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Speed is the rate of motion
Motion (physics)

In physics, motion means a constant change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, Displacement , and time....
, or equivalently the rate of change of distance
Distance

Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, a period of time, or an estimation based on other criteria ....
.

Speed is a scalar
Scalar (physics)

In physics, a scalar is a simple physical quantity that is not changed by coordinate system rotations or translations , or by Lorentz transformations or space-time translations ....
 quantity
Quantity

Quantity is a kind of property which exists as magnitude or multitude. It is among the basic classes of things along with Quality , substance, change, and relation....
 with dimension
Dimension

In mathematics, the dimension of a space is roughly defined as the minimum number of coordinates needed to specify every point within it. For example: a point on the unit circle in the plane can be specified by two Cartesian coordinates but one can make do with a single coordinate , so the circle is 1-dimensional even though it exists in...
s length
Length

Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end....
/time
Time

Time is a component of the measurement used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects....
; the equivalent vector quantity to speed is velocity
Velocity

In physics, velocity is defined as the Derivative of Position vector. It is a vector physical quantity; both speed and direction are required to define it....
. 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
Magnitude (mathematics)

The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs....
 component of velocity.

In mathematical notation, if an object traveling at constant speed moves a distance in time , its speed, denoted by , is simply given by .

In many situations, objects do not move at a constant speed.






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Speed is the rate of motion
Motion (physics)

In physics, motion means a constant change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, Displacement , and time....
, or equivalently the rate of change of distance
Distance

Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, a period of time, or an estimation based on other criteria ....
.

Speed is a scalar
Scalar (physics)

In physics, a scalar is a simple physical quantity that is not changed by coordinate system rotations or translations , or by Lorentz transformations or space-time translations ....
 quantity
Quantity

Quantity is a kind of property which exists as magnitude or multitude. It is among the basic classes of things along with Quality , substance, change, and relation....
 with dimension
Dimension

In mathematics, the dimension of a space is roughly defined as the minimum number of coordinates needed to specify every point within it. For example: a point on the unit circle in the plane can be specified by two Cartesian coordinates but one can make do with a single coordinate , so the circle is 1-dimensional even though it exists in...
s length
Length

Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end....
/time
Time

Time is a component of the measurement used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects....
; the equivalent vector quantity to speed is velocity
Velocity

In physics, velocity is defined as the Derivative of Position vector. It is a vector physical quantity; both speed and direction are required to define it....
. 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
Magnitude (mathematics)

The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs....
 component of velocity.

In mathematical notation, if an object traveling at constant speed moves a distance in time , its speed, denoted by , is simply given by .

In many situations, objects do not move at a constant speed. For example, if a car goes 60 miles in 2 hours, its average speed during that time is 30 miles per hour, but its instantaneous speed may have varied. For an object which is accelerating or decelerating
Acceleration

File:Acceleration.JPGFile:Acceleration components.JPGIn physics, and more specifically kinematics, acceleration is the change in velocity over time....
, the instantaneous speed is given by , where is the distance it travels in a very short period of time . If the object travels a total distance in time , its average speed over that time is given by .

Units

Units of speed include:
  • meters per second, (symbol ms-1; m/s), the SI derived unit
    SI derived unit

    SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
  • kilometers per hour, (symbol km/h)
  • miles per hour
    Miles per hour

    The mile per hour is a physical unit of speed, expressing the number of Mile covered per hour.It is currently the Unit of measurement used for speed limits, and speeds, on roads in the United Kingdom and United States....
    , (symbol mph)
  • knots (nautical mile
    Nautical mile

    A nautical mile or sea mile is a unit of length. It corresponds approximately to one minute of arc of latitude along any meridian .It is a non-International System of Units unit used especially by navigators in the shipping and aviation industries....
    s per hour, symbol kt)
  • Mach number
    Mach number

    Mach number is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance. It is commonly used to represent an object's speed, when it is travelling at the speed of sound....
    , speed divided by the speed of sound
    Speed of sound

    Sound is a vibration that travels through an elasticity medium as a wave. The speed of sound describes how much distance such a wave travels in a certain amount of time....
  • speed of light
    Speed of light

    The speed of light in an free space is an important physical constant usually written as c, with a value of 299,792,458 metres per second....
     in vacuum
    Vacuum

    A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty," but in reality, no volume of space can ever be perfectly empty....
     (symbol c) is one of the natural units
    Natural units

    In physics, natural units are physical units of measurement defined in such a way that certain selected universal physical constants are normalized to unity; that is, their numerical value becomes exactly 1 when measured in some system of 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

Examples of different speeds

  • Speed of a common snail
    Snail

    The word snail is a common name for almost all members of the molluscan class Gastropoda that have coiled animal shells in the adult stage. When the word snail is used in a general sense, it includes sea snails, land snails and freshwater snails....
     = 0.001 ms-1; 0.004 km/h; 0.002 mph (1 millimeter per second).
  • A brisk walk
    WALK

    WALK may refer to:*WALK , a radio station licensed to East Patchogue, New York, United States*WALK-FM, a radio station licensed to Patchogue, New York, United States...
     = 1.7 ms-1; 6 km/h; 4 mph (5.5 feet per second).
  • Olympic
    Olympic Games

    The Olympic Games are an international multi-sport event established for both summer and winter sports. There have been two generations of the Olympic Games; the first were the Ancient Olympic Games held at Olympia, Greece, Greece....
     sprinters
    Sprint (race)

    Sprints are short running races in athletics . They are roughly classified as events in which top runners will not have to "pace themselves", but can run as fast as possible for the entire distance....
     (average speed over 100 metres) = 10 ms-1; 36 km/h; 22 mph.
  • Speed limit on a French
    France

    France , officially the French Republic , is a country whose Metropolitan France is located in Western Europe and that also comprises various Overseas departments and territories of France....
     autoroute
    Freeway

    A freeway is a type of road designed for Road safety#Motorway high-speed operation of motor vehicles through the elimination of at-grade intersections....
     = 36 ms-1; 130 km/h; 80 mph.
  • Taipei 101
    Taipei 101

    Taipei 101 is a landmark skyscraper located in Xinyi District, Taipei, Republic of China . The building, designed by C.Y. Lee & Partners and constructed primarily by KTRT Joint Ventureand Samsung Engineering & Construction, is the World's tallest structures according to the Council on Tall Buildings and Urban Habitat, the arbiter of tall bui...
     observatory elevator = 1010 m/min ; 16.7 ms-1 ; 60.6 km/h; 37.6 mph
  • Cruising speed of a Boeing 747-8
    Boeing 747-8

    The Boeing 747-8 is a wide-body aircraft commercial airliner being developed by Boeing Commercial Airplanes. Officially announced in 2005, the 747-8 is the latest evolutionary variant of the Boeing 747, with lengthened fuselage, redesigned wings and improved efficiency....
     = 290 ms-1; 1050 km/h; 650 mph; (Mach
    Mach

    Mach may refer to:* Mach number, a measure of speed* Gillette Mach3, a manual razor with three blades* Mach bands, an optical illusion* Muscarinic acetylcholine receptor, abbreviated mACh...
     0.85)
  • The speed of sound
    Speed of sound

    Sound is a vibration that travels through an elasticity medium as a wave. The speed of sound describes how much distance such a wave travels in a certain amount of time....
     in dry air at sea-level pressure and 20 °C (293 kelvin
    Kelvin

    The kelvin is a Units of measurement of temperature and is one of the seven SI base units. The Kelvin scale is a Thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero ....
    ) is 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.
  • Space shuttle
    Space Shuttle

    NASA's Space Shuttle, officially called the Space Transportation System , is the spacecraft currently used by the United States government for its human spaceflight missions....
     on re-entry = 7,800 ms-1; 28,000 km/h; 17,500 mph.
  • Average orbital speed of planet Earth
    Earth

    Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
     = 29,783 ms-1; 107,218 km/h; 66,623 mph.
  • Speed of light
    Speed of light

    The speed of light in an free space is an important physical constant usually written as c, with a value of 299,792,458 metres per second....
     in vacuum
    Vacuum

    A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty," but in reality, no volume of space can ever be perfectly empty....
     (symbol c) 299,792,458 ms-1 (exactly, by definition).

See also

  • Air speed
  • Land speed
    Land speed

    An object's speed across land is measured by difference in movement between the object and the land beneath it. Atmospheric pressure and aerodynamics must be considered when attempting to calculate possible speeds from the force applied....
  • List of vehicle speed records
    List of vehicle speed records

    The following is a list of speed records for various categories of vehicles....
  • Typical projectile speeds
    Projectile

    A projectile is any object propelled through space by the exertion of a force, which ceases after launch. In a general sense, even a Football or baseball may be considered a projectile....
  • Speedometer
    Speedometer

    A speedometer is a device that measures the instantaneous speed of a land vehicle.Now universally fitted to motor vehicles, they started to be available as options in the 1900s, and as standard equipment from about 1910 onwards....
  • V speeds
    V speeds

    In aviation, V-speeds or Velocity-speeds are standard terms used to define airspeeds important or useful to the operation of aircraft, such as airplanes, gliders, autogiros, helicopters, blimps, and dirigibles....


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