Direction of a moment

1. Nov 21, 2013

sevag00

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.

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

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. Nov 21, 2013

Anyway,moment =Force x Perpendicular distance

3. Nov 21, 2013

sevag00

I know how to find the magnitude. I'm asking for the direction.

4. Nov 21, 2013

If you know it,then show your work.
PF requires one to show his/her work before getting any help(In the homework section)

5. Nov 21, 2013

sevag00

Yeah. But first i should find the direction of the moments of the components of the force so that i get the right result.

6. Nov 21, 2013

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:

Look at diagram a,Force F produces an Anticlockwise moment.
Look at diagram b,Force F now produces a Clockwise moment.

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7. Nov 22, 2013

sevag00

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.

8. Nov 22, 2013

9. Nov 22, 2013

sevag00

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.