Speed

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Speed

Speed is the rate of motionMotion (physics)

In physics, motion means a continuous change in the position of a body relative to a reference point, as measured by a parti...
, or equivalently the rate of change in position, often expressed as distanceDistance Summary

Distance is a numerical description of how far apart things lie....
d traveled per unitUnits of measurement

The definition, agreement and practical use of units of measurement have played a crucial role in human endeavour from early...
of timeTime

Two distinct views exist on the meaning of time....
t.

Speed is a scalarScalar (physics)

In physics, a scalar is a simple physical quantity that does not depend on direction, and therefore does not depend on the c...
quantityQuantity

Quantity is a kind of property which exists as magnitude or multitude....
with dimensionDimension

In common usage, a dimension is a parameter or measurement required to define the characteristics of an object—i.e....
s distanceLength

Length is the long dimension of any object....
/timeTime

Two distinct views exist on the meaning of time....
; the equivalent vectorVector (spatial)

In physics and in vector calculus, a spatial vector, or simply vector, is a concept characterized by a magnitude and a...
quantity to speed is known as velocityVelocity

The velocity of an object is simply its speed in a particular direction....
. 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 magnitudeMagnitude (mathematics)

The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of th...
component of velocity.

In mathematical notation, it is simply:

Note that "v" is the variable for speed.

Objects that move horizontally as well as vertically (such as aircraftAircraft

An aircraft is any machine capable of atmospheric flight....
) distinguish forward speedV speeds

V speeds are speeds that define certain performance and limiting characteristics of an aircraft....
and climbing speedV speeds

V speeds are speeds that define certain performance and limiting characteristics of an aircraft....
.
UnitsUnits of speed include:

Mach 1 ˜ 343 ms^-1 ˜ 1235 km/h ˜ 768 mph in dry air at sea-level pressure and 293 kelvinKelvin

The Kelvin scale is a temperature scale where absolute zero—the coldest possible temperature where there is no heat en...
(See Speed of soundSpeed of sound

The speed of sound is a term used to describe the speed of sound waves passing through an elastic medium....
for more detail.)

c = 299,792,458 ms^-1

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 speedometerSpeedometer

A speedometer measures the instantaneous speed of a vehicle....
to measure the speed they are going.
Average speedSpeed as a physical propertyPhysical property

A physical property is any aspect of an object or substance that can be measured or perceived without changing its identity....
represents primarily instantaneous speed.

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Timeline

2004 NASA's hypersonic jet ''ScramJet'' breaks a record by reaching a velocity of about 7,000 mph in an unmanned experimental flight. It obtains a speed of Mach 9.6, almost 10 times the speed of sound.

Encyclopedia

Units

Units of speed include:

meters per second, (symbol ms^-1; m/s), the SI derived unitSI derived unit

SI derived units are part of the SI system of measurement units and are derived from the seven SI base units....
kilometers per hour, (symbol km/h)
miles per hourMiles per hour

Miles per hour is a unit of speed, expressing the number of international miles covered per hour....
, (symbol m/h)
knots
MachMach number

Mach number is defined as a ratio of the speed of an object or flow relative to the speed of sound in the medium through w...
, where Mach 1 is the speed of soundFacts About Speed of sound

The speed of sound is a term used to describe the speed of sound waves passing through an elastic medium....
; Mach n is n times as fast.

Mach 1 ˜ 343 ms^-1 ˜ 1235 km/h ˜ 768 mph in dry air at sea-level pressure and 293 kelvinKelvin

The Kelvin scale is a temperature scale where absolute zero—the coldest possible temperature where there is no heat en...
(See Speed of soundSpeed of sound

The speed of sound is a term used to describe the speed of sound waves passing through an elastic medium....
for more detail.)

speed of lightSpeed of light

The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin w...
in vacuumVacuum

A vacuum is a volume of space that is substansively empty of matter, so that gaseous pressure is much less than standard atm...
(symbol c) is one of the natural unitsNatural units

In physics, natural units are physical units of measurement defined in terms of universal physical constants in such a manne...

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 speedometerSpeedometer

A speedometer measures the instantaneous speed of a vehicle....
to measure the speed they are going.

Average speed

Speed as a physical propertyPhysical property

A physical property is any aspect of an object or substance that can be measured or perceived without changing its identity....
represents primarily instantaneous speed. In real life we often use average speed (denoted ), which is rateRate

A rate is a special kind of ratio, indicating a relationship between two measurements with different units, such as miles to...
of total distanceDistance

Distance is a numerical description of how far apart things lie....
(or lengthLength

Length is the long dimension of any object....
) and timeTime

Two distinct views exist on the meaning of 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:

Instantaneous speed defined as a function of timeTime Summary

Two distinct views exist on the meaning of time....
on interval gives average speed:

while instantaneous speed defined as a function of distanceDistance

Distance is a numerical description of how far apart things lie....
(or lengthLength

Length is the long dimension of any object....
) on interval gives average speed:

It is often intuitively expected, but incorrect, that going half a distance with speed and second half with speed , produces total average speed . The correct value is
(Note that the first is a proper arithmetic meanArithmetic mean

In mathematics and statistics, the arithmetic mean of a list of numbers is the sum of all the members of the list divided b...
while the second is a proper harmonic meanHarmonic mean

In mathematics, the harmonic mean is one of several methods of calculating an average....
).

Average speed can be derived also from speed distribution functionProbability density function

In mathematics, a probability density function serves to represent a probability distribution in terms of integrals....
(either in time or on distance):

Examples of different speeds

Below are some examples of different speed. See also main article Orders of magnitude (speed)Facts About Orders of magnitude (speed)

To help compare different orders of magnitude, the following list describes various speed levels between 1.3 m·s-1 and 3 ...
:

A brisk walkWALK Summary

WALK is the callsign for two radio stations on Long Island:...
= 1.667 ms^-1; 6 km/h; 3.75 mph (5.5 feet per second).
Average orbital speed of planet EarthEarth

Earth is the third planet in the solar system in terms of distance from the Sun, and the fifth largest....
= 29,783 ms^-1; 107,218.8 km/h; 66,622.67 mph.
Official air speed recordAir speed record

Determining the fastest aircraft in the world is difficult, because of the wide variety of designs....
= 980.278 ms^-1; 3,529 km/h; 2,188 mph.
OlympicOlympic Games

The Olympic Games, or Olympics, are an international multi-sport event taking place every four years and comprising su...
sprintersSprint (race)

Sprints are short running races in athletics....
(average speed over 100 metres) = 10 ms^-1; 36 km/h; 22.5 mph.
Speed limit on a FrenchFrance

France, officially the French Republic, is a country whose metropolitan territory is located in Western Europe and whi...
autorouteFreeway

A freeway is a type of highway that is designed for safer high-speed operation of motor vehicles through the elimination o...
= 36.111 ms^-1; 130 km/h; 80 mph.
Speed of a common snailFacts About Snail

The name snail applies to most members of the molluscan class Gastropoda that have coiled shells....
= 0.001 ms^-1; 0.0036 km/h; 0.0023 mph (1.02 millimeters per second).
Taipei 101Taipei 101

Taipei 101 is a 101-floor landmark skyscraper located in Taipei City, Taiwan ....
observatory elevator = 1010 m/min ; 16.667 ms^-1 ; 60.6 km/h; 37.6 mph
the speed of soundSpeed of sound

The speed of sound is a term used to describe the speed of sound waves passing through an elastic medium....
in dry air at 20 °C (68 °F) is 343 ms^-1 ; 1235 km/h, or 770 mph.
Top cruising speed of a Boeing 747-8Boeing 747-8

The Boeing 747-8 is the latest model of the Boeing 747, officially announced on November 14 2005 to compete with the Airbus ...
= 290.947 ms^-1; 1047.41 km/h; 650.83 mph;
Space shuttleSpace Shuttle

NASA's Space Shuttle, officially called Space Transportation System , is the United States government's current manned...
on re-entry = 7,777.778 ms^-1; 28,000 km/h; 17,500 mph.

Speed

Units

Average speed

Examples of different speeds

See also

External links