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. chwala

    Find the car's speed at point when deceleration is increased - Mechanics

    Wawawawawawa! This was a tough one...:biggrin: Find the question below; Find my approach below: We have the following equations; 1. ##v=30-0.5t## 2. ##v=30-1.5t## Now the car changes its acceleration at some point i.e from ##-\frac{1}{2}## ##m/s^2## to ##-\frac{3}{2}## ##m/s^2## ... I...
  2. G

    I What is the speed of a shock wave?

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  3. chwala

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  4. fascinated

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  5. L

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    A, the train speed up?
  6. F

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    Why we know that average speed of a single photon(in point particle view) equal the speed of EM wave?If average speed of a single photon smaller than c then there exist massive photons?
  7. H

    A What is the achievable accuracy of neutrino speed measurement?

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  8. D

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  9. S

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  10. morrobay

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  11. sigurdfromnor

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  12. TylerSmith

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  13. Mr_Allod

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  14. L

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  15. brucegoth123

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  16. LCSphysicist

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  17. BadgerBadger92

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  18. S

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  19. Harli

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  20. M

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  21. rudransh verma

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  22. N

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  23. rudransh verma

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  24. DaveC426913

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  25. U

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  26. louis_slicka

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  27. brochesspro

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  28. R

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  29. mncyapntsi

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  30. I

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  31. K

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  32. L

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  33. M

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  34. P

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  35. J

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  36. S

    I Relative Speed of Light Between Objects

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  37. M

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  38. Huzaifa

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  39. F

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  40. Pratyeka

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  41. M

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  42. T

    Automotive Speed of a car rolling down a hill

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  43. L

    I Time Dilation: Variables Beyond Speed & Gravity?

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  44. nazmulhasanshipon

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    **My Attempt:** Here, I considered for 2 kg mass the resultant motion is zero, which means it's acceleration (a) would be zero. So, if we consider the Tension force from the 1.5 kg mass to keep 2 kg mass from falling is L, then 2×9.8-L=ma=2× 0 ⇒ L=19.6 N. But where does the tension force from...
  45. S

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    a. To find the speed, I need to find the height where the cords first become loose, which is when the cord is 25 m long. $$h=30-\sqrt{25^2 - 5^2}$$ But the teacher's working is ##h=30-\sqrt{25^2 - 4^2}## How to get 4? b. My idea is to use Newton's 2nd law so I draw free body diagram of the...
  46. S

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  47. H

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  48. David Lewis

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  49. chwala

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  50. Huzaifa

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