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'''Ferð'''  er hraðavigurs, gjarnan táknuð með bókstafnum ''v''. Ólíkt hraða hefur ferð enga stefnu, og eining ferðar er áttavita eða GPS tæki.

Stærðfræðilega má lýsa (meðal)hraða með eftirfarandi jöfnu:
:<math>v = \frac {d}{t}</math>

Algengar mælieiningar sem lýsa hraða eru:
*metrar á sekúndu, (tákn m/s), sem er sú hraðaeining sem SI einingakerfið notast við
*kílómetrar á klukkustund, (tákn km/h)
*mílur á klukkustund, (tákn mph)
*hnútar (sjómílur á klukkustund, merki kt)
*Mach tala, þar sem Mach 1 er hraði hljóðsins; Mach ''n'' er þá ''n'' sinnum meiri hraði
::Mach 1 = ~343&nbsp;m/s = ~1235&nbsp;km/h = ~768&nbsp;mi/h (sjá hljóðhraði fyrir nánari upplýsingar)
*ljóshraði í lofttæmi (tákn''c'') er einn af þeim grunnföstum sem eðlisfræðingar nota til að skilgreina mælieiningar
::''c'' = 299,792,458&nbsp;m/s
*Önnur mikilvæg hlutföll:
::1 m/s = 3.6&nbsp;km/h
::1 mph = 1.609&nbsp;km/h
::1 knot = 1.852&nbsp;km/h = 0.514&nbsp;m/s 

'''Speed''' is the rate of motion, or equivalently the rate of change in position, often expressed as unit of time ''t''.

Speed is a scalar distance/vector quantity to speed is known as magnitude component of velocity.

In mathematical notation, it is simply:

:<math>v = \left|\frac {d}{t}\right|.</math>
Note that "v" is the variable for speed.

Objects that move horizontally as well as vertically (such as forward speed''' and '''climbing speed'''.

==Units==
Units of speed include:
*meters per second, (symbol ms<sup>-1</sup>; m/s), the SI derived unit
*kilometers per hour, (symbol km/h)
*miles per hour, (symbol m/h)
*knots (nautical miles per hour, symbol kt)
*Mach, where Mach 1 is the speed of sound; Mach ''n'' is ''n'' times as fast.
::Mach 1 ≈ 343&nbsp;ms<sup>-1</sup> ≈ 1235&nbsp;km/h ≈ 768&nbsp;mph in dry air at sea-level pressure and 293 kelvin (See ''Speed of sound'' for more detail.)
*speed of light in vacuum (symbol ''c'') is one of the natural units
::''c'' = 299,792,458&nbsp;ms<sup>-1</sup>
*Other important conversions
::1 m/s = 3.6&nbsp;km/h
::1 mph = 1.609&nbsp;km/h 
::1 knot = 1.852&nbsp;km/h = 0.514&nbsp;ms<sup>-1</sup>

Vehicles often have a speedometer to measure the speed they are going.

==Average speed==
Speed as a \tilde{v}|</math>), which is [[rate of total distance (or length) and 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:

:<math>|\tilde{v}| = \frac{\Delta l}{\Delta t}</math>

Instantaneous speed defined as a function of time on interval <math>[t_0, t_1]</math> gives average speed:

:<math>|\tilde{v}| = \frac{\int_{t_0}^{t_1} |v|(t) \, dt}{\Delta t}</math>

while instantaneous speed defined as a function of distance (or length) on interval <math>[l_0, l_1]</math> gives average speed: