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Thread: Falling beer bubbles...

  1. #1 Falling beer bubbles... 
    Forum Ph.D. william's Avatar
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    Hi everyone,
    As you probably are now aware, I like to pose these little questions. So here is another one.

    Let's say you are standing near a cliff. You crack open a bottle of beer and immediately let go of the bottle over the cliff (imagine it remains upright throughout the fall and no beer spills during the fall).

    So the question is this;
    which way do the bubbles move relative to the bottle during the fall?

    Cheers (literally ),
    william


    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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    Forum Sophomore L.E.A.P.'s Avatar
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    I got two answers... One I prefer and one that I dislike...

    First: The bubbles go out, as if the beer bottle is on a table.

    Second: The bubbles stay at the same place they were relative to the air before the beer bottle was dropped. Result: The gas stays there but the bottle says bye-bye.



    Did I get it right?


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  4. #3  
    Cooking Something Good MacGyver1968's Avatar
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    First off...dropping a perfectly good beer off a cliff....even in the name of science, should be a crime and considered alcohol abuse. j/k

    But seriously,

    My guess is that the bubbles would continue to rise in relation to the bottle. Holding the bottle in your hand, the bubbles would experience full gravity, yet their bouyant (sp?) nature make them float to the top. After being dropped, the beer would experience "weightlessness" from the free fall, so there would less force from gravity counteracting the bouyant force. The bubbles might even rise more quickly.

    Just watch out for a crazy Texan at the bottom of the cliff with a baseball glove yelling "I got it, I got it!"
    Fixin' shit that ain't broke.
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  5. #4  
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    First I thoght they would rise but everybody else said that so that got boring. Do they stay where they are? Maybe some kind of pressure gradient thing :? , no. I still think the bubbles would tend to rise.
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    Forum Sophomore L.E.A.P.'s Avatar
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    Ohhh, wait a minute!!!!!

    I think the bubbles are going to stay in the beer can because the bottle suffers weightlessness, but the gas that is lightert will not loose much weight, so the bubble's Volumic Mass will stay in the can because the beer's Volumic Mass will be almost equal to the gas's.

    Volumic Mass was translated from french so I don't know if it is the way we say it in english. We note it M/V
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    Alternate energy... or should we rather say alternate life?

    Are you interested in scientific high school projects? If you are, please contact me!

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    Forum Professor river_rat's Avatar
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    My guess from reading up on archimedies principle again is that the bubbles stay stationary wrt the bottle as the bouyancy force is equal to the weight of the fluid displaced by the bubbles.

    But as the beer is in free fall the fluid has no weight, so no bouyancy to drive the bubbles out of the liquid - so they stay stationary.

    anyway, thats my 2c worth.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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    Forum Sophomore L.E.A.P.'s Avatar
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    YES! I WAS RIGHT!

    Sorry, for my little moment of happiness
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    Alternate energy... or should we rather say alternate life?

    Are you interested in scientific high school projects? If you are, please contact me!

    "I must say that determination, devotion, and taking on challenges bigger then yourself is the way to become a master at anything" L.E.A.P.
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  9. #8  
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    I still think the gas pressure inside the liquid will be greater than that of the atmosphere outside and bubbles should still rise to the surface.
    What difference does it make if the bottle is accelerating downwards, the pressure gradient would still be there.
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    Forum Sophomore L.E.A.P.'s Avatar
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    If you have a glass of transparant glass at home, and a bottle of 7-Up, you might want to try this... The bubbles simply stay where they are...

    This is also right according to the buoyancy principal.
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    Alternate energy... or should we rather say alternate life?

    Are you interested in scientific high school projects? If you are, please contact me!

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  11. #10  
    Cooking Something Good MacGyver1968's Avatar
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    Quote Originally Posted by L.E.A.P.
    If you have a glass of transparant glass at home, and a bottle of 7-Up, you might want to try this... The bubbles simply stay where they are...
    I'm not quite following you. What are we supposed to try?
    Fixin' shit that ain't broke.
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    Forum Sophomore L.E.A.P.'s Avatar
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    You should put the 7-Up in the transparent glass and (without spilling it; it won't be me that will come and mop your floor), you should make a movement (as if the glass is falling).

    Take note of the bubbles, they will stay where they were before.
    P------------y--------------i----------------s
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    Alternate energy... or should we rather say alternate life?

    Are you interested in scientific high school projects? If you are, please contact me!

    "I must say that determination, devotion, and taking on challenges bigger then yourself is the way to become a master at anything" L.E.A.P.
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    Is it true to say that the bottle is weightless during its fall? Surely if it was weightless it wouldn't be falling anyway. I suppose the act of falling might mean that the pressure of the liquid does not vary with depth in the bottle, would that cause the bubbles to stay where they are?

    But the gas is still so much less dense than the liquid that I would imagine it would still want to escape........... William enlighten us before we cease to exist on this forum.
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  14. #13  
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    The bubbles will rise within the bottle UNLESS the air resistance is zero. If zero, the bottle will accelerate, the beer will not experience gravity, the density of the beer will be even throughout, therefore the bubbles will remain where they form. Since there WILL be some air resistance, the bubbles will rise but NOT as fast as if they were on the table.
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  15. #14  
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by billiards
    Is it true to say that the bottle is weightless during its fall? Surely if it was weightless it wouldn't be falling anyway. I suppose the act of falling might mean that the pressure of the liquid does not vary with depth in the bottle, would that cause the bubbles to stay where they are?

    But the gas is still so much less dense than the liquid that I would imagine it would still want to escape........... William enlighten us before we cease to exist on this forum.

    Hi billiards,
    Well, a few others have sufficiently answered this question already. But to specifically answer your post;

    Yes, an object in free-fall can be considered weightless (but not massless...).

    Your insight about the pressure not varying with depth is a good one.

    A final thought;
    Imagine you are asleep in an airplane. Suddenly the airplane does many barrel roles and ends up in free-fall after the wings break off. Since you were asleep and were dazed during the incident, you wake up disoriented to find yourself "floating" in the fuselage. Also imagine there are no windows on the airplane.

    Now... how would you know which direction was "up"?

    The same applies to the bubbles in the beer that was previously in the pilot's hand.

    The bubbles in a beer - when the net force on it is zero - wouldn't know which way to move.

    Bottoms up,
    william
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  16. #15  
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    I take it then young William that my hypothesis is correct in that any air resistance would create a microgravity environment and thus the bubbles would rise. Yes? no? maybe?
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  17. #16  
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    Quote Originally Posted by billco
    I take it then young William that my hypothesis is correct in that any air resistance would create a microgravity environment and thus the bubbles would rise. Yes? no? maybe?
    If the net force is not zero, then the bubbles would "know" which direction to move.

    So I guess the question is; "at terminal velocity, is the net force zero?"

    But in my original question I wasn't concerned with air resistance (which I failed to mention...).

    cheers
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  18. #17  
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    I just thought that if Planck had to be taken into considereation in my Hammer and Feather then why not air-resistance in your beer.
    Have you seen the one about the hole through the earth and dropping a rock in it?

    Science Forum Forum Index » Earth Sciences » humor me.
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  19. #18  
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    Quote Originally Posted by william
    If the net force is not zero, then the bubbles would "know" which direction to move.

    The bubbles in a beer - when the net force on it is zero - wouldn't know which way to move.
    Oops!
    This is not true as stated. Y'all let me get away with one.

    Should be;
    1. when the beer bottle is free to move, without restriction, the bubbles wouldn't "know" which direction to move.

    2. Another way is when the net force is zero - with all the forces being either "pulls" or "pushes" (but not a combination of the two) - the bubbles wouldn't know where to go.

    What made me reconsider this was thinking about a beer resting on a table. The net force is zero, but the bubbles know where to go. In this example, gravity is a "pull" but the table provides a "push".

    A falling beer is free to move (case 1) and a beer perfectly positioned between... say the moon and earth (Lagrangian point) has a net force of zero with both forces being "pulls" (case 2).

    Comment to billco; the air resistance would provide a "restriction," (albeit a small one) so the bubbles would move up (very slowly) in the presence of air resistance.

    Now will someone drink the damn beer!
    Cheers,
    wm
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  20. #19  
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    Why didn't you just say, When the bottle is in freefall and friction is ignored?

    Whoops! you are wrong Mr Smart Ass! as you drop the bottle, the bubbles will form and expand, as they do this, the volume of beer+ gas will increase, this will force the beer towards the opened top, this will move any bubbles also in the upper beer towards the top of the bottle.Even bubbles close to the bottom will be moved slightly.

    Now the REAL question is, Which hits the ground first? the bubbles or the beer? 8)
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  21. #20  
    Forum Ph.D. william's Avatar
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    Quote Originally Posted by billco
    Why didn't you just say, When the bottle is in freefall and friction is ignored?

    Whoops! you are wrong Mr Smart Ass! as you drop the bottle, the bubbles will form and expand, as they do this, the volume of beer+ gas will increase, this will force the beer towards the opened top, this will move any bubbles also in the upper beer towards the top of the bottle.Even bubbles close to the bottom will be moved slightly.

    Now the REAL question is, Which hits the ground first? the bubbles or the beer? 8)
    Then what happens if the beer bottle is being pushed downward (faster than free-fall velocity) Mr. smarty-pants?


    I could use a beer right now....

    cheers
    "... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
    ~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
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  22. #21  
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    do you mean by the outrush force of the air as it's displaced by the expanding beer, in an atmosphere that is increasing in density as the bottle falls?

    to answer your question the beer will be expelled, the bubbles will tend towards the bottom BUT the turbulent flow of the beer as it is expelled may override their exact path and destination of travel.
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  23. #22 Build A Fortune in Nursing Agency Business 
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  24. #23  
    Forum Freshman taxpo's Avatar
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    Yeah billiards is right
    l=l0[1+α(t-t0)]
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    i guess the bubble will just break up when we let the glass go. ha ha!
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