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Thread: What causes things like this to happen?

  1. #1 What causes things like this to happen? 
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    What is it called when you put something like a plastic grocery bag on the edge of a table and it stays and sits there on the table for a few minutes, but a few minutes later it falls off the edge of the table onto the ground?


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  3. #2  
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    If it is in an unstable situation, it could be a small vibration or a slight wind current.


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  4. #3 Re: What causes things like this to happen? 
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    Quote Originally Posted by noSkillz
    What is it called when you put something like a plastic grocery bag on the edge of a table and it stays and sits there on the table for a few minutes, but a few minutes later it falls off the edge of the table onto the ground?
    Quite often it is called spilled milk.
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    DrRocket

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  6. #5 Re: What causes things like this to happen? 
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    Quote Originally Posted by noSkillz
    What is it called when you put something like a plastic grocery bag on the edge of a table and it stays and sits there on the table for a few minutes, but a few minutes later it falls off the edge of the table onto the ground?
    It's called a normal response to gravity.
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    Quote Originally Posted by noSkillz
    DrRocket

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    Then don't post garbage and formulate your questions clearly and precisely.
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  8. #7  
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    Quote Originally Posted by noSkillz
    DrRocket

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  9. #8 Re: What causes things like this to happen? 
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    Quote Originally Posted by noSkillz
    What is it called when you put something like a plastic grocery bag on the edge of a table and it stays and sits there on the table for a few minutes, but a few minutes later it falls off the edge of the table onto the ground?
    Non-linearity? Chaos? Is this what you're trying to get at?

    You can never know the initial conditions of the system exactly so as the system evolves it's possible for unexpected behaviour to occur. In this case the seemingly static shopping bag suddenly collapses.

    But this is only because you don't know the initial conditions exactly, that is you don't know exactly what tiny fluctuations are going on with the bag or what's happening with the food inside the bag.

    Hope this helps, if this was what you were trying to talk about.

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  10. #9 accelaration 
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    I would suggest that the item/s were ALWAYS moving, if even slightly, and over time gravity wins.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  11. #10  
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    Its only that the centre of gravity of the bag and the things in it making it a system in a whole, shifts to a point with the alignment of things inside the bag due to its own weight, where it loses the balance and fells down. Its just like that person who walks on the rope with a long stick to vary the centre of gravity to balance out the imbalance, but if unfortunately he fails to maintain that point, he falls down.
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  12. #11  
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    If you lay a sheet of paper or I suppose a plastic bag, on a flat surface, there will be a layer of air trapped underneath, and that will take some time to flow out from under. Until then, the air is providing a lubricating cushion and the sheet of paper will slide off the table, if it's not quite flat. That only lasts a few seconds though, not minutes, so that's probably not what you are referring to.
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    If this is about an empty bag I suppose the bag is electricaly charged a little relative to the table. The static charge slowly disappears from the bag and the tack to the table disappears with it.
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  14. #13  
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    the entropic and therefore chaotic nature of all atoms

    all atoms are bound by forces true, but there are forces microscopically stronger seeking to pull them apart, making everything evenly distributed through all space


    a balanced bag toppling is a visible example of this
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  15. #14  
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    I would think that it is gravity and the structure of the object. A bag isn't solid so it is probably slowly caving in and finally something breaks and it falls when it has finally become off balance.

    If you had a more solid structure that was light and no current or vibrations as was mentioned it would stay there.
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  16. #15  
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    I know what you mean. Thump! A standing bag of chips or a book suddenly "decides" to flop over. Or, Click!, part of a crumpled soda can suddenly "decides" to uncrumple itself a little bit. Or, Kerclunk!, ice cubes in a glass suddenly "decide" to shift. Small forces act on objects all around us. Often it occurs with little effect that we can notice. Sometimes the book or the bag of chips undergoes a shift in mass sufficient to cause it to topple. Or the uncrumpling can passes a certain point where one of its facets click back toward its original shape.

    You asked for the name of it. Overall, the scientific subject you ask about is called "catastrophe theory" and the specific event you describe is called a "cusp catastrophe".

    A "cusp catastrophe" is often illustrated using a wrinkled surface representing the state of situation (see below). There are slopes, one side where the situation can transition from one state to another gradually (down a steady slope). However, another part of the surface is wrinkled, causing the upper surface to overlap the lower surface, which results in a "cusp" (that is, a cliff). Transitioning down this part of the slope is obvious: once over the edge of the cusp, the situation's state changes quite abruptly.

    I hope this helps.

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