Kilometer/hour (km/h)
Definition: The kilometer per hour (symbol: km/h) is a unit of speed expressing the number of kilometers traveled in one hour. It is the most common unit of speed in the world, used in most countries for road speed limits and vehicle speedometers.
History/origin: The kilometer per hour is derived from the kilometer (1,000 meters) and the hour (3,600 seconds). It was introduced as part of the metric system in the late 18th century and became widely adopted globally in the 20th century.
Current use: The km/h is used worldwide for measuring speed limits, vehicle speeds, and in various sports like athletics and cycling. It is the standard unit of speed in most countries outside the United States and United Kingdom.
Mile/hour (mi/h)
Definition: The mile per hour (symbol: mph) is a unit of speed expressing the number of miles traveled in one hour. It is primarily used in the United States and United Kingdom for road speed limits and vehicle speedometers.
History/origin: The mile per hour is derived from the mile (5,280 feet or 1,609.344 meters) and the hour (3,600 seconds). It has been used since the 18th century and remains the standard unit of speed in the US and UK.
Current use: The mph is used in the United States, United Kingdom, and a few other countries for measuring speed limits, vehicle speeds, and in sports like NASCAR and Formula 1.