Speed skating is a competitive form of ice skating in which the competitors race each other in traveling a certain distance on skates. Types of speed skating are long track speed skating, short track speed skating, and marathon speed skating. Short track speed skating takes place on a smaller rink, normally the size of an ice hockey rink. Distances are shorter than in long track racing, with the longest Olympic race being 3000 meters. Races are usually held as knockouts, with the best two in heats of four or five qualifying for the final race, where medals are awarded. Disqualifications and falls are not uncommon. The sport originates from pack-style events held in North America and was officially sanctioned in the 1970s, becoming an Olympic sport in 1992. Although this form of speed skating is newer, it is growing faster than long track speed skating, largely because short track can be done on an ice hockey rink rather than a long-track oval.

The Mayan languages form a language family spoken in Mesoamerica and northern Central America. Mayan languages are spoken by at least 6 million indigenous Maya, primarily in Guatemala, Mexico, Belize and Honduras. In 1996, Guatemala formally recognized 21 Mayan languages by name, and Mexico recognizes eight more. The Mayan language family is one of the best documented and most studied in the Americas. Modern Mayan languages descend from Proto-Mayan, a language thought to have been spoken at least 5,000 years ago.

The Doppler effect (or Doppler shift), named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

A perennial stream or perennial river is a stream or river (channel) that has continuous flow in parts of its stream bed all year round during years of normal rainfall. "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral" channels that flow only for hours or days following rainfall.

On this date in 1776, rebellious colonials launched the first modern democracy, an experiment in government controlled by the people themselves. America succeeded so well that virtually the entire world later adopted democracy with its guarantee of personal rights.