Optimal Speed for Transversing Rain: Why?

[Himal kharel]

drops are falling vertically in a steady rain. In order to got through the rain from one place to another in such a way so as to encounter the least number of raindrops, should you move with greatest possible speed, the least possible speed or some intermediate speed? AND WHY?

 

[mathman]

Go as fast as possible. The main factor is how much time you're in the rain.

 

[BobG]

Run!

There's two components to getting wet.

1) How many raindrops hit the top of you.

2) How many raindrops hit the front of you (because you're running into them).

#2 stays constant. The faster you run, the more raindrops hit you from the front per second, but the fewer seconds you're exposed to them.

#1 depends solely upon how long you're exposed to raindrops hitting you from above, so you minimize the amount of rain that hits the top of you by running.

On the other hand, the number of rain drops you run into depends on how fast they're falling. Fast falling raindrops will mean you'll be hit by more on the top of you and fewer on the front of you. Since the surface area of the front of you is a lot greater than the surface area on the top of you, even walking when the rain is falling the fastest is better than running when the rain is falling the slowest.

Of course, waiting for the rain to change speeds probably isn't a viable strategy in most cases. You're stuck with whatever the weather happens to be. But it does put into perspective just how little it matters whether you run or walk.

Toss in some wind and everything changes. Here's a calculator to help you plan your strategy.

http://www.dctech.com/physics/features/0600.php

 

[Drakkith]

Thanks for the link Bob! My first calculations were telling me the faster I go the less rain I get hit with.

 

[BobG]

Thanks for the link Bob! My first calculations were telling me the faster I go the less rain I get hit with.

Provided there's no wind. If you have a 2 m/s wind coming from behind you (about 4 mph), then you'll actually get hit with less rain by walking than by running (once again, a person has a lot more surface area in their front and back than they do on their top).

 

[marcusl]

You might be interested in an earlier thread that discussed this topic (to death...)

https://www.physicsforums.com/showthread.php?t=204749"