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Thread: straws in water

  1. #1 straws in water 
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    hello, when u place a group of short straws in water, they float and stick together. What forces are acting on the straws that make them stick together?

    if you cut them up into 1 cm lengths, and let them float on water by themselves, they started to arrange themselves usually side by side, or end to end. However they rarely join perpendicular to each other. If i knew what forces make the straws stick together i'd understand this, but im not too sharp.

    Can any one explain this to me?


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  3. #2  
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    ive said this before and Ill say it again... dont take my words as fact! I like to give my opinoin anyways. Floating and sinking are due to density. Straws aren't very dense so they float when they are on their own. But when there is a whole bunch of straws the bouyant point is higher which causes it to sink more but still mostly remain over the water. As for the cut up pieces... I think it may have to do with the motion of the water. The waves would flow THROUGH the straw which would cause them to all turn the same way. Hence them lining side by side.


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  4. #3  
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    It's called the Cheerio effect and is caused by surface tension.

    http://en.wikipedia.org/wiki/Cheerio_effect
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  5. #4  
    Forum Sophomore basim's Avatar
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    is it always attaching side by side, not side and an end?
    God is one and only.

    God knows the best.
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  6. #5  
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    You ever think that something is going to be really simple and then it isn't? The cheerio effect sounds simple, then there is a monster equation. If something is going to be difficult, I think it should have a confusing name as a warning.
    http://img216.imageshack.us/img216/6164/thinghl2.jpg
    "We make our world significant by the courage of our questions and by the depth of our answers." -Carl Sagan
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  7. #6  
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    You ever think that something is going to be really simple and then it isn't? The cheerio effect sounds simple, then there is a monster equation. If something is going to be difficult, I think it should have a confusing name as a warning.
    Keith, I agree with you. I posted that link to Wikipedia but after I read it, I didn't think it explained it very well. I think they threw in that hairy equation just to show off. If you google "cheerio effect" you can find some better articles.

    The way I think of it is like this. There is an attraction between the water molecules in the surface of the milk. That's what makes the surface film that water bugs can walk on. There is also an attraction between the water and the solid objects like the Cheerios. That's what makes a meniscus like you may have seen in your Chemistry class where it looks like the water is trying to climb up the sides of a test tube. So now you have two cheerios coming together and each one has a meniscus climbing up the side of it. When they touch, the two meniscuses (is that a word?) come together and attract each other and pull the two cheerios together.
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    and they go side by side because the sides have a larger surface area therefore a larger miniscus?
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  9. #8  
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    and they go side by side because the sides have a larger surface area therefore a larger miniscus?
    The way I think it works is they kind of float around randomly until they touch. But once they touch, the two meniscuses are attracted together and combine and they want to stay together because it takes some force to pull the water apart into two separate meniscuses.

    Another way of saying it would be the attraction of the liquid surface is trying to minimize the surface area, and if two cheerios are touching there is less liquid surface than if the cheerios were separate, each with its own meniscus.
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  10. #9  
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    ya but im asking if thats why they line up side by side rather than side to end
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  11. #10  
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    ya but im asking if thats why they line up side by side rather than side to end
    Oh, now I get what you are saying. Yes, I agree with that.

    I just thought of another way to think about surface tension - a trampoline. The trampoline is some stretchy material attached to a frame. Each part of the trampoline surface is "attracted" to any adjacent part by the elasticity of the material like the molecules of water are attracted to each other. When you walk across a trampoline, it dents in where you step on it, like the water bug's feet dent in the water surface. Around the outer edge of the trampoline you have springs connecting the surface of the fabric to the frame, and these springs are always in tension. The springs would be like the meniscus that attaches the water surface to the edge of the test tube. So the meniscus is like a row of springs always pulling the solid object in toward the pool of liquid.
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