What is Speed: Definition and 1000 Discussions

In everyday use and in kinematics, the speed (commonly referred to as v) of an object is the magnitude of the rate of change of its position with time or the magnitude of the change of its position per unit of time; 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 (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph). 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.

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  1. B

    Speed of pendulum at certain angles

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  2. S

    Have a problem with this Rotational Motion question

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  3. P

    In jousting, how does speed affect the knight's lance?

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  4. T

    B Einstein's Epiphany of Constant Light Speed

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  5. Y

    Can the speed of sound in air be faster?

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  6. NoahCygnus

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  7. P

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  8. R

    B What limits the speed of a gravitational wave to c?

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  9. E

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  10. O

    Solve Coilgun Inefficiency & Measure Projectile Speed France

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  11. Sullivan Stockwell

    Speed of Light in Various Mediums

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  12. K

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  13. M

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  14. Pushoam

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  15. Scott_10438

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  16. O

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  17. Adam Rabe

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  18. Jamison Lahman

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  19. Ivan Bevanda E

    B Do gravity and acceleration alter the speed of light?

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  20. kkris1

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  21. Pushoam

    I Measuring Wave Speed: Reference Frame Considerations

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  22. R

    Asteroid close encounter: speed at perigee

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  23. Kaneki123

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  24. R

    B Why does light move at the speed it does

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  25. A

    Calculating distance from acceleration as function of speed

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  26. S

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  27. parshyaa

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  28. Nick Goodson

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  29. K

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  30. Sullivan Stockwell

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  31. S

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  32. Mike Dacre

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  33. baldbrain

    Speed of Sound using a Resonant tube

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  34. D

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  35. G

    Dynamics exam prep -- forces explanation in FBD please

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  36. R

    Time required for disk to reach angular speed?

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  37. nothing909

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  38. Superman123

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  39. R

    I In gravitational assistance, does the mass matter?

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  40. S

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  41. Deadawake

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  42. lightofthemoon

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  43. M

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  44. gelfand

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  45. gelfand

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  46. B

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  47. I

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  48. davidge

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  49. I

    Calculating Speed of Protons in a Linear Accelerator: 530 MeV Kinetic Energy

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  50. S

    I Speed of Light Logic: Flaw Explained

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