Speed of light the "local" speed of light is constant and equal to "c", but the speed of light along a trajectory of finite length can differ from "c", depending on how distances and times are defined. It is generally assumed that fundamental constants such as "c" have the same value throughout spacetime, meaning that they do not depend on location and do not vary with time. However, it has been suggested in various theories that the speed of light may have changed over time. No conclusive evidence for such changes has been found, but they remain the subject of ongoing research. It
Road speed limits in the United Kingdom Road speed limits in the United Kingdom Road speed limits in the United Kingdom are used to define the maximum legal speed (which may be variable) for vehicles using public roads in the UK, and are one of the measures available to attempt to control traffic speeds. The speed limit in each location is indicated on a nearby traffic sign or by the presence of street lighting. Signs show speed limits in miles per hour (mph) or use the Clearway (or national speed limit (NSL)) symbol. The national speed limit is 70 mph (112 km/h) on motorways, 70 mph (112