Running in the rain

 Running in the rain

Sometimes I watch people running because it rains, and I wonder why they do it. Simple: if you halve the time you spend in the rain, you must halve the volume of water collected right?

Wrong. Things are not that simple. Today I decided to look how wet does a person gets when walking or running 100 metres under the rain.

How much rain? Let’s say 100mm in the rain gauge for a day. This gives an average of 1.16 millilitres per square meter per second.

How long does it take? About 71 seconds if you walk, 20 seconds if you run. Usain Bolt can do it in 10 seconds.

I gathered all this in a table. Here is a simplified version of it:

Speed	Time to do 100m	Volume of water collected on top of head and shoulders (about 0.1 sqm)	Volume of water collected on face and front of body (about 0.85 sqm)	Total collected
Walking	71 sec.	8.29 ml	10.96 ml	19.24 ml
Jogging	20 sec.	2.32 ml	10.96 ml	13.28 ml
Usain Bolt	10 sec.	1.16 ml	10.96 ml	12.12 ml

Note: this assumes no wind, and rain drops falling speed of 9 m/s.

Conclusion: if you run, you collect less water on your horizontal bits (top of head and shoulders). However, your vertical bits collect more water. And that is absolutely the same amount (10.96 ml) no matter how fast you go.

Morality: the best strategy is to walk with an umbrella. Don’t you love it when science meets common sense!

Reference:

In this article they think that running fast is best!

https://www.scienceabc.com/eyeopeners/stand-still-or-run-in-rain.html#why-is-it-better-to-run-through-the-rain-mathematically