Mile per Hour is a unit of measure used in the United Kingdom and the United States to express speed in terms of the number of ground miles traveled for one hour. The acronym used to abbreviate mile per hour is mph. It should be noted that there are several types of miles (such as the land mile or the sea mile), so the conversion of speeds specified in miles per hour depends on the context in which it is inserted. Several English-speaking countries use this speed measure to set boundaries on roads. Interestingly, Canada is one of the few countries in the world, at which train speed is measured in miles per hour, but the speed of the cars on the roads is measured in kilometers per hour.
The Knot is a unit of measure of speed, which has a direct correspondence with the nautical miles per hour, which in turn are related to the curvature of the Earth. It should be noted that since the knot is a measure of speed, one should not say knot per hour, since in this case (when measuring velocity versus time) we would be talking about acceleration rather than velocity. This unit is usually used for sea and air transportation. In the past, one of the most common ways of estimating a ship's speed was to launch from the stern of the boat a float connected by a cable that had knots made at regular distances. That said, as the boat moved away from the float, we counted the number of knots that were dropped during a certain time, measured at that time by the emptying of an hourglass.