Running in the rain

buddyholly9999

I recently saw an episode of mythbusters where they tested the theory that if you run in the rain you get less wet. Their results turned out to be the exact opposite, they found that running in the rain actually made you more wetter. I'm wondering now, taking into account only the "falling" rain (that is to say, not the water getting on you from you splashing the water beneath your feet, etc.), would something like what was proven also be true for sun rays, for example? At noon with full sunlight, would you take in more amount of sun rays if you ran than if you just walk? We, of course, here would have to say that the system of sun rays would not be a full distributed system, and would have to mimic the fall of rain. I use sun rays as just an example, any other example would suffice.

rkkane

that would be true if you could run at the speed of light

Mattara

Remember that the people Adam and Jamie (the Mythbusters) had gotten the result in the other way around.

buddyholly9999

Umm...so did you read the post? That's just one example, perhaps you could think of an example that I'm talking about that might be a little more feasible then. I'm trying to say, is what they proved in mythbusters...something that can be explained in a more general way? Such as the random distribution of rain hitting a certain surface area at an angle MORE THAN LIKELY going to produce more wetness on that surface area if it's moving at faster speeds, kind of thing. Except I don't want to limit the question only to rain.

Dmitri

It actually depends on a direction of rain. If a direction is straight downwards then obviously by running you would collect more water than standing still. Since if you are running you would collect not only rain drops that are falling from above but also the once in front of you.

buddyholly9999

I don't know whether to cry...or to laugh.

Doc Al

The results would depend on what they took as a normal walking speed versus a normal running speed. Obviously, if you walk slowly enough you can get as wet as you wish.

buddyholly9999

Avg. walking speed 3 mph
Avg. running speed 9 mph
distance: .25 mile

now calculate, monkey, CALCULATE!

Doc Al

The monkeys have spoken. Check it out:
http://www.dctech.com/physics/features/0500.php
http://www.dctech.com/physics/features/0600.php

Gokul43201

Their results are wrong, at least in the case where the rain is falling straight down. Of course, I'm imposing the constraint that the distance to be covered is fixed...else there really isn't much sense in the experiment.

GOD__AM

I disagree, consider what happens to your car winshield when it's raining. At a stop if the rain is moderate you can still see, at least more clearly then when moving foward at speed.

Same thing happens to a person. Moving foward at increased speed increases the ammount of raindrops that hit you on the side in the direction of travel. Also these raindrops have a much greater chance of spreading out and wetting a larger area compared to moving at less speed where the drops may be partly deflected by clothing (or skin), and more of that drop hits the ground than absorbing into the clothes from the foward momentum pushing against the drop, and spreading it out.

Also consider that when walking the head and shoulders take the most water, partially shielding the body underneath. Moving foward (espically at a faster speed) increases the area exposed to the rain.

Try running with an umbrella over your head, and I bet you get wetter than walking. Running also causes the arms and legs to travel a greater distance exposing, again, more area to the rain.

redspectacle

Ok. Without getting into formulas or philosophy, why is it that people run in the rain? To get out of the rain. To get under a roof of some kind. So, is speed the real factor here? No. Time is the factor. If you run in the rain to avoid getting wet but you stay in the rain as long as your counterpart who's walking, then what the heck is the point? Observable reality dictates you might get as wet as your counterpart in one trial and less in another. If however you and a buddy are standing a fixed distance, say 100 feet from a roof and it starts to rain and you run 50 feet a second, your exposed to rain for only two seconds. Your buddy waddles along at 1 foot a second and is thus rained on for a minute and forty seconds. I think it is safe to say given all concievable variables, you buddy will always be wetter when he finally arrives under roof. Anyone care to expound or refute?

Gokul43201

This is neither a logical argument, nor a physical one. It is not logical because I didn't say that the rate of rain drop impact reduces with speed. It is not physical, because visibility is not a function of the rate alone but also such things as the splash pattern.

The argument here is not how many drops hit you per second, but how do you minimize the total number of drops that hit you if you have to go from A to B.

Gokul43201

This is the scenario that is being discussed. And it's not entirely obvious that the faster runner gets less wet, unless you do the math (nor is it true under all circumstances). Try the applet in Doc Al's second link.

BobG

The idea that running would get you wetter because you've increased the surface area that's exposed to the rain must assume that all of the water is immediately absorbed and can't move from one place on your body to another.

In reality, as soon as your head and shoulders are saturated, the rain will run down your body getting the rest of you wet, as well.

With no hat or umbrella, the amount of rain does depend both on the time you're exposed to the umbrella and the rate that rain is hitting you. The rate increases as the amount of area exposed to the rain is increased. Speeding up has less and less effect, since it's also increasing the the rate that rain hits you, but going faster never increases the amount of rain that hits you.

With a wide brimmed hat or umbrella, you could assume rain hitting from directly above you would not get you wet, meaning walking under an umbrella would keep you driest.

Edit: Okay, I was wrong. If you vary the angle of the rain and the wind is coming from your back, there is a point where you can get wetter by running faster. In fact, if you run 150 mph the same direction the wind is blowing in a Cat 4 hurricane, you'll be running the same speed as the rain drops, which will be flying nearly horizontal. In effect, you've reduced the rate that the rain is hitting you and very few rain drops will hit you. You can also run too slow. You need to run about the same speed as the wind.

That was a pretty cool web site and using some extreme examples really makes it easy to see what's happening.

DaveC426913

Yes, I have done this experiment myself.

I walked a measured distance of 1 mile at 3 miles per hour in the direct sun and then measured my temp.
I then ran the same distance in the sun at 10 miles per hour (increasing my relativistic velocity by 4.5x10^9%) and then measured my temp again.

For such a tiny increase in relativistic speed, the temperature increase was remarkable! It could be quite plainly concluded that even a slight change in incident angle of EM radiation has a geometric effect on conversion to heat.

BobG

I think the more relevant measure would be whether you get sunburned quicker while running than you do while walking and comparing that to how much exposure you would get running versus walking.

You need to do your experiments about a year apart. If you get a tan during the first part of your experiment, it will give you a false result in the second part of your experiment.