AskDefine | Define promptness

Dictionary Definition



1 the characteristic of doing things without delay [syn: promptitude]
2 the quality or habit of adhering to an appointed time [syn: punctuality] [ant: tardiness]

User Contributed Dictionary



  • /ˈprɒmptnəs/



  1. The quality or characteristic of doing things without delay.
  2. The habit of adhering to a designated time.



Extensive Definition

Speed is the rate of motion, or equivalently the rate of change in position, often expressed as distance d traveled per unit of time t.
Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as velocity. Speed is measured in the same physical units of measurement as velocity, but does not contain the element of direction that velocity has. Speed is thus the magnitude component of velocity.
In mathematical notation, it is simply:
v = \left|\frac \right|.
Note that "v" is the variable for speed.
Objects that move horizontally as well as vertically (such as aircraft) distinguish forward speed and climbing speed.


Units of speed include:
Mach 1 ≈ 343 ms-1 ≈ 1235 km/h ≈ 768 mph in dry air at sea-level pressure and 293 kelvin (See Speed of sound for more detail.)
c = 299,792,458 ms-1
  • Other important conversions
1 m/s = 3.6 km/h
1 mph = 1.609 km/h
1 knot = 1.852 km/h = 0.514 ms-1
Vehicles often have a speedometer to measure the speed they are going.

Average speed

Speed as a physical property represents primarily instantaneous speed. In real life we often use average speed (denoted |\tilde|), which is rate of total distance (or length) and time interval. For example, if you go 60 miles in 2 hours, your average speed during that time is 60/2 = 30 miles per hour, but your instantaneous speed may have varied.
In mathematical notation:
|\tilde| = \frac
Instantaneous speed defined as a function of time on interval [t_0, t_1] gives average speed:
|\tilde| = \frac
while instant speed defined as a function of distance (or length) on interval [l_0, l_1] gives average speed:
|\tilde| = \frac
It is often intuitively expected, but incorrect, that going half a distance with speed |v|_ and second half with speed |v|_, produces total average speed |\tilde| = \frac. The correct value is |\tilde| = \frac (Note that the first is a proper arithmetic mean while the second is a proper harmonic mean).
Average speed can be derived also from speed distribution function (either in time or on distance):
|v| \sim D_t\; \Rightarrow \; |\tilde| = \int |v| D_t(|v|) \, dv
|v| \sim D_l\; \Rightarrow \; |\tilde| = \frac

Examples of different speeds

Below are some examples of different speed (see also main article Orders of magnitude (speed)):
  • Speed of a common snail = 0.001 ms-1; 0.0036 km/h; 0.0023 mph.
  • A brisk walk = 1.667 ms-1; 6 km/h; 3.75 mph.
  • Olympic sprinters (average speed over 100 metres) = 10 ms-1; 36 km/h; 22.5 mph.
  • Speed limit on a French autoroute = 36.111 ms-1; 130 km/h; 80 mph.
  • Top cruising speed of a Boeing 747-8 = 290.947 ms-1; 1047.41 km/h; 650.83 mph; (officially Mach 0.85)
  • Official air speed record = 980.278 ms-1; 3,529 km/h; 2,188 mph.
  • Space shuttle on re-entry = 7,777.778 ms-1; 28,000 km/h; 17,500 mph.
  • the speed of sound in air (Mach 1) is about 340 ms-1, and 1500 ms-1 in water
  • Taipei 101 Observatory Elevator = 1010 m/min ; 16.667 ms-1 ; 60.6 km/h; 37.6 mph


promptness in Afrikaans: Spoed
promptness in Arabic: سرعة
promptness in Catalan: Rapidesa
promptness in Welsh: Buanedd
promptness in Danish: Fart
promptness in German: Geschwindigkeit
promptness in Estonian: Kiirus
promptness in Spanish: Rapidez
promptness in Esperanto: Rapido
promptness in French: Vitesse
promptness in Korean: 속력
promptness in Croatian: Brzina
promptness in Ido: Rapideso
promptness in Icelandic: Hraði
promptness in Italian: Velocità media
promptness in Hebrew: מהירות
promptness in Georgian: სიჩქარე
promptness in Latvian: Ātrums
promptness in Lithuanian: Greitis
promptness in Macedonian: Брзина
promptness in Malay (macrolanguage): Laju
promptness in Dutch: Snelheid
promptness in Japanese: 速さ
promptness in Norwegian: Fart
promptness in Norwegian Nynorsk: Fart
promptness in Polish: Szybkość
promptness in Portuguese: Rapidez
promptness in Romanian: Viteză
promptness in Russian: Скорость
promptness in Simple English: Speed
promptness in Finnish: Vauhti
promptness in Swedish: Fart
promptness in Thai: อัตราเร็ว
promptness in Ukrainian: Швидкість
promptness in Chinese: 速率

Synonyms, Antonyms and Related Words

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