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Trying to make sense of the strength to weight ratio

  1. Dec 8, 2015 #1
    I need some help with something that seems rather simple, but I don't know how to apply the formula. Let's say I have a table and based on the particular material from which it is constructed, it has a strength to weight ratio of 50 kN·m/kg. If I were to place an object on the table that weighed 50 kg, would I be able to use the strength to weight ratio to determine if the table is strong enough to support it?
     
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  3. Dec 8, 2015 #2

    DaveC426913

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    I do not think so - but I am no expert.

    The StW ratio of a table is highly dependent on the construction of the table.

    A useful StW ratio will be figured under specific conditions. For example, a beam of dimensions l x w x d made of steel will have a different StW of a comparable beam made of balsa.

    You can use that simple calculation to decide - in conjunction with engineering principles - to figure out how to make the table to support a given weight.
     
  4. Dec 8, 2015 #3
    Is that value for the material or for the table?
    Usually it is used as a material (and not object) property. I don't see how will be useful for an object.

    Even though is sometimes called strength-to-weight ratio, the usual meaning is that of the ration between the strength (in Pa or N/m2) and density (kg/m3).
    So it has nothing to do with the weight supported by an object made from this material.
    It is useful when you need to design something as light as possible for a given load or strength.

    For your question the strength will be all you need. I mean as material parameter. You need a lot of engineering experience (which I don't have). :)
     
  5. Dec 9, 2015 #4

    CWatters

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    There are several ways to measure "strength". Many materials are stronger in compression than in tension. So knowing how strong something is in tension may not help you design a table that has most of it's parts in compression. The design of the table may also put more load on some parts than others. You have to analyse the forces in each part and ensure each part is strong enough to handle it. Joints can be a weak point as they tend to concentrate forces.
     
  6. Dec 9, 2015 #5
    I guess I misunderstood the concept. What I am really trying to find out is a way to calculate how much weight an object can support based on its size, thickness, and its constituent material. I have done countless web searches and I can't seem to find the right terminology or formula.
     
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