Conservation law, also called law of conservation, in physics, several principles that state that certain physical properties (i.e., measurable quantities) do not change in the course of time within an isolated physical system. In classical physics, laws of this type govern energy, momentum, angular momentum, mass, and electric charge.
On New Yearâs Eve, the Metrorail system will open at 7 a.m. with special extended service on all lines until 3 a.m. The additional three hours of service â consistent with past years â is a special exception to a moratorium on extended hours during the year-long SafeTrack maintenance program.
75Â¢. 1  Off-Peak hours include weekdays 9am - 3pm and 7pm - 5am; weekends and Federal holidays. 2  Metro bus operators do not carry change. 3  Two children under age 5 may travel free with each fare-paying adult on bus or rail.  Eating, drinking or smoking is not permitted in Metro stations, buses or trains.