How Do You Determine the Direction of a Moment in Statics?

[th3plan]

Homework Statement

How do i know how to calculate it properly ? Like i Know M=Fd but, how can i tell if its positve counterclockwise or negative clockwise. Expecially when you have components.

Something Like this that's broken into compoents how can i calculate the moment ? I am totally confused on how it goes

 

[LowlyPion]

Let's assume you are talking about Torque, which is force taken through a moment arm.

Take 1 direction to be positive. I use the right hand rule generally - which means counter-clockwise with the Torque arrow pointing up.

Resolve the force arrows with respect to x,y so that you have a representation that looks like

F = a i + b j

Then the point at which a line along and through the force intersects the x or y axis, then the product of the distance along the axis times the component perpendicular to the axis is your Torque.

For instance in your example at B the Torque will be + F_By*B along the x axis.

Alternatively, you can project the line of the Force vector to a line that is perpendicular with the pivot and then just take the product.

A quick search yielded this link that more or less says the same thing.
http://www.physics.uoguelph.ca/tutorials/torque/Q.torque.intro108.html