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The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).
SI, and hence the use of "km/h" (or "km h −1 " or "km·h −1 ") has now been adopted around the world in many areas related to health and safety [36] and in metrology [37] in addition to the SI unit metres per second ("m/s", "m s −1 " or "m·s −1 "). SI is also the preferred system of measure in academia and in education.
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 2.91 s or one mile in 4.69 s.
Miles per hour (mph, m.p.h., MPH, or mi/h) is a British imperial and United States customary unit of speed expressing the number of miles travelled in one hour.It is used in the United Kingdom, the United States, and a number of smaller countries, most of which are UK or US territories, or have close historical ties with the UK or US.
Tachymeter scale on a Citizen watch bezel. A tachymeter (pronounced / t æ ˈ k ɪ m ə t ər /) is a scale sometimes inscribed around the rim of an analog watch with a chronograph.It can be used to conveniently compute the frequency in inverse-hours of an event of a known second-defined period, such as speed (distance over hours) based on travel time (distance over speed), or measure distance ...
mile per hour: mph mph 1.0 mph (1.6 km/h) mph km/h; mile per second: mi/s mi/s 1.0 ...
0.51444 metres per second (approximately), 1.15078 miles per hour (approximately), 20.25372 inches per second (approximately) 1.68781 feet per second (approximately). The length of the internationally agreed nautical mile is 1 852 m. The US adopted the international definition in 1954, having previously used the US nautical mile (1 853.248 m). [6]
In the United States, it is computed per 100 million miles traveled, while internationally it is computed in 100 million or 1 billion kilometers traveled. According to the Minnesota Department of Public Safety, Office of Traffic Safety Volume of traffic, or vehicle miles traveled (VMT), is a predictor of crash incidence.