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Bernoullis equation- Open car window

  • 15-08-2011 11:10PM
    #1
    blacklionboy
    Registered Users, Registered Users 2 Posts: 100 ✭✭


    A quick question which was bugging me in the car today.

    Lets say you were driving down a motorway and you open a window slightly. The air around your car is moving very quickly relative to your car. So fast moving air(relative to observer) drops the relative pressure outside and would suck air out of the car.

    Now lets say the observer was standing on the motorway just beside where the car(or open window) passes. Relative to that observer, the air inside the car is moves quickly past and should be at a lower pressure? So how come air isn't sucked into the car for this reason?


Comments

  • #2
    Morbert
    Registered Users, Registered Users 2 Posts: 3,457 ✭✭✭Morbert


    blacklionboy wrote: »
    A quick question which was bugging me in the car today.

    Lets say you were driving down a motorway and you open a window slightly. The air around your car is moving very quickly relative to your car. So fast moving air(relative to observer) drops the relative pressure outside and would suck air out of the car.

    Now lets say the observer was standing on the motorway just beside where the car(or open window) passes. Relative to that observer, the air inside the car is moves quickly past and should be at a lower pressure? So how come air isn't sucked into the car for this reason?

    From the perspective of the observer standing on the motorway, the car is moving with the air, confining it and keeping its pressure high.

    A more extreme case is if you throw an open canister of high-pressure gas. Technically it is moving with respect to the air around it, but the pressure is being applied by the canister.


  • #3
    blacklionboy
    Registered Users, Registered Users 2 Posts: 100 ✭✭blacklionboy


    Morbert wrote: »
    blacklionboy wrote: »
    A quick question which was bugging me in the car today.

    Lets say you were driving down a motorway and you open a window slightly. The air around your car is moving very quickly relative to your car. So fast moving air(relative to observer) drops the relative pressure outside and would suck air out of the car.

    Now lets say the observer was standing on the motorway just beside where the car(or open window) passes. Relative to that observer, the air inside the car is moves quickly past and should be at a lower pressure? So how come air isn't sucked into the car for this reason?

    From the perspective of the observer standing on the motorway, the car is moving with the air, confining it and keeping its pressure high.

    A more extreme case is if you throw an open canister of high-pressure gas. Technically it is moving with respect to the air around it, but the pressure is being applied by the canister.

    Ah k that makes perfect sense! Cheers!


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