# Speed

In kinematics, the speed of an object is the magnitude of its velocity (the rate of change of its position); it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero.

Like velocity, speed has the dimensions of a length divided by a time; the SI unit of speed is the meter per second, but the most usual unit of speed in everyday usage is the kilometer per hour or, in the USA and the UK, miles per hour. For air and marine travel the knot is commonly used.

The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in a vacuum c = 299,792,458 meters per second, approximately 1079 million kilometers per hour (671,000,000 mph). Matter cannot quite reach the speed of light, as this would require an infinite amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed. In day-to-day athletics, it is proper to say that a teenager can achieve at least 20 km/h (or 12.43 mph) of speed while a best runner can achieve 30 km/h (or 18.64 mph) which is similar to running 100 metres in about 12 seconds. The average speed for a teenager is 24 km/h, which can be a result of running 100 m in 15 seconds.

### Other articles related to "speed":

Speed - Distance of Inter-city Rail
... Development of high-speed rail in some countries increases the share of railway for such longer-distance journeys ... In conventional non high-speed rail, overnight trains are common for this distance ... Faster high-speed rail of 350 km (217 mi), such as the proposed Beijing-Shanghai Express Railway in China (1,300 km/808 mi, or 5 hours) and Tokyo-Sapporo Hokkaido ...
Tonya Harding - Automobile Racing Land Speed Record
... On August 12, 2009, Harding set a new land speed record for a vintage gas coupe with a speed of 97.177 mph driving a 1931 Ford Model A, named Lickity - Split, on the Bonneville Salt Flats ...
Moore's Law - Consequences and Limitations - Transistor Count Versus Computing Performance
... In multi-core CPUs, the higher transistor density does not greatly increase speed on many consumer applications that are not parallelized ... Viewed even more broadly, the speed of a system is often limited by factors other than processor speed, such as internal bandwidth and storage speed, and one can ...
Examples of Different Speeds
... Speed m/s ft/s km/h mph Notes Approximate rate of continental drift 0.00000001 0.00000003 0.00000004 0.00000002 4 cm/year ... Varies depending on location Speed of a common snail 0.001 0.003 0.004 0.002 1 millimeter per second ... Sprint runners 10 32.8 22 ... Average speed over 100 meters ...
Johnson, Arkansas - Reputation As A Speed Trap
... Johnson has a reputation as a speed trap ... the police will have one car staged to control the speed along Main Drive (East and West) or Wilkerson (North and South) ... When driving through Johnson, one should be careful to observe the posted speed limit, and wear your seat belt ...

### Famous quotes containing the word speed:

If it be aught toward the general good,
Set honor in one eye, and death i’th’ other,
And I will look on both indifferently;
For let the gods so speed me as I love
The name of honor more than I fear death.
William Shakespeare (1564–1616)

Spig Wead: I’ve been thinking what a heel I’ve been about you and about my own kids. I don’t know, when I do something, I go all the way. Living. Gambling. Flying. I tap myself out. I guess that’s the way I want it to be. Maybe even the way I am.
Minne Wead: Star-spangled Spig. Damn the martinis, full speed ahead and don’t give up the ship.
Frank Fenton, William Wister Haines, co-scenarist, and John Ford. Spig Wead (John Wayne)

Among the laws controlling human societies there is one more precise and clearer, it seems to me, than all the others. If men are to remain civilized or to become civilized, the art of association must develop and improve among them at the same speed as equality of conditions spreads.
Alexis de Tocqueville (1805–1859)