# Question: A Car In The Rain

Discussion in 'Earth Science' started by jmpet, May 27, 2009.

1. ### jmpetValued Senior Member

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A car driving in the rain at 60 miles an hour.

Does it get less rain on it, more rain or the same amount of rain if it were standing still?

3. ### James RJust this guy, you know?Staff Member

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If the rain is falling straight down, then the car gets more rain on it when it is driving.

5. ### jmpetValued Senior Member

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Yes, it's falling straight down.

Why more rain?

7. ### chris4355Registered Senior Member

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because asides from some falling straight down on it, the car also drives into falling water drops in front of it.

8. ### baftan*******Valued Senior Member

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Same rain. It doesn't matter if it is moving or stationary. It is under the rain. The time matters though. If you stay more under the shower you get more water.

9. ### James RJust this guy, you know?Staff Member

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Because the car now presents a larger surface area to catch the rain. Not only does the rain fall on the roof from directly above - it now also hits the front of the car.

10. ### baftan*******Valued Senior Member

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Car doesn't present larger area when it is moving than it is stationary. Same surface, same rainfall...

11. ### James RJust this guy, you know?Staff Member

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But I just explained that it does, baftan.

12. ### baftan*******Valued Senior Member

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You explained your assumption. Where is the evidence? Why should I or someone else accept that car has a larger surface depending on angle of rain or movement? Imagine same rain (with an angle or directly downfalling does not matter) hitting a car
a) while car is moving
b) while car is stationary

and you are telling me rain catching changes. If this was the case, car manufacture engineers should have considered that the surface area of their cars would change when it is moving. Is that so.
If you are telling me that car is catching the rain before it falls to the ground, please consider the fact that the same car is escaped from the rain behind. So your car has a fixed surface and it covers the same surface on the ground and under the rain. Time makes difference: 5 minutes some rain, 1 hour more rain.

Last edited: May 27, 2009
13. ### mardRegistered Member

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Some surfaces of the car will catch more rain but some will catch less rain. It is feesible that some cars will have a smaller surface area exposed to the rain when moving at 60mph than when stationary.

The car will still get hit by more rain however, because the car catches up with more rain than it leaves behind. It would take a peculiarly shaped car to catch less rain when moving! Perhaps some car in the future might.

14. ### phlogisticianBannedBanned

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It's all about the MOTION. or rather, the VOLUME of air the car moves through that contains rain, compared to the volume of rain that falls on the stationary car. All things being equal, the amount that falls on the top surfaces of the car won't vary much if it moving or sat still. But the front of the car sweeps through air containing rain, and therefore the car experiences more rain when moving.

It's so simple, how can you not understand this?

15. ### baftan*******Valued Senior Member

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how about the back of the car? Isn't it going to miss some rain?

16. ### EnmosRegistered Senior Member

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Yes, it does. The front of the car now catches raindrops that would otherwise have fallen on the ground before the car.

17. ### EnmosRegistered Senior Member

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How about plain old common sense.

18. ### SciencelovahRegistered Senior Member

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I am guessing, it depends on the speed of the rain, too. Don't mind me, my math and physic is poor :bawl:

19. ### EnmosRegistered Senior Member

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Hold out your hand, fingers pointing upwards.
Like this:

Now, imagine the rain coming straight from above while holding your hand still.
Next, imagine moving your hand away from you.
The vertical surface of your open hand will 'catch' the raindrops.

20. ### SciencelovahRegistered Senior Member

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Are you giving me face palm?

It's kinda difficult for me to imagine this thing without really calculating it.. so let's do a bit calculation..

Say a car has 1 meter square surface (exactly 1 x 1 m2). Then, oranges will be dropped from above to the car with speed of 1 orange per minute per m2 along 60 km length. So...

* how many oranges will hit the car if the car standing still for 1 hour in a fixed point?
* how many oranges will hit the car if the car travel for 1 hour with speed of 60 km/hour?

21. ### phlogisticianBannedBanned

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How does this differ when the car is moving, to standing still?

THINK.

22. ### OliHeute der Enteteich...Registered Senior Member

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Try thinking of it as air density (very roughly) - a moving car will have a higher density of air at the front than would a standing one, because it's moving into it - but since it's surrounded by air (the rain is coming down all over, not just where the car is), then it won't get any less at the back.

23. ### SciencelovahRegistered Senior Member

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Humm.. ok. How about my question at #17? Do I have to use integral or what?