# speed

Speed - Wikipedia Speed From Wikipedia, the free encyclopedia Jump to navigation Jump to search Magnitude of velocity 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.Find sources: "Speed" – news · newspapers · books · scholar · JSTOR (July 2016) (Learn how and when to remove this template message) SpeedSpeed 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 symbolsvSI unitm/s, m s−1DimensionL T−1In 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 = 299792458 metres per second (approximately 1079000000 km/h or 671000000 mph). Matter cannot 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 Difference between speed and velocity 1.5 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, that is v=dt,{\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˙|=|drdt|.{\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=dsdt.{\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. Average speed of an object is Vav = s÷t Difference between speed and velocity Speed denotes only how fast an object is moving, whereas velocity describes both how fast and in which direction the object is moving. If a car is said to travel at 60 km/h, its speed has been specified. However, if the car is said to move at 60 km/h to the north, its velocity has now been specified. The big difference can be discerned when considering movement around a circle. When something moves in a circular path and returns to its starting point, its average velocity is zero, but its average speed is found by dividing the circumference of the circle by the time taken to move around the circle. This is because the average velocity is calculated by considering only the displacement between the starting and end points, whereas the average speed considers only the total distance traveled. Tangential speed Part of a series of articles aboutClassical mechanicsF→=ma→{\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 Inertial 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 mechanicsHamiltonian mechanicsRouthian mechanicsHamilton–Jacobi equationAppell's equation of motionUdwadia–Kalaba equationKoopman–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 Huygens Newton Kepler Horrocks Halley Euler d'Alembert Clairaut Lagrange Laplace Hamilton Poisson Daniel Bernoulli Johann Bernoulli Cauchy vteLinear 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∝rω,{\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=rω.{\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−1 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 = 299792458 m/s).Conversions between common units of speed m/s km/h mph knot ft/s 1 m/s = 1 3.6 2.236936 1.943844 3.280840 1 km/h = 0.277778 1 0.621371 0.539957 0.911344 1 mph = 0.44704 1.609344 1 0.868976 1.466667 1 knot = 0.514444 1.852 1.150779 1 1.687810 1 ft/s = 0.3048 1.09728 0.681818 0.592484 1 (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.Find sources: "Speed" – news · newspapers · books · scholar · JSTOR (May 2013) (Learn how and when to remove this template message)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 0.00000001 0.00000003 0.00000004 0.00000002 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 durationSprint 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 bicycleMuzzle 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 35000 ft (10668 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 1125 1235 768 Mach 1 by definition. 20 °C = 293.15 kelvins. Muzzle velocity of a 7.62×39mm cartridge 710 2330 2600 1600 The 7.62×39mm round is a rifle cartridge of Soviet origin Official flight airspeed record for jet engined aircraft 980 3215 3530 2194 Lockheed SR-71 Blackbird Space shuttle on re-entry 7800 25600 28000 17,500 Escape velocity on Earth 11200 36700 40000 25000 11.2 km·s−1Voyager 1 relative velocity to the Sun in 2013 17000 55800 61200 38000 Fastest heliocentric recession speed of any humanmade object. (11 mi/s) Average orbital speed of planet Earth around the Sun 29783 97713 107218 66623 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) 299792458 983571056 1079252848 670616629 Exactly 299792458 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: SpeedRichard 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. ^ 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. ^ a b c Elert, Glenn. "Speed & Velocity". The Physics Hypertextbook. Retrieved 8 June 2017. ^ a b c Hewitt (2006), p. 42 ^ "IEC 60050 - Details for IEV number 113-01-33: "speed"". Electropedia: The World's Online Electrotechnical Vocabulary. Retrieved 2017-06-08. ^ 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. ^ a b Hewitt (2006), p. 131 ^ Hewitt (2006), p. 132 ^ http://www.kickspeed.com.au/Improve-measure-kicking-speed.html ^ "Archived copy". Archived from the original on 2013-08-11. Retrieved 2013-10-12.CS1 maint: Archived copy as title (link) ^ Darling, David. "Fastest Spacecraft". Retrieved August 19, 2013. ^ 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 ^ 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. ^ 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) vteKinematics ← Integrate … Differentiate → Absement Displacement (Distance) Velocity (Speed) Acceleration Jerk Jounce Crackle Pop vteClassical mechanics SI unitsLinear/translational quantities Angular/rotational quantities Dimensions 1 L L2 Dimensions 1 1 1 T time: ts absement: Am s T time: ts 1 distance: d, position: r, s, x, displacementm area: Am2 1 angle: θ, angular displacement: θrad solid angle: Ωrad2, sr T−1 frequency: fs−1, Hz speed: v, velocity: vm s−1 kinematic viscosity: ν,specific angular momentum: hm2 s−1 T−1 frequency: fs−1, Hz angular speed: ω, angular velocity: ωrad s−1 T−2 acceleration: am s−2 T−2 angular acceleration: αrad s−2 T−3 jerk: jm s−3 T−3 angular jerk: ζrad s−3 M mass: mkg ML2 moment of inertia: Ikg m2 MT−1 momentum: p, impulse: Jkg m s−1, N s action: 𝒮, actergy: ℵkg m2 s−1, J s ML2T−1 angular momentum: L, angular impulse: ΔLkg m2 s−1 action: 𝒮, actergy: ℵkg m2 s−1, J s MT−2 force: F, weight: Fgkg m s−2, N energy: E, work: W, Lagrangian: Lkg m2 s−2, J ML2T−2 torque: τ, moment: Mkg m2 s−2, N m energy: E, work: W, Lagrangian: Lkg m2 s−2, J MT−3 yank: Ykg m s−3, N s−1 power: Pkg m2 s−3, W ML2T−3 rotatum: Pkg m2 s−3, N m s−1 power: Pkg m2 s−3, W Retrieved from "https://en.wikipedia.org/w/index.php?title=Speed&oldid=912393656" Categories: Physical quantitiesVelocityHidden categories: CS1 maint: Archived copy as titleCS1 maint: Uses editors parameterArticles with short descriptionArticles needing additional references from July 2016All articles needing additional referencesUse British English from September 2015Articles needing additional references from May 2013Articles with too many examples from May 2014All articles with too many examplesWikipedia articles with style issues from May 2014 Navigation menu Personal tools Not logged inTalkContributionsCreate accountLog in Namespaces ArticleTalk Variants Views ReadEditView history More Search Navigation Main pageContentsFeatured contentCurrent eventsRandom articleDonate to WikipediaWikipedia store Interaction HelpAbout WikipediaCommunity portalRecent changesContact page Tools What links hereRelated changesUpload fileSpecial pagesPermanent linkPage informationWikidata itemCite this page In other projects Wikiquote Print/export Create a bookDownload as PDFPrintable version Languages Afrikaansአማርኛالعربيةঅসমীয়াAsturianuAzərbaycancaবাংলাBân-lâm-gúBrezhonegCatalàChiShonaCymraegDanskEestiEspañolEsperantoفارسیFrançaisGaeilgeGalego한국어हिन्दीIdoBahasa IndonesiaInterlinguaIsiXhosaÍslenskaKabɩyɛქართულიҚазақшаKiswahiliKreyòl ayisyenLatinaLatviešuLietuviųമലയാളംमराठीBahasa MelayuMìng-dĕ̤ng-ngṳ̄Монголनेपालीनेपाल भाषा日本語NorskNorsk nynorskਪੰਜਾਬੀPolskiPortuguêsQaraqalpaqshaRomânăРусскийSarduScotsSicilianuසිංහලSimple EnglishSoomaaligaکوردیСрпски / srpskiBasa SundaSvenskaTagalogதமிழ்ไทยTürkçeУкраїнськаTiếng ViệtVõroWinaray吴语粵語中文 Edit links This page was last edited on 25 August 2019, at 08:10 (UTC). 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