student :what is moment?
prof: moment is a rotational force......wait
                              just see this diagram

in this diagram the person a is 1000newton ant he is at a distance of 1m from the center
 now inorder to be in equlibrium the clockwise moment must be equal to anticlockwise moment... so the guy who is 500newton is at a distance 2m apart...else the guy b will go up
student:why we learn this?
prof:for machiene design such as microscope,bicycle and motorbikes...we need to use calculation...so moment is a terminology used for calculations so as to avoid failure or increase effectiveness of cycles or any vehicle

                             eg: