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.

Reserve Deputy Probation Officers are deputized volunteers who have received special training in order to assist Probation staff in a wide range of supervised responsibilities, that include direct involvement with juvenile an d adult probationers. Reserve Deputies are highly motivated, skilled, and caring people who want to serve their community as a part of the Los Angeles County Probation Department. Reserve Deputies are not a replacement for or an alternative to paid staff, but are intended to be an enhancement to existing resources.

The Republican Party, also commonly called the GOP (for "Grand Old Party"), is one of the two major contemporary political parties in the United States, the other being the Democratic Party. Founded by anti-slavery activists in 1854, it dominated politics nationally for most of the period from 1860 to 1932. There have been 18 Republican presidents, the first being Abraham Lincoln, serving from 1861 to 1865, and the most recent being Donald Trump who began serving in 2017.

In 2011, the Ohio Turnpike raised its limit to 70 and recorded its lowest traffic fatality rate ever that year. The higher speed limit attracts travelers to use the safer, limited-access, divided highways of the interstates from more traditional roads. That makes both types of roads safer.

The title Grandmaster is awarded to chess players by the world chess organization FIDE. Apart from World Champion, Grandmaster is the highest title a chess player can attain. Once achieved, the title is held for life.