Statics and Equilibrium - Forces and Moments

Whilst learning about forces and moments it is extremely important to always refer every single question you attempt to the global reference axis system. (This is shown in the figure below.)

The global reference axis system determines whether or not a force or moment is of negative or positive magnitude and its direction on the application. This global reference can be rotted 90, 180 and even 270 degree's without an effect taking place, as long as you abide by the law.

Forces in the x and y direction are relatively simple, except in every single engineering question you will not necessarily be given the forces in this direction. You may be given the resultant force or an inclined force, and therefore it is vital to use trigonometry to work out the forces in the x and y direction and then add or subtract them accordingly. (Always use the global reference axis system)

The final part of this blog is moments. Moments are used when you have either a pin joint in the system (can support forces but not a moment), a pivot, or two or more variables missing from the final x and y equations. If this is the case then moments are used to determine a variable, and from there the remaining variables can be calculated in the x and y formulae. 

Shown below is a simple beam supported at one end, the three forces are forcing the moment anticlockwise (Global reference axis system deems this negative).