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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.
Speed limit sign in the Republic of Ireland, using "km/h.". The SI representations, classified as symbols, are "km/h", "km h −1" and "km·h −1".Several other abbreviations of "kilometres per hour" have been used since the term was introduced and many are still in use today; for example, dictionaries list "kph", [3] [4] [5] "kmph" and "km/hr" [6] as English abbreviations.
Different from instantaneous speed, average speed is defined as the total distance covered divided by the time interval. For example, if a distance of 80 kilometres is driven in 1 hour, the average speed is 80 kilometres per hour. Likewise, if 320 kilometres are travelled in 4 hours, the average speed is also 80 kilometres per hour. When a ...
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.
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 ...
At 60 cycles per second, the wavelength is 5,000 kilometers, and even at 100,000 hertz, the wavelength is 3 kilometers. This is a very large distance compared to those typically used in field measurement and application. [4]
By combining many such measurements, a best fit value for the light time per unit distance could be obtained. For example, in 2009, the best estimate, as approved by the International Astronomical Union (IAU), was: [103] [104] light time for unit distance: t au = 499.004 783 836 (10) s, c = 0.002 003 988 804 10 (4) AU/s = 173.144 632 674 (3) AU/d.
Pace [6] in minutes per kilometre or mile vs. slope angle resulting from Naismith's rule [7] for basal speeds of 5 and 4 km / h. [n 1]The original Naismith's rule from 1892 says that one should allow one hour per three miles on the map and an additional hour per 2000 feet of ascent.