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    Edexcel AS physics

    I basically gathered from the edexcel book that brittleness is showing low plastic deformation. Unfortunately, I gathered that hardness too is showing low plastic deformation.
    If you have the exact definitions of brittleness and hardness, please help me out
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    No, hardness is the ease with which something is indented.

    edit: read up on the mohs scale if you have the edexcel text book.

    brittle: cracks and breaks without plstic deformation
    hard: not readily scratched or indented

    taken from the Salters Horners Edexcel AS physics book because I seem to have lost the just edexcel one

    this is the definition I have written in my revision notes (from using Edexcel text book and from Salters Horners Edexcel text book combined)

    Brittle – a material that breaks or cracks with little deformation e.g glass.
    Hard – materials which resist plastic deformation and are not easily scratched or indented e.g diamond.
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    Brittle things like glass do not deform elasticly very much and they yield after very little strain hence they are brittle.
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    (Original post by Maquillage)
    No, hardness is the ease with which something is indented.

    edit: read up on the mohs scale if you have the edexcel text book.

    brittle: cracks and breaks without plstic deformation
    hard: not readily scratched or indented

    taken from the Salters Horners Edexcel AS physics book because I seem to have lost the just edexcel one

    this is the definition I have written in my revision notes (from using Edexcel text book and from Salters Horners Edexcel text book combined)

    Brittle – a material that breaks or cracks with little deformation e.g glass.
    Hard – materials which resist plastic deformation and are not easily scratched or indented e.g diamond.
    What i infered is:
    scratched or indented: undergone plastic deformation
    Ask someone if these aren't the same thing :confused:
    but i will write down your definitions
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    (Original post by ssadi)
    What i infered is:
    scratched or indented: undergone plastic deformation
    Ask someone if these aren't the same thing :confused:
    but i will write down your definitions
    ok my definitions basically say it all :/

    although they both show "low plastic deformation" as you call it, they do it in different ways.

    Plastic deformation is when something goes past its elastic limit and is unable to return to its original form.


    Brittle things crack and break without showing it.
    Hard things resist it.
    subtle differences in wording.

    have you covered extension force or stress strain graphs yet? this can help you in understanding, I think they're in both Edexcel text books. I'll go and have another look for my one.
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    (Original post by DeeDub)
    Brittle things like glass do not deform elasticly very much and they yield after very little strain hence they are brittle.
    How do you define hardness then, just cutting of the "they yield after very little strain" part?
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    (Original post by Maquillage)
    ok my definitions basically say it all :/

    although they both show "low plastic deformation" as you call it, they do it in different ways.

    Plastic deformation is when something goes past its elastic limit and is unable to return to its original form.


    Brittle things crack and break without showing it.
    Hard things resist it.
    subtle differences in wording.

    have you covered extension force or stress strain graphs yet? this can help you in understanding, I think they're in both Edexcel text books. I'll go and have another look for my one.
    What do you think of this:
    http://www.thestudentroom.co.uk/show...16&postcount=6
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    (Original post by ssadi)
    How do you define hardness then, just cutting of the "they yield after very little strain" part?
    Hardness is defined empirically using the Vickers or Rockwell test. A materials is said to be harder than another if it can cause an indentation in the surface of the other material. Hence diamond is hard than steel because diamond can indent steel. Steel is harder than chalk because steel can indent chalk. The reverse of both is not true and hence steel is softer than diamond and chalk is softer than steel.
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    (Original post by DeeDub)
    Hardness is defined empirically using the Vickers or Rockwell test. A materials is said to be harder than another if it can cause an indentation in the surface of the other material. Hence diamond is hard than steel because diamond can indent steel. Steel is harder than chalk because steel can indent chalk. The reverse of both is not true and hence steel is softer than diamond and chalk is softer than steel.
    ^ this. I think that also has something to do with the Mohs scale but I'm not sure.
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    (Original post by Maquillage)
    ^ this. I think that also has something to do with the Mohs scale but I'm not sure.
    The mohs scale is used to rank different materials so there hardnesses can be compared but it is an empirical scale. That is to say that fluorite which is four on the mohs scale is not necessarily twice as hard as gypsum which is two. According to wiki Fluorite is in fact seven times harder.
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    (Original post by DeeDub)
    Brittle things like glass do not deform elasticly very much and they yield after very little strain hence they are brittle.
    Another thing, does brittle means:
    Do not show much elastic deformation+
    Do not show much plastic deformation+
    breaks after little strain?
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    (Original post by ssadi)
    Another thing, does brittle means:
    Do not show much elastic deformation+
    Do not show much plastic deformation+
    breaks after little strain?
    Breaks after little strain, but if it breaks after little strain then the first two are also true but they follow on from the third point. Things which can withstand high strain are 'tough'. Steel is tougher than cast iron.
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    (Original post by ssadi)
    Edexcel AS physics

    I basically gathered from the edexcel book that brittleness is showing low plastic deformation. Unfortunately, I gathered that hardness too is showing low plastic deformation.
    If you have the exact definitions of brittleness and hardness, please help me out
    hard means wont deform when you put general pressure on it.
    brittle means when you put a lot of pressure on it over a smaller area, it will break.
    both are low plastic deformation, but they do not mean exactly the same thing.
    glass is hard and brittle. wood is hard and not brittle. iron is hard and britlle. steel is hard and not brittle.
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    (Original post by Deedub)
    .
    (Original post by Maquillage)
    .
    Thanks for sorting this out for me:
    Conclusion:
    brittleness: low elastic+plastic deformation+breaks after little strain
    hardness: relative indenting power/ resistance to plastic deformation

    Reward for the help
    (May come handy)
 
 
 
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