Editing Statics (section)

===Moment of a force===
In addition to the tendency to move a body in the direction of its application, a force can also tend to rotate a body about an axis. The axis may be any line which neither intersects nor is parallel to the [[line of action]] of the force. This rotational tendency is known as ''[[moment of force]]'' ('''M'''). Moment is also referred to as ''torque''.

====Moment about a point====
[[File:Diagram of the moment arm of a force F.svg|thumb|Diagram of the moment arm of a force F.]]
The magnitude of the moment of a force at a point ''O'', is equal to the perpendicular distance from ''O'' to the line of action of ''F'', multiplied by the magnitude of the force: {{nowrap|1=''M'' = ''F'' &middot; ''d''}}, where

: ''F'' = the force applied
: ''d'' = the perpendicular distance from the axis to the line of action of the force. This perpendicular distance is called the moment arm.

The direction of the moment is given by the right hand rule, where counter clockwise (CCW) is out of the page, and clockwise (CW) is into the page. The moment direction may be accounted for by using a stated sign convention, such as a plus sign (+) for counterclockwise moments and a minus sign (−) for clockwise moments, or vice versa. Moments can be added together as vectors.

In vector format, the moment can be defined as the [[cross product]] between the radius vector, '''r''' (the vector from point O to the line of action), and the force vector, '''F''':<ref>{{cite book|last=Hibbeler|first=R. C.|title=Engineering Mechanics: Statics, 12th Ed.|url=https://archive.org/details/staticsstudypack00russ|url-access=registration|year=2010|publisher=Pearson Prentice Hall|location=New Jersey|isbn=978-0-13-607790-9}}</ref>

:<math>\textbf{M}_{O}=\textbf{r} \times \textbf{F}</math>
:<math>r=\left(
\begin{array}{cc}
 x_{00} & ...  & x_{0j}\\
 x_{01} & ...  & x_{1j}\\
 ... & ... & ... \\
  x_{i0} & ...  & x_{ij}\\
 
\end{array}
\right)</math>
:<math>F=\left(
\begin{array}{cc}
 f_{00} & ...  & f_{0j}\\
 f_{01} & ...  & f_{1j}\\
 ... & ... & ... \\
  f_{i0} & ...  & f_{ij}\\
 
\end{array}
\right)</math>
:

====Varignon's theorem====
''[[Varignon's theorem (mechanics)|Varignon's theorem]]'' states that the moment of a force about any point is equal to the sum of the moments of the components of the force about the same point.