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This article is about speed in physics. For other uses, see Speed (disambiguation).

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. In Physics, motion means a constant change in the location of a body Distance is a numerical description of how far apart objects are For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of

Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as velocity. In Physics, a scalar is a simple Physical quantity that is not changed by Coordinate system rotations or translations (in Newtonian mechanics or Quantity is a kind of property which exists as magnitude or multitude In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it 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 For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of In Physics, velocity is defined as the rate of change of Position. 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. 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

In mathematical notation, it is simply:

v = \left|\frac {d}{t}\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. In Aviation, V-speeds or Velocity-speeds are standard terms used to define Airspeeds important or useful to the operation of Aircraft, such In Aviation, V-speeds or Velocity-speeds are standard terms used to define Airspeeds important or useful to the operation of Aircraft, such

Contents

Units

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. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Sound is a vibration that travels through an elastic medium as a Wave. )
c = 299,792,458 ms-1
1 m/s = 3. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. In Physics, natural units are Physical units of Measurement defined in terms of universal Physical constants, such that some chosen physical 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. A speedometer is a device that measures the instantaneous Speed of a land vehicle

Average speed

Speed as a physical property represents primarily instantaneous speed. A physical property is any aspect of an object or substance that can be measured or perceived without changing its identity. In real life we often use average speed (denoted |\tilde{v}|), which is rate of total distance (or length) and time interval. Distance is a numerical description of how far apart objects are 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 For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of 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{v}| = \frac{\Delta l}{\Delta t}

Instantaneous speed defined as a function of time on interval [t0,t1] gives average speed:

|\tilde{v}| = \frac{\int_{t_0}^{t_1} |v|(t) \, dt}{\Delta t}

while instantaneous speed defined as a function of distance (or length) on interval [l0,l1] gives average speed:

|\tilde{v}| = \frac{\Delta l}{\int_{l_0}^{l_1} \frac{1}{|v|(l)} \, dl}

It is often intuitively expected, but incorrect, that going half a distance with speed | v | a and second half with speed | v | b, produces total average speed |\tilde{v}| = \frac{|v|_a + |v|_b}{2}. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Distance is a numerical description of how far apart objects are 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 The correct value is |\tilde{v}| = \frac{2}{\frac{1}{|v|_a} + \frac{1}{|v|_b}}
(Note that the first is a proper arithmetic mean while the second is a proper harmonic mean). In Mathematics and Statistics, the arithmetic Mean (or simply the mean) of a list of numbers is the sum of all the members of the list divided In Mathematics, the harmonic mean (formerly sometimes called the subcontrary mean) is one of several kinds of Average.

Average speed can be derived also from speed distribution function (either in time or on distance):

|v| \sim D_t\; \Rightarrow \; |\tilde{v}| = \int |v| D_t(|v|) \, dv
|v| \sim D_l\; \Rightarrow \; |\tilde{v}| = \frac{1}{\int \frac{D_l(|v|)}{|v|} \, dv}

Examples of different speeds

Below are some examples of different speed (see also main article Orders of magnitude (speed)):

See also

External Links

References

Kinematics

← Integrate . Kinematics ( Greek κινειν, kinein, to move is a branch of Classical mechanics which describes the motion of objects without The European Space Agency 's INTErnational Gamma-Ray Astrophysics Laboratory ( INTEGRAL) is detecting some of the most energetic radiation that comes from space . . Differentiate →
Displacement (Distance) | Velocity (Speed) | Acceleration | Jerk | Snap
In Calculus, a branch of mathematics the derivative is a measurement of how a function changes when the values of its inputs change In Physics, displacement is the vector that specifies the position of a point or a particle in reference to a previous position or to the origin of the chosen Distance is a numerical description of how far apart objects are In Physics, velocity is defined as the rate of change of Position. In Physics, jerk, jolt (especially in British English) surge or lurch, is the rate of change of Acceleration; that is

Dictionary

speed

-noun

  1. the state of moving quickly or the capacity for rapid motion; rapidity
  2. the rate of motion or action, specifically (mathematics)/(physics) the magnitude of the velocity; the rate distance is traversed in a given time
  3. (photography) the sensitivity to light of film, plates.
  4. (slang) any amphetamine drug used as a stimulant, especially illegally, especially methamphetamine
  5. (archaic) luck, success, prosperity

-verb

  1. (archaic, intransitive) To prosper, be lucky.
  2. (archaic, transitive) To help someone, to give them fortune.
  3. To go fast, especially excessively fast.
  4. To exceed the speed limit.
  5. (slang) To be under the influence of stimulant drugs, especially amphetamines.
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