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Bottom of a Bottle !

  1. Feb 24, 2013 #1
    why does the bottom of any average PET bottle have those 'bumps' instead of being flat?
    does it have something to do with improving the balance, if so how?
  2. jcsd
  3. Feb 25, 2013 #2


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    What's a PET bottle?
  4. Feb 25, 2013 #3


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  5. Feb 26, 2013 #4
    i meant any plastic (other than glass) bottle generally used for storing cold-drinks, water etc.

  6. Feb 26, 2013 #5
    For stability during production, filling, and end-user use. The factory uses the feet to position the bottles in the factory for various purposes, the end-user relies on them so the bottle doesn't tip over easily. You'll see them in bottles which have internal pressure as the legs are much more rigid than a large flat surface and will remain fairly constant in their shape, making the bottle more stable when unopened, even after a long, bumpy transport.
  7. Feb 26, 2013 #6

    how are multiple curved surfaces more suitable for balance as compared to a single flat one?
    is it because they account for a larger contact surface area?
  8. Feb 26, 2013 #7
    Also, condensation along with a single flat surface would create a suction to the table which is not desirable.
  9. Feb 26, 2013 #8
    ahh nice hadn't thought of that! :)
  10. Feb 26, 2013 #9
    1) The bottles are plastic and so a flat bottom surface would, if unsupported, deflect under pressure creating a bubble on the bottom which would be horrible for stability. Not to mention it would be a pretty poor design as far as pressure vessels are concerned.

    2) The legs have less overall surface area touching the table, but they are consistent in shape.

    3) There are bottles which do not have the legs, but instead have a round rim along the bottom with the center recessed (so only the rim touches the table or other surface). This is for the same reason. A rigid area to stand the bottle on which will not deform under pressure.
  11. Feb 26, 2013 #10
    the pressure argument makes sense!
    i meant more contact area when a bottle tips over!
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