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Adding Vectors (2 laws)

  1. Oct 19, 2005 #1
    when do i use
    Paralleogram Law of Vector Addition

    and when

    THe Triangle law of vector addition

    will they always give the same answer for vector a + vector b?
    this is relaly confusing me thanks!
  2. jcsd
  3. Oct 19, 2005 #2


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    Homework Helper

    Adding two vectors will require the parallelogram rule. If you'd want to substract to vectors, you can either use the triangle rule or again the parallelogram rule, but then adding the opposite vector.

    Check Vector addition
  4. Oct 19, 2005 #3
    so u cant add using tirangle law
    i heard it gives same result
  5. Oct 19, 2005 #4
    Just add the components!
  6. Oct 20, 2005 #5


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    Substracting an opposite vector will gave the same result as adding it, of course.

    I think I know see what you mean. When two vectors have the same origin, you use the parallelogram rule.
    Perhaps you're thinking of two vectors placed 'in serie', so one starts where the other ends. Then you can make the sum by contructing the triangle. The parallelogram rule will work here as well, by placing the second vector's tail where the first one starts.
    Last edited: Oct 20, 2005
  7. Oct 20, 2005 #6


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    Half of a parallelogram is a triangle- and since all the information given in the parallelogram is also present in the triangle you don't really need to draw the whole parallelogram. I think by "triangle law" you are simply referring to apply trigonometry (the sine and cosine laws in particular) to half the parallelogram.
  8. Sep 11, 2011 #7
    hey will u please explain me the whole concept...becoz tmmorw is my physics test...
    pls help...
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