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Centre of Gravity and Centroids

  1. Dec 4, 2015 #1
    1. The problem statement, all variables and given/known data
    http://puu.sh/lJgzB/5b877de108.jpg [Broken]

    http://puu.sh/lJgAR/c28393f051.jpg [Broken]

    Can someone please explain these two slides to me? Especially the first one, It seems to be summing the Moments in y and Moments in x. The sum of the moments in y is xW. I understand that but then it says that xW is equal to Sum of X times Change in W. Thats what I dont get. This is like the first page of the notes, theres no other info given. This is all.
    EDIT: Ive realised that we are assuming that the rigid body is made up of millions of tiny particles each at different distances(x) and different weights(W). So we sum it. But I still dont get why we use Delta W instead of W itself?
    2. Relevant equations


    3. The attempt at a solution
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Dec 4, 2015 #2

    SteamKing

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    Because W is the weight of the entire plate or piece of wire.
     
    Last edited by a moderator: May 7, 2017
  4. Dec 4, 2015 #3
    Why is Change in W used then?(delta W)
     
  5. Dec 4, 2015 #4
    Or is the Delta W just signifying the weight of the individual tiny particle that when summed together(sigma) results in the weight of the the rigid body?
     
  6. Dec 4, 2015 #5

    SteamKing

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    Right. ##W = \int dW ##
     
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