Speed - wikipedia Speed This article is about the property of moving bodies. For other uses, see Speed ( disambiguation ). `` Slow '' and `` Slowness '' redirect here. For other uses, see Slow ( disambiguation ) and Slowness ( disambiguation ). This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( July 2016 ) Speed Speed can be thought of as the rate at which an object covers distance. A fast - moving object has a high speed and covers a relatively large distance in a given amount of time, while a slow - moving object covers a relatively small amount of distance in the same amount of time. Common symbols SI unit m / s, m s Classical mechanics F → = m a → ( displaystyle ( \vec ( F ) ) = m ( \vec ( a ) ) ) Second law of motion History Timeline Branches Applied Celestial Continuum Dynamics Kinematics Kinetics Statics Statistical Fundamentals Acceleration Angular momentum Couple D'Alembert's principle Energy kinetic potential Force Frame of reference Impulse Inertia / Moment of inertia Mass Mechanical power Mechanical work Moment Momentum Space Speed Time Torque Velocity Virtual work Formulations Newton 's laws of motion Analytical mechanics Lagrangian mechanics Hamiltonian mechanics Routhian mechanics Hamilton -- Jacobi equation Appell 's equation of motion Udwadia -- Kalaba equation Koopman -- von Neumann mechanics Core topics Damping ( ratio ) Displacement Equations of motion Euler 's laws of motion Fictitious force Friction Harmonic oscillator Inertial / Non-inertial reference frame Mechanics of planar particle motion Motion ( linear ) Newton 's law of universal gravitation Newton 's laws of motion Relative velocity Rigid body dynamics Euler 's equations Simple harmonic motion Vibration Rotation Circular motion Rotating reference frame Centripetal force Centrifugal force reactive Coriolis force Pendulum Tangential speed Rotational speed Angular acceleration / displacement / frequency / velocity Scientists Galileo Newton Kepler Horrocks Halley Euler d'Alembert Clairaut Lagrange Laplace Hamilton Poisson Daniel Bernoulli Johann Bernoulli Cauchy In everyday use and in kinematics, the speed of an object is the magnitude of its velocity ( the rate of change of its position ) ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance travelled by the object divided by the duration of the interval ; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero. Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second, but the most common unit of speed in everyday usage is the kilometre per hour or, in the US and the UK, miles per hour. For air and marine travel the knot is commonly used. The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in a vacuum c = 7008299792458000000 ♠ 299 792 458 metres per second ( approximately 7008299722222222222 ♠ 1079000000 km / h or 7008299963840000000 ♠ 671 000 000 mph ). Matter can not quite reach the speed of light, as this would require an infinite amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed. Contents 1 Definition 1.1 Historical definition 1.2 Instantaneous speed 1.3 Average speed 1.4 Tangential speed 2 Units 3 Examples of different speeds 4 Psychology 5 See also 6 References Definition Historical definition Italian physicist Galileo Galilei is usually credited with being the first to measure speed by considering the distance covered and the time it takes. Galileo defined speed as the distance covered per unit of time. In equation form, this is v = d t, ( displaystyle v = ( \frac ( d ) ( t ) ), ) where v ( displaystyle v ) is speed, d ( displaystyle d ) is distance, and t ( displaystyle t ) is time. A cyclist who covers 30 metres in a time of 2 seconds, for example, has a speed of 15 metres per second. Objects in motion often have variations in speed ( a car might travel along a street at 50 km / h, slow to 0 km / h, and then reach 30 km / h ). Instantaneous speed Speed at some instant, or assumed constant during a very short period of time, is called instantaneous speed. By looking at a speedometer, one can read the instantaneous speed of a car at any instant. A car travelling at 50 km / h generally goes for less than one hour at a constant speed, but if it did go at that speed for a full hour, it would travel 50 km. If the vehicle continued at that speed for half an hour, it would cover half that distance ( 25 km ). If it continued for only one minute, it would cover about 833 m. In mathematical terms, the instantaneous speed v ( displaystyle v ) is defined as the magnitude of the instantaneous velocity v ( displaystyle ( \boldsymbol ( v ) ) ), that is, the derivative of the position r ( displaystyle ( \boldsymbol ( r ) ) ) with respect to time : v = v = r  ̇ = d r d t. ( displaystyle v = left ( \boldsymbol ( v ) ) \right = left ( dot ( \boldsymbol ( r ) ) ) \right = left ( \frac ( d ( \boldsymbol ( r ) ) ) ( dt ) ) \right ,. ) If s ( displaystyle s ) is the length of the path ( also known as the distance ) travelled until time t ( displaystyle t ), the speed equals the time derivative of s ( displaystyle s ) : v = d s d t. ( displaystyle v = ( \frac ( ds ) ( dt ) ). ) In the special case where the velocity is constant ( that is, constant speed in a straight line ), this can be simplified to v = s / t ( displaystyle v = s / t ). The average speed over a finite time interval is the total distance travelled divided by the time duration. Average speed Different from instantaneous speed, average speed is defined as the total distance covered divided by the time interval. For example, if a distance of 80 kilometres is driven in 1 hour, the average speed is 80 kilometres per hour. Likewise, if 320 kilometres are travelled in 4 hours, the average speed is also 80 kilometres per hour. When a distance in kilometres ( km ) is divided by a time in hours ( h ), the result is in kilometres per hour ( km / h ). Average speed does not describe the speed variations that may have taken place during shorter time intervals ( as it is the entire distance covered divided by the total time of travel ), and so average speed is often quite different from a value of instantaneous speed. If the average speed and the time of travel are known, the distance travelled can be calculated by rearranging the definition to d = v  ̄ t. ( displaystyle d = ( \boldsymbol ( \bar ( v ) ) ) t ,. ) Using this equation for an average speed of 80 kilometres per hour on a 4 - hour trip, the distance covered is found to be 320 kilometres. Expressed in graphical language, the slope of a tangent line at any point of a distance - time graph is the instantaneous speed at this point, while the slope of a chord line of the same graph is the average speed during the time interval covered by the chord. Tangential speed Linear speed is the distance travelled per unit of time, while tangential speed ( or tangential velocity ) is the linear speed of something moving along a circular path. A point on the outside edge of a merry - go - round or turntable travels a greater distance in one complete rotation than a point nearer the center. Travelling a greater distance in the same time means a greater speed, and so linear speed is greater on the outer edge of a rotating object than it is closer to the axis. This speed along a circular path is known as tangential speed because the direction of motion is tangent to the circumference of the circle. For circular motion, the terms linear speed and tangential speed are used interchangeably, and both use units of m / s, km / h, and others. Rotational speed ( or angular speed ) involves the number of revolutions per unit of time. All parts of a rigid merry - go - round or turntable turn about the axis of rotation in the same amount of time. Thus, all parts share the same rate of rotation, or the same number of rotations or revolutions per unit of time. It is common to express rotational rates in revolutions per minute ( RPM ) or in terms of the number of `` radians '' turned in a unit of time. There are little more than 6 radians in a full rotation ( 2π radians exactly ). When a direction is assigned to rotational speed, it is known as rotational velocity or angular velocity. Rotational velocity is a vector whose magnitude is the rotational speed. Tangential speed and rotational speed are related : the greater the RPMs, the larger the speed in metres per second. Tangential speed is directly proportional to rotational speed at any fixed distance from the axis of rotation. However, tangential speed, unlike rotational speed, depends on radial distance ( the distance from the axis ). For a platform rotating with a fixed rotational speed, the tangential speed in the centre is zero. Towards the edge of the platform the tangential speed increases proportional to the distance from the axis. In equation form : v ∝ r ω, ( displaystyle v propto ! , r omega ,, ) where v is tangential speed and ω ( Greek letter omega ) is rotational speed. One moves faster if the rate of rotation increases ( a larger value for ω ), and one also moves faster if movement farther from the axis occurs ( a larger value for r ). Move twice as far from the rotational axis at the centre and you move twice as fast. Move out three times as far and you have three times as much tangential speed. In any kind of rotating system, tangential speed depends on how far you are from the axis of rotation. When proper units are used for tangential speed v, rotational speed ω, and radial distance r, the direct proportion of v to both r and ω becomes the exact equation v = r ω. ( displaystyle v = r omega ,. ) Thus, tangential speed will be directly proportional to r when all parts of a system simultaneously have the same ω, as for a wheel, disk, or rigid wand. Units Main article : Conversion of units § Speed or velocity Units of speed include : metres per second ( symbol m s or m / s ), the SI derived unit ; kilometres per hour ( symbol km / h ) ; miles per hour ( symbol mi / h or mph ) ; knots ( nautical miles per hour, symbol kn or kt ) ; feet per second ( symbol fps or ft / s ) ; Mach number ( dimensionless ), speed divided by the speed of sound ; in natural units ( dimensionless ), speed divided by the speed of light in vacuum ( symbol c = 7008299792458000000 ♠ 299 792 458 m / s ). Conversions between common units of speed m / s km / h mph knot ft / s 1 m / s = 3.6 7000223693600000000 ♠ 2.236 936 7000194384400000000 ♠ 1.943 844 7000328084000000000 ♠ 3.280 840 1 km / h = 6999277778000000000 ♠ 0.277 778 6999621371000000000 ♠ 0.621 371 6999539957000000000 ♠ 0.539 957 6999911344000000000 ♠ 0.911 344 1 mph = 6999447040000000000 ♠ 0.447 04 7000160934400000000 ♠ 1.609 344 6999868976000000000 ♠ 0.868 976 7000146666700000000 ♠ 1.466 667 1 knot = 6999514444000000000 ♠ 0.514 444 1.852 7000115077900000000 ♠ 1.150 779 7000168781000000000 ♠ 1.687 810 1 ft / s = 6999304800000000000 ♠ 0.3048 7000109728000000000 ♠ 1.097 28 6999681818000000000 ♠ 0.681 818 6999592484000000000 ♠ 0.592 484 ( Values in bold face are exact. ) Examples of different speeds This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( May 2013 ) This section may contain indiscriminate, excessive, or irrelevant examples. Please improve the article by adding more descriptive text and removing less pertinent examples. See Wikipedia 's guide to writing better articles for further suggestions. ( May 2014 ) Main article : Orders of magnitude ( speed ) Speed m / s ft / s km / h mph Notes Approximate rate of continental drift 6992100000000000000 ♠ 0.000 000 01 6992300000000000000 ♠ 0.000 000 03 6992400000000000000 ♠ 0.000 000 04 6992200000000000000 ♠ 0.000 000 02 4 cm / year. Varies depending on location. Speed of a common snail 0.001 0.003 0.004 0.002 1 millimetre per second A brisk walk 1.7 5.5 6.1 3.8 A typical road cyclist 4.4 14.4 16 10 Varies widely by person, terrain, bicycle, effort, weather A fast martial arts kick 7.7 25.2 27.7 17.2 Fastest kick recorded at 130 milliseconds from floor to target at 1 meter distance. Average velocity speed across kick duration Sprint runners 12.2 40 43.92 27 Usain Bolt 's 100 metres world record. Approximate average speed of road cyclists 12.5 41.0 45 28 On flat terrain, will vary Typical suburban speed limit in most of the world 13.8 45.3 50 30 Taipei 101 observatory elevator 16.7 54.8 60.6 37.6 1010 m / min Typical rural speed limit 24.6 80.66 88.5 56 British National Speed Limit ( single carriageway ) 26.8 88 96.56 60 Category 1 hurricane 33 108 119 74 Minimum sustained speed over 1 minute Speed limit on a French autoroute 36.1 118 130 81 Highest recorded human - powered speed 37.02 121.5 133.2 82.8 Sam Whittingham in a recumbent bicycle Muzzle velocity of a paintball marker 90 295 320 200 Cruising speed of a Boeing 747 - 8 passenger jet 255 836 917 570 Mach 0.85 at 7004106680000000000 ♠ 35 000 ft ( 7004106680000000000 ♠ 10 668 m ) altitude The official land speed record 341.1 1119.1 1227.98 763 The speed of sound in dry air at sea - level pressure and 20 ° C 343 7003112500000000000 ♠ 1125 7003123500000000000 ♠ 1235 768 Mach 1 by definition. 20 ° C = 293.15 kelvins. Muzzle velocity of a 7.62 x39mm cartridge 710 7003233000000000000 ♠ 2330 7003260000000000000 ♠ 2600 7003160000000000000 ♠ 1600 The 7.62 × 39mm round is a rifle cartridge of Soviet origin Official flight airspeed record for jet engined aircraft 980 7003321500000000000 ♠ 3215 7003353000000000000 ♠ 3530 7003219400000000000 ♠ 2194 Lockheed SR - 71 Blackbird Space shuttle on re-entry 7003780000000000000 ♠ 7800 7004256000000000000 ♠ 25 600 7004280000000000000 ♠ 28 000 17,500 Escape velocity on Earth 7004112000000000000 ♠ 11 200 7004367000000000000 ♠ 36 700 7004400000000000000 ♠ 40 000 7004250000000000000 ♠ 25 000 11.2 km s Voyager 1 relative velocity to the Sun in 2013 7004170000000000000 ♠ 17 000 7004558000000000000 ♠ 55 800 7004612000000000000 ♠ 61 200 7004380000000000000 ♠ 38 000 Fastest heliocentric recession speed of any humanmade object. ( 11 mi / s ) Average orbital speed of planet Earth around the Sun 7004297830000000000 ♠ 29 783 7004977130000000000 ♠ 97 713 7005107218000000000 ♠ 107 218 7004666230000000000 ♠ 66 623 The fastest recorded speed of the Helios probes. 70,220 230,381 252,792 157,078 Recognized as the fastest speed achieved by a man - made spacecraft, achieved in solar orbit. Speed of light in vacuum ( symbol c ) 7008299792458000000 ♠ 299 792 458 7008983571056000000 ♠ 983 571 056 7009107925284800000 ♠ 1079252848 7008670616629000000 ♠ 670 616 629 Exactly 7008299792458000000 ♠ 299 792 458 m / s, by definition of the metre Psychology According to Jean Piaget, the intuition for the notion of speed in humans precedes that of duration, and is based on the notion of outdistancing. Piaget studied this subject inspired by a question asked to him in 1928 by Albert Einstein : `` In what order do children acquire the concepts of time and speed ? '' Children 's early concept of speed is based on `` overtaking '', taking only temporal and spatial orders into consideration, specifically : `` A moving object is judged to be more rapid than another when at a given moment the first object is behind and a moment or so later ahead of the other object. '' See also Air speed Land speed List of vehicle speed records Typical projectile speeds Speedometer V speeds References Look up speed or swiftness in Wiktionary, the free dictionary. Wikiquote has quotations related to : Speed Richard P. Feynman, Robert B. Leighton, Matthew Sands. The Feynman Lectures on Physics, Volume I, Section 8 - 2. Addison - Wesley, Reading, Massachusetts ( 1963 ). ISBN 0 - 201 - 02116 - 1. Jump up ^ Wilson, Edwin Bidwell ( 1901 ). Vector analysis : a text - book for the use of students of mathematics and physics, founded upon the lectures of J. Willard Gibbs. p. 125. This is the likely origin of the speed / velocity terminology in vector physics. ^ Jump up to : Elert, Glenn. `` Speed & Velocity ''. The Physics Hypertextbook. Retrieved 8 June 2017. ^ Jump up to : Hewitt ( 2006 ), p. 42 Jump up ^ `` IEC 60050 - Details for IEV number 113 - 01 - 33 : `` speed '' ``. Electropedia : The World 's Online Electrotechnical Vocabulary. Retrieved 2017 - 06 - 08. ^ Jump up to : Hewitt ( 2006 ), p. 131 Jump up ^ Hewitt ( 2006 ), p. 132 Jump up ^ http://www.kickspeed.com.au/Improve-measure-kicking-speed.html Jump up ^ http://www.wisil.recumbents.com/wisil/whpsc2009/results.htm Jump up ^ Darling, David. `` Fastest Spacecraft ''. Retrieved August 19, 2013. Jump up ^ Jean Piaget, Psychology and Epistemology : Towards a Theory of Knowledge, The Viking Press, pp. 82 -- 83 and pp. 110 -- 112, 1973. SBN 670 - 00362 - x Jump up ^ Siegler, Robert S. ; Richards, D. Dean ( 1979 ). `` Development of Time, Speed, and Distance Concepts '' ( PDF ). Developmental Psychology. 15 ( 3 ) : 288 -- 298. doi : 10.1037 / 0012 - 1649.15. 3.288. Jump up ^ Rod Parker - Rees and Jenny William, eds. ( 2006 ). Early Years Education : Histories and Traditions, Volume 1. Taylor & Francis. p. 164. CS1 maint : Uses editors parameter ( link ) Kinematics ← Integrate... Differentiate → Absement Displacement ( Distance ) Velocity ( Speed ) Acceleration Jerk Jounce Classical mechanics SI units Linear / translational quantities Angular / rotational quantities Dimensions Dimensions time : t s absement : A ms time : t s distance : d, position : r, s, x, displacement m area : A m angle : θ, angular displacement : θ rad solid angle : Ω rad, sr frequency : f s, Hz speed : v, velocity : v ms kinematic viscosity : ν, specific angular momentum : h m s frequency : f s, Hz angular speed : ω, angular velocity : ω rad s acceleration : a ms angular acceleration : α rad s jerk : j ms angular jerk : ζ rad s mass : m kg ML moment of inertia : I kg m MT momentum : p, impulse : J kg m s, N s action : S, actergy : א kg m s, J s ML T angular momentum : L, angular impulse : ΔL kg m s action : S, actergy : א kg m s, J s MT force : F, weight : F kg ms, N energy : E, work : W kg m s, J ML T torque : τ, moment : M kg m s, N m energy : E, work : W kg m s, J MT yank : Y kg ms, N s power : P kg m s, W ML T rotatum : P kg m s, N ms power : P kg m s, W Retrieved from `` https://en.wikipedia.org/w/index.php?title=Speed&oldid=802056066 '' Categories : Physical quantities Velocity Hidden categories : CS1 maint : Uses editors parameter Articles needing additional references from July 2016 All articles needing additional references Use British English from September 2015 Pages using deprecated image syntax Articles needing additional references from May 2013 Articles with too many examples Talk Contents About Wikipedia Wikiquote Afrikaans አማርኛ অসমীয়া Asturianu Azərbaycanca Brezhoneg Català ChiShona Cymraeg Dansk Eesti Español Esperanto فارسی Français Gaeilge Galego 한국어 हिन्दी Ido Bahasa Indonesia Interlingua IsiXhosa Íslenska ქართული Қазақша Kiswahili Kreyòl ayisyen Latina Lietuvių മലയാളം मराठी Bahasa Melayu Mìng - dĕ̤ng - ngṳ̄ नेपाली नेपाल भाषा 日本 語 Norsk Norsk nynorsk ਪੰਜਾਬੀ Polski Português Qaraqalpaqsha Română Русский Scots Simple English Soomaaliga کوردی Svenska Tagalog தமிழ் ไทย Türkçe Українська Tiếng Việt Võro Winaray 粵語 中文 Edit links This page was last edited on 23 September 2017, at 18 : 20. 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Question: knot is measure to known the speed of
Answer: nautical miles per hour