Miles per hour in the context of "Speed"

The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.92 s or one mile in 4.69 s. It depends strongly on temperature as well as the medium through which a sound wave is propagating.

At 0 °C (32 °F), the speed of sound in dry air (sea level 14.7 psi) is about 331 m/s (1,086 ft/s; 1,192 km/h; 740 mph; 643 kn).

Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed, expressed as kilometres per hour (km/h) or miles per hour (mph) or both. Speed limits are commonly set by the legislative bodies of national or provincial governments and enforced by national or regional police and judicial authorities. Speed limits may also be variable, or in some places nonexistent, such as on most of the Autobahnen in Germany.

The first numeric speed limit for mechanically propelled road vehicles was the 10 mph (16 km/h) limit introduced in the United Kingdom in 1861.

A Category 5 Atlantic hurricane is a tropical cyclone that reaches Category 5 intensity on the Saffir–Simpson hurricane wind scale, within the Atlantic Ocean to the north of the equator. They are among the strongest tropical cyclones that can form on Earth, having 1-minute sustained wind speeds of at least 137 knots (254 km/h; 158 mph; 70 m/s). The United States National Hurricane Center (NHC) currently estimates that 11 tropical cyclones between 1851 (the first Atlantic hurricane season to be included in the official Atlantic tropical cyclone record) and 1959 peaked as Category 5 hurricanes. However, because technologies such as satellite monitoring were not available until the 1960s, some cyclones may have remained undetected. Since 1960, 34 Atlantic hurricanes have reached Category 5.

A gale is a strong wind; the word is typically used as a descriptor in nautical contexts. The U.S. National Weather Service defines a gale as sustained surface wind moving at a speed between 34 and 47 knots (63.0 and 87.0 km/h; 17.5 and 24.2 m/s; 39.1 and 54.1 mph). Forecasters typically issue gale warnings when winds of this strength are expected. In the United States, a gale warning is specifically a maritime warning; the land-based equivalent in National Weather Service warning products is a wind advisory.

Other sources use minima as low as 28 knots (52 km/h; 14 m/s; 32 mph), and maxima as high as 90 knots (170 km/h; 46 m/s; 100 mph). Through 1986, the National Hurricane Center used the term “gale” to refer to winds of tropical force for coastal areas between 33 knots (61 km/h; 17 m/s; 38 mph) and 63 knots (117 km/h; 32 m/s; 72 mph). The 90 knots (170 km/h; 46 m/s; 100 mph) definition is very non-standard. A common alternative definition of the maximum is 55 knots (102 km/h; 63 mph; 28 m/s).

The true airspeed (TAS; also KTAS, for knots true airspeed) of an aircraft is the speed of the aircraft relative to the air mass through which it is flying. The true airspeed is important information for accurate navigation of an aircraft. Traditionally it is measured using an analogue TAS indicator, but as GPS has become available for civilian use, the importance of such air-measuring instruments has decreased. Since indicated, as opposed to true, airspeed is a better indicator of margin above the stall, true airspeed is not used for controlling the aircraft; for these purposes the indicated airspeed – IAS or KIAS (knots indicated airspeed) – is used. However, since indicated airspeed only shows true speed through the air at standard sea level pressure and temperature, a TAS meter is necessary for navigation purposes at cruising altitude in less dense air. The IAS meter reads very nearly the TAS at lower altitude and at lower speed. On jet airliners the TAS meter is usually hidden at speeds below 200 knots (370 km/h). Neither provides for accurate speed over the ground, since surface winds or winds aloft are not taken into account.

The United Kingdom has a well developed and extensive network of roads totalling about 262,300 miles (422,100 km). Road distances are shown in miles or yards and UK speed limits are indicated in miles per hour (mph) or by the use of the national speed limit (NSL) symbol. Some vehicle categories have various lower maximum limits enforced by speed limiters. A unified numbering system is in place for Great Britain, whilst in Northern Ireland, there is no available explanation for the allocation of road numbers.

The earliest specifically engineered roads were built during the prehistoric British Iron Age. The road network was expanded during the Roman occupation. Some of these roads still remain to this day. New roads were added in the Middle Ages and from the 17th century onwards. Whilst control has been transferred between local and central bodies, current management and development of the road network is shared between local authorities, the devolved administrations of Scotland, Wales and Northern Ireland, and National Highways in England. Certain aspects of the legal framework remain under the control of the United Kingdom parliament.