Bottom of a Bottle !

  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. berkeman

    Staff: Mentor

    What's a PET bottle?
  4. AlephZero

    AlephZero 7,244
    Science Advisor
    Homework Helper

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

  6. 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. thanks.

    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. Also, condensation along with a single flat surface would create a suction to the table which is not desirable.
  9. ahh nice hadn't thought of that! :)
  10. Well,
    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. the pressure argument makes sense!
    i meant more contact area when a bottle tips over!
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