1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Direction of a moment

  1. Nov 21, 2013 #1
    Hi. I'm really confused in how to find the moment done by force.

    I want to find the moment done by the force in this figure.

    Capture.jpg

    The book has resolved the force into its components using principle of moments.

    Capture1.jpg

    So, how do i find the moments of the components of the force? I know i'm going to use the right hand rule, but i don't know where i am going to put my thumb.
     
  2. jcsd
  3. Nov 21, 2013 #2

    adjacent

    User Avatar
    Gold Member

    Show your work please.
    Anyway,moment =Force x Perpendicular distance
     
  4. Nov 21, 2013 #3
    I know how to find the magnitude. I'm asking for the direction.
     
  5. Nov 21, 2013 #4

    adjacent

    User Avatar
    Gold Member

    If you know it,then show your work.
    PF requires one to show his/her work before getting any help(In the homework section):smile:
     
  6. Nov 21, 2013 #5
    Yeah. But first i should find the direction of the moments of the components of the force so that i get the right result.
     
  7. Nov 21, 2013 #6

    adjacent

    User Avatar
    Gold Member

    You don't need to calculate that.Moment is a turning effect.It does not have any directions.It has direction of rotation.You just have to use common sense and decide whether it's anticlockwise or clockwise
    For example,look at this:
    attachment.php?attachmentid=64172&stc=1&d=1385061988.gif
    Look at diagram a,Force F produces an Anticlockwise moment.
    Look at diagram b,Force F now produces a Clockwise moment.

    Think about your diagram now
     

    Attached Files:

  8. Nov 22, 2013 #7
    Okay. But there is something called right hand rule that you indirectly used to find the direction of (a) and (b).
    I want to know how the right hand rule is used.
     
  9. Nov 22, 2013 #8

    adjacent

    User Avatar
    Gold Member

  10. Nov 22, 2013 #9
    I know what your saying. Your taking a direction vector from point O to the line of action of the force. And by using cross product, you're getting the magnitude and direction. But i'm not using that method. I'm using Varignon's theorem.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted