Why Does Running in the Rain Get You More Wet?

[fattydq]

If you stand motionless under an umbrella in a rainstorm where the drops fall vertically, you remain relatively dry. However, if you start running, the rain begins to hit your legs even if they remain under the umbrella. Why?Now I know the answer, it's because when you run horizontally, your legs hit the drops that are currently at your knees because they're moving perfectly vertically. But I don't know how to put this into physics terms, it just seems like common sense to me?

Is it just the vectors will meet, since one is pointing horizontally and another vertically, and they will meet at the same place?

 

[tiny-tim]

hI fattydq!

it's all about relative velocity …

draw a vector triangle ​

 

[tomcue]

Yes, you are correct. The reason why the rain hits your legs when you start running is because of the vector addition of your horizontal velocity and the vertical velocity of the raindrops. When you are standing still, the only velocity acting on the raindrops is their vertical velocity due to gravity, so they fall straight down. However, when you start running, your horizontal velocity adds to the vertical velocity of the raindrops, causing them to hit your legs even though they are still falling vertically. This is known as the vector addition of velocities.