With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Las Vegas is the most popular city in its country.
text_B: The angular momentum of light is a vector quantity that expresses the amount of dynamical rotation present in the electromagnetic field of the light .. angular momentum. angular momentum. light. light. vector. Euclidean vector. electromagnetic field. electromagnetic field. Indeed , a beam of light , while traveling approximately in a straight line , can also be rotating -LRB- or `` spinning '' , or `` twisting '' -RRB- around its own axis .. light. light. This rotation , while not visible to the naked eye , can be revealed by the interaction of the light beam with matter .. light. light. eye. eye. The total angular momentum of light -LRB- or , more generally , of the electromagnetic field and the other force fields -RRB- and matter is conserved in time .. angular momentum. angular momentum. light. light. electromagnetic field. electromagnetic field. force. force. But there are actually two distinct forms of rotation of a light beam , one involving its polarization and the other its wavefront shape .. light. light. polarization. Polarization ( waves ). wavefront. wavefront. These two forms of rotation are hence associated with two distinct forms of angular momentum , respectively named light spin angular momentum -LRB- SAM -RRB- and light orbital angular momentum -LRB- OAM -RRB- .. angular momentum. angular momentum. light. light. light spin angular momentum. light spin angular momentum. light orbital angular momentum. light orbital angular momentum
not_related.