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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.
Abbreviations for "kilometres per hour" did not appear in the English language until the late nineteenth century. The kilometre, a unit of length, first appeared in English in 1810, [9] and the compound unit of speed "kilometers per hour" was in use in the US by 1866. [10] "Kilometres per hour" did not begin to be abbreviated in print until ...
Some airspeed indicators in aircraft prior to the mid-1970s indicate in miles per hour plus knots (1 knot = 1.15 mph) or kilometers per hour (1 knot = 1.85 km/h). A primary flight display with the indicated airspeed (IAS) displayed in the form of a vertical "tape" on the left.
1 knot (nautical mile per hour) 10 0: 1.2: ... a diving peregrine falcon—fastest bird; 320 km/h or 200 mph is a parameter sometimes used in defining a supercar. ...
As of May 15, 2017, 41 states have maximum speed limits of 70 mph (113 km/h) or higher. 18 of those states have 75 miles per hour (121 km/h) speed limits or higher, while 7 states of that same portion have 80 mph (129 km/h) speed limits, with Texas even having an 85 miles per hour (137 km/h) speed limit on one of its toll roads.
Research in 1998 showed that the reduction of some 30 mph (48 km/h) United Kingdom speed limits to 20 mph (32 km/h) had achieved only a 1 mph (1.6 km/h) drop in speeds and no discernible reduction in accidents; 20 mph (32 km/h) speed limit zones, which use self-enforcing traffic calming, achieved average speed reductions of 10 mph (16 km/h ...
The time it takes a vehicle to accelerate from 0 to 60 miles per hour (97 km/h or 27 m/s), often said as just "zero to sixty" or "nought to sixty", is a commonly used performance measure for automotive acceleration in the United States and the United Kingdom. In the rest of the world, 0 to 100 km/h (0 to 62.1 mph) is used.