What is speed?

Speed is the rate of motion. It is the distance traveled per unit time denoted by the formula;

^v = ^d/_t

where:

v = speed

d = distance

t = time

Speed is a scalar quantity, meaning it has no element of direction. Velocity in contrast is a vector quantity. It has speed as its magnitude and an element of direction. An example of this is the travel of a hurricane. A hurricane has speed traveling in a certain direction.

Units of speed include:

meters per second, (symbol ms-1; m/s), the SI derived unit
kilometers per hour, (symbol km/h)
miles per hour, (symbol mph)
knots (nautical miles per hour, symbol kt); usually used on marine vessels
mach number, speed divided by the speed of sound
speed of light in vacuum (symbol c) is one of the natural units

c = 299,792,458 ms-1

Important conversions between units of speed include:

1 m/s = 3.6 km/h
1 mph = 1.609 km/h
1 knot = 1.852 km/h = 0.514 ms-1

Some known speeds :

Speed of a common snail = 0.001 ms-1; 0.004 km/h; 0.002 mph (1 millimeter per second).

A brisk walk = 1.7 ms-1; 6 km/h; 4 mph (5.5 feet per second).

Olympic sprinters (average speed over 100 metres) = 10 ms-1; 36 km/h; 22 mph.

Taipei 101 observatory elevator = 1010 m/min ; 16.7 ms-1 ; 60.6 km/h; 37.6 mph

Cruising speed of a Boeing 747-8 = 290 ms-1; 1050 km/h; 650 mph; (Mach 0.85)

The speed of sound in dry air at sea-level pressure and 20 °C (293 kelvin) = 343 ms-1 ≈ 1235 km/h ≈ 768 mph ( = Mach 1 by definition).

Official flight airspeed record = 980 ms-1; 3,530 km/h; 2,194 mph.

Escape velocity on Earth: 11.2 km/s

Space shuttle on re-entry = 7,800 ms-1; 28,000 km/h; 17,500 mph.

Average orbital speed of planet Earth = 29,783 ms-1; 107,218 km/h; 66,623 mph.

Speed of light in vacuum (symbol c) 299,792,458 ms-1 (exactly, by definition).

(Ref. Wikipedia)