# Rain

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1323014.  Thu May 30, 2019 10:04 am

If you get caught in the rain and need to find shelter, do you stay drier by running or walking?

Originally, Mythbusters tested this back in 2003 using artificial rain, and their experiments showed that you stay drier by walking. However, they conducted this study indoors, and when they revisited the question in 2005 using real rain, they came to the opposite conclusion. [1]

This conclusion, that it's better just to run and get out of the rain as fast as you can, is backed up by this 2012 video from MinutePhysics. [2]

A more extensive academic study in 2012 found the answer to be more ambiguous, depending on wind speed/direction and body size/orientation. [3] When speaking qualitatively without taking those factors into account, the general concensus was this:

 Quote: For rain falling vertically, the best strategy is to run as quickly as possible. The same is also true for motion into the wind. For motion downwind, there may be an optimal speed, which equals the component along the direction of motion of the wind velocity. This happens only if the ratio between the cross-section of the body perpendicular to the motion and the horizontal one is large enough; otherwise, the best choice is again to run at the maximum speed one can reach.

The study produced two equations that can be used to calculate the optimal speed to travel to ensure the minimal rain cover – factoring in rain speed, rain density, mass of water, wind speed, speed of the person, surface area of the person, and the angle of the direction they're travelling in relation to the wind direction. Their final conclusions were thus:

 Quote: An optimal speed exists subject to the sole condition that the rain wets the rear face of the surface, irrespective of the intensity of the wind and of [wind direction]. ... Our study of the behaviour of solid bodies in the rain has revealed a wide range of situations, and general rules cannot be found. We can say that the presence of a tailwind seems to be a favourable, but not always a necessary condition for the existence of an optimal speed. In some cases, we have found that the value of [the optimal speed] depends on the drop size, and in other cases it does not.

So that's cleared that up.

 1323016.  Thu May 30, 2019 10:30 am In 2010, researchers in Switzerland were able to accurately measure rainfall by tracking how much the rain interferes with signals produced by mobile phone antennas. The results produced by this method, using telecommunications data supplied by Orange, produced a more accurate and more spacially-representative measurement of rainfall than the traditional measurements taken using rain gauges and radar. https://www.sciencedaily.com/releases/2010/01/100127111110.htm

 1323017.  Thu May 30, 2019 11:12 am I wouldn't say it was more accurate than radar - it IS radar. The mobile phone antenna network forms a multi-static array which can be used for many things. One of them is detecting and localising rainfall, while another is detecting and localising what were previously considered to be "stealthy" aircraft... PDR

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