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3d shape definitions - when is a face a face and an edge and edge??

Discussion in 'Mathematics' started by Tomzy, Oct 12, 2010.

  1. Tomzy

    Tomzy New commenter

    When teaching 3d shapes at KS2 I have always taught that a face is a surface of a shape, e.g. a cube has 6 square faces, a cylinder has 3 faces, 2 circular and, if you 'unwrapped' it, 1 rectangular. It would therefore follow that a cube has 8 edges and a cylinder has 2, as an edge is where 2 faces meet. However, on looking at maths definitions on the internet, I read that a face is only the FLAT surface of a 3d shape and a face is NOT a curved surface. Therefore a cylinder has only 2 faces and as the faces do not meet, no edges.
    I've checked the QCA glossary and they also seem to say the same - defining an edge as where 2 plane surfaces meet.
    However (again) the other Y6 teacher disagrees with the above and agrees with my previous explanantion ( hope you're all following this)! As a result, we have both taught different definitions, throwing us, and the poor children, into complete confusion!
    PLEASE can some maths wizard advise!
  2. The curved part is part of the surface but I agree ... not a face

    Then again, what do I know ... I still want it to be a prism
  3. lilachardy

    lilachardy Star commenter

    A cube has 12 edges.
  4. oooops I missed that
  5. Tomzy

    Tomzy New commenter

    so did I! But it doesn't answer my question!
  6. Jeanie-Ju

    Jeanie-Ju New commenter

    I would say it has 3 faces - which would include the curved. I think as far as (silly)SATs & the like is concerned that would be what I would say to the children and they could then delve more deeply when older. I am, however, a mere mortal.
    Anyone know the decision behind heptagon and septagon??? I have been marking my children's work where they have labelled a seven sided shape as a septagon and I have never heard of it before (I promise I'm not completely stupid)!!! I have looked it up and it is a used word with the same definition but I wondered if there is a general idea of if it is an American-used word /old terminology /disliked term????????
    I have read of the origins but that doesn't help me to understand the use 'today'. Should i teach both?? Drop one??? I don't like 'septagon'. ;-(
  7. No, but I answered it in post 2
  8. septagon fits so nicely with octagon, nonagon, and decagon
  9. DM

    DM New commenter

    You can mark it correct. Either word is fine.
    I'm sure linguists would complain that septagon is a bit mangled as it has a Latin prefix and a Greek suffix.
  10. Nazard

    Nazard New commenter

    I must confess that it always feels slightly wrong to say "nonagon" for the same reason.
    But mathsisfun is happy with "septagon", so that settles it!
  11. DM

    DM New commenter

    mathsisfun has spoken.
  12. /new_thread[n=11]
    What about the hendecagon versus undecagon issue? 'Hen-' has the Greek advantage over the Latin 'un-' here, so fits with 'hepta-', but confusingly also has the backing of mathsisfun where 'hepta-' didn't. Now I don't know what to think! [​IMG]
  13. I call a 7-sided figure a 7-sided figure.
    No one studies Latin or Ancient Greek now,
    so lets make it easy for the kids.
  14. DM

    DM New commenter

    Maybe this is true of Ancient Greek but certainly not Latin. We now offer GCSE Latin (as an afterschool enrichment activity) in a bog standard comp - we had no choice really because all our feeder schools have Latin clubs.
    100,000 copies of Minimus have been sold to primary school children.
  15. Nazard

    Nazard New commenter

    You don't need to think - just read mathsisfun and believe!
  16. DM

    DM New commenter

    Teachers and students come and go but the word of mathsisfun is eternal.
  17. Nazard

    Nazard New commenter

    I had a moment of doubt and looked for an alternative to the Scripture According to Mathsisfun.
    I found this funny little website called "Wolfman MathWorld" (or something). It's really good that Were-wolves are able to be given these jobs and are able to be part of society, but I had to laugh when I saw the following:
    Heptagon: It is also sometimes called a septagon, though this usage mixes a Latin prefix sept- (derived from septua-, meaning "seven") with the Greek suffix -gon (from gonia, meaning "angle"), and is therefore not recommended.
    A hendecagon is an 11-sided polygon, also variously known as the undecagon or unidecagon. The term "hendecagon" is preferable to the other two since it uses the Greek prefix and suffix instead of mixing a Roman prefix and Greek suffix.
    Right - so mixing Latin and Greek is <u>bad</u> (things like "television" - won't ever catch on...).
    Imagine my surprise, etc, when I read this entry:
    The nonagon, also known as an enneagon, is a 9-sided polygon. Although the term "enneagon" is perhaps preferable (since it uses the Greek prefix and suffix instead of the mixed Roman/Greek nonagon), the term "nonagon," which is simpler to spell and pronounce, is used in this work.
    Consistency, conshmistency!
    I have learned my lesson, have purged myself with hyssop and am back in the mathsisfun fold for good. Hail mathsisfun! Hail mathsisfun!

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