How To Use Science To Answer: “Should You Walk Or Run In The Rain?”

When you are caught off guard, should you walk or run in the rain? I was four or five years old when this question first crossed my mind. I realized that whenever I moved faster through the rain, I felt like the rain was getting heavier. If you’ve ever biked in the rain, you would be able to relate to this feeling.

When I was around ten years old, I was walking home with a bunch of kids after play. It started to pour down suddenly, and we were all caught off guard. We were about 1 Kilometre from a shelter and made a run for it. As we were running, we came across another bunch of kids who were a bit older than us. One of them smirked and said the following:

“If you run in the rain, you only get wet faster. You might as well walk and arrive less wet.”

This incident made a mark on me, and I realized that my own experience hinted at what the bigger kid was saying back then. But I never really tried to figure out the true answer. Until recently! Believe it or not, I came across a research paper that analyses this very situation (details in the references section at the end of the article). In this article, I’ll attack the problem by solving two basic puzzles. Then, we will put the two puzzles together in the end to answer our main question.

This essay is supported by Generatebg

Defining the Problem

Let us say that you suddenly encounter rain and do not have access to an umbrella or a raincoat. The nearest shelter is 500 metres away. You are in a dilemma as to run or walk. You essentially do not know which option would enable you to get less wet.

In order to analyse this situation, let’s make a few unrealistic, yet reasonable assumptions. Firstly, let us assume that the rate of rainfall is constant. In reality, we know that this is not the case, but to get an objective and quick answer, it helps to make this assumption. Secondly, let’s split the effect of rainfall into two components: vertical water exposure and horizontal water exposure.

Whether you run or walk (or just stand) in the rain, you will experience water falling from above. This essentially constitutes vertical water exposure. If you move in the rain (run or walk), you will be exposed to water in the horizontal direction as well. This constitutes horizontal water exposure.

Now that we have sufficiently defined the problem at hand, let us proceed with solving the puzzles.

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Puzzle 1: Vertical Water Exposure

The first trick is to simplify your human body into a generic geometric shape. It just turns out that a three-dimensional parallelogram is well suited for this purpose. A 3D parallelogram is known as a Parallelopiped.

Let us now consider 2 types of parallelopipeds — a straight one and an angled one.

The key point to note here is that regardless of whether we tilt the parallelopiped or keep it straight, its volume remains the same. What this means is that regardless of your direction of motion, your body would receive the same amount of rainfall from vertical water exposure as long as the exposure time is the same.

In short, the only factor that can change the amount of water you receive via vertical water exposure is time. This result will come in handy later on.

Puzzle 2: Horizontal Water Exposure

As far as horizontal water exposure is concerned, the faster you move, the more water you collect. However, the principle of the parallelopiped holds here as well. As long as your start point and finish point are defined, the volume of water between these two points remains the same regardless of your speed.

Sure, the faster you move, the faster you will collect this volume of water. But the volume does not increase. Imagine that your goal is to fill a container up with 1 Litre of water. You can fill it up faster by increasing the water flow, but in the end, you will still end up with the same 1 Litre of water.

The key takeaway here is that the only factor that can change the amount of water you receive via horizontal water exposure is the distance to shelter.

Now that we have solved the two requisite puzzles, we can proceed to answering our main question.

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Should You Walk or Run in the Rain?

So far, we have established the following facts by solving the two puzzles.

1. The amount of water collected vertically increases as the time of exposure increases.

2. The amount of water collected horizontally increases as the distance to shelter increases.

From our problem definition, we know that the distance to the shelter is fixed at 500 metres. This means that the amount of water collected horizontally will remain constant.

Consequently, if our goal is to reduce to the amount of water we collect from the rain, then we should aim to minimize vertical water exposure, i.e., the time of exposure. The only way to minimize the time of exposure is to move faster.

So, the answer to our question is: You should RUN!

What I have done here is just a basic analysis of this problem. If you wish to go into a bit more detail and reduce the number of assumptions, you can check out the research paper I’ve linked below.

To those of you who are just happy to have finally gotten an answer to this pesky question, I hope you start practicing running under wet conditions. All the best!

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Reference: Whether or not to run in the rain — Franco Bocci (research paper).

Credit: Henry Reich.

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Further reading that might interest you: How To Tell A Real Law From A Fake One? and Why Do You See Mirrors Flipping Words?