

What if you ran sideways?

 

[CycloWizard]

Originally posted by: SuperFungus
What if you ran sideways?

Then you'd probably trip, fall, and end up really wet. If you can run just as fast sideways as forwards and you're relatively skinny, then you'd stay drier running sideways.

 

[Peter]

Heading for a dry spot? Run - you'll get there in a MUCH shorter amount of time.

Out in the open? Run - you'll get just as soaking wet, but at least the extra body heat will keep you warm.

 

[Smilin]

Yes you would 'hit' more rain by moving forward fast, but more would miss you as well. Rain that would have fallen harmlessly just a few inches in front of you will now be run into. But rain that would have hit you may now miss by just an inch.

The two would almost cancel each other out. There will be a small net increase in the amount of rain hitting you but it will be minimal. Your speed horizontally relative to the vertical speed of the drops just isn't very much. A fast moving car would be different.

The tiny net increase of rain hitting you each second will be more that offset by the fewer seconds you spend in the rain.

So: running = drier.

Of course the wise man will walk. With an umbrella.

 

[brikis98]

Originally posted by: DrPizza

Originally posted by: travisray2004
Id have to say TIE, because you will come across the same ammount of rain if your walking as if your running.. but it also depends if you pick your feet up, sometimes you might kick the rain on the back side of your leg, which would mean you woul have more rain water on you if you run. SO, i think its a tie, if you are a sugar cube i suggest you stay away from the rain... I would have to ask the people in Seatle, WA. To see what the true answer is..

That only accounts for a portion of the problem. Don't forget that you have shoulders, a head, etc. Hold a piece of paper horizontally in the rain. It doesn't matter if you walk with it or run with it; (ignoring wind, etc.), it will get wet at the same rate. Thus, the less time it's in the rain, the drier it stays.

if by horizontally, you mean the paper is parallel to the ground, then yes, running would obviously be preferable.

however, if you held it vertically and faced the paper into the direction of motion, running may be worse. that's because when standing still, only the thin edge of the paper is exposed to (vertical) rain. as soon as you move, the whole page collides with rain in front of you, so much more surface area is exposed. granted, this is true as you walk as well, but the impact depends on the vertical and horizontal spacing of rain drops.

Originally posted by: DrPizza
Or, and this is simpler to comprehend your error: let's say it's 30 feet to the door and raining pretty hard. You run to the door and get there in 3 seconds. We've all been in that situation before, so it should be fairly familiar. Now, your coworker walks at a steady pace to the door. To keep his pace steady, he walks along side a snail (and snails never deviate from their speed ) It takes him 2 hours to get to the door walking reallllly slowly (but always moving). Yes, they sweep out equal volumes of space. But, we all know the slow moving person is going to end up wetter.

well, obviously, it's not so black and white (or cut & dry, if you will ). 2 hours will obviously worse, but 10 seconds vs. 3 seconds might not be as clear. there is likely some trade off and hence we search for the "optimal" speed.

 

[SuperFungus]

Originally posted by: CycloWizard

Originally posted by: SuperFungus
What if you ran sideways?

Then you'd probably trip, fall, and end up really wet. If you can run just as fast sideways as forwards and you're relatively skinny, then you'd stay drier running sideways.

Thanks for the advice, I'll get practicing then. Pretty soon I'll be making all you people with your "umbrellas" look like complete idiots as I blow by you at a full sideways sprint!

 

[xtknight]

Depends where the rain decides to hit.