Question: A Car In The Rain

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

  1. jmpet Valued Senior Member

    Messages:
    1,891
    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?
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. James R Just this guy, you know? Staff Member

    Messages:
    30,644
    If the rain is falling straight down, then the car gets more rain on it when it is driving.
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. jmpet Valued Senior Member

    Messages:
    1,891
    Yes, it's falling straight down.

    Why more rain?
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. chris4355 Registered Senior Member

    Messages:
    1,055
    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

    Messages:
    1,135
    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 R Just this guy, you know? Staff Member

    Messages:
    30,644
    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

    Messages:
    1,135
    Car doesn't present larger area when it is moving than it is stationary. Same surface, same rainfall...
     
  11. James R Just this guy, you know? Staff Member

    Messages:
    30,644
    But I just explained that it does, baftan.
     
  12. baftan ******* Valued Senior Member

    Messages:
    1,135
    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. mard Registered Member

    Messages:
    4
    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. phlogistician Banned Banned

    Messages:
    10,342
    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

    Messages:
    1,135
    how about the back of the car? Isn't it going to miss some rain?
     
  16. Enmos Staff Member

    Messages:
    43,184
    Yes, it does. The front of the car now catches raindrops that would otherwise have fallen on the ground before the car.
     
  17. Enmos Staff Member

    Messages:
    43,184
    How about plain old common sense.
     
  18. Sciencelovah Registered Senior Member

    Messages:
    4,349
    I am guessing, it depends on the speed of the rain, too. Don't mind me, my math and physic is poor :bawl:
     
  19. Enmos Staff Member

    Messages:
    43,184
    Hold out your hand, fingers pointing upwards.
    Like this:

    Please Register or Log in to view the hidden image!



    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. Sciencelovah Registered Senior Member

    Messages:
    4,349
    Are you giving me face palm?

    Please Register or Log in to view the hidden image!



    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?

    Please Register or Log in to view the hidden image!

     
  21. phlogistician Banned Banned

    Messages:
    10,342
    How does this differ when the car is moving, to standing still?

    THINK.
     
  22. Oli Heute der Enteteich... Registered Senior Member

    Messages:
    11,888
    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. Sciencelovah Registered Senior Member

    Messages:
    4,349
    Humm.. ok. How about my question at #17? Do I have to use integral or what?

    Please Register or Log in to view the hidden image!

     

Share This Page