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Name: T Lai
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Question:
While in a car when it is raining, why does the windshield get wetter when you are driving than when you stop (like at a stoplight)? We noticed this because at a stoplight, we have to turn off the windshield wipers or it would make a squeaky noise. Is not the rain coming down everywhere at the same time so that you would get the same amount of rain on the windshield? Oh another thing: Is it true that you get wetter when you run in the rain then if you were to walk in the rain?



Replies:
You can imagine how, when moving along a horizontal surface, you will pass more road signs than if you are standing still. The faster you travel, the more road signs you will pass (until a friendly policeman stops you, that is). With the raindrops, your body or a car at rest will encounter a given number of drops. Move your body or the car horizontally through a rainstorm and you will encounter more drops, thereby making yourself wetter. There is naturally a variety of precipitation speeds in a storm, that is, in a storm the rains falls at different rates. You therefore might experience less "wetting" than you might expect when traveling, just because the storm is made that way. But, given a theoretical "set-speed" storm, the faster you move through the storm the more raindrops you will encounter.

An interesting footnote is, that, above a given speed, you might actually become LESS wet, as the wind and vacuum created by your super-fast travel might cause less drops to actually be able to contact your car/plane/jet surface. I do not have the figures available for how fast this would have to be, you might ask the question in the physics section.

Rickru


You might actually get wetter running than you would walking since your body exudes more moisture when you are more active. I can get perfectly drenched when running on a hot day even if it is not raining.

Mortis


Assuming no wind and the rain coming straight down, the only explanation for the windshield getting wetter while driving would be that spray from the tires of other cars is hitting the windshield in addition to the rain when the car is moving. Even if it stops raining, spray from the wet road will cause you to need the wipers sometimes. In answer to the second question, again assuming no wind and rain coming straight down, your body tends to lean forward when running, but is more upright when walking. Thus more of your body's surface area is exposed to the rain when running. But if you are running, you get inside quicker and are exposed to the rain for a shorter time period.

Allsopp



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