Definition of a moment in statics? Please help

[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

 

[nlightner]

A moment in statics is a measure of the rotational force acting on an object around a specific point. It is calculated by multiplying the force applied to the object by the distance from the point of rotation to the line of action of the force. In the equation M=Fd, M represents the moment, F represents the force, and d represents the distance.

To determine if the moment is positive counterclockwise or negative clockwise, you must first establish a direction of rotation. This can be done by choosing a point on the object as the axis of rotation and defining it as either clockwise or counterclockwise. Then, you can determine the direction of the force relative to the axis of rotation. If the force is in the same direction as the chosen rotation, it is considered positive. If it is in the opposite direction, it is considered negative.

When dealing with components, you can calculate the moment for each individual component and then add them together to get the total moment. This can be done by using the same equation, M=Fd, for each component and then summing the individual moments together.

I hope this helps to clarify how to calculate moments in statics. If you are still confused, I recommend seeking help from a tutor or your instructor for further clarification and practice problems.