What is Kinetic energy: Definition and 1000 Discussions

In physics, the kinetic energy of an object is the energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest.
In classical mechanics, the kinetic energy of a non-rotating object of mass m traveling at a speed v is










1
2


m

v

2









{\displaystyle {\begin{smallmatrix}{\frac {1}{2}}mv^{2}\end{smallmatrix}}}
. In relativistic mechanics, this is a good approximation only when v is much less than the speed of light.
The standard unit of kinetic energy is the joule, while the English unit of kinetic energy is the foot-pound.

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  1. N

    Transfer of Kinetic Energy Through House Walls?

    Hello. I'm looking for a purely physical explanation for an unusual event that occurred in my home. The circumstances are humorous and creepy and cause for speculation concerning the paranormal. However, I believe we have identified the true cause of the phenomenon and want to vet it against...
  2. R

    Minimum Kinetic energy of the hydrogen atom

    Homework Statement A hydrogen atom collides with another hydrogen atom at rest. If the electrons in both atoms are in the ground state, what is the minimum kinetic energy of the hydrogen atom such that the hydrogen atom at rest will have its electron in the first excited state after collision...
  3. phasacs

    Why isn't Kinetic Energy always equal to Potential Energy?

    K= ∫mvdv = ∫m dx/dt dv = ∫m dx/dv dv/dt dv = ∫m dv/dt dx = ∫Fdx = U => K=U, why isn't this true? If it is, wouldn't that mean that Kinetic Energy is always equal to Potential Energy?
  4. H

    B Why does waveform exp[iwt] have negative kinetic energy?

    Why so? Quoted from Quantum Physics 3rd ed. by Stephen Gasiorowicz, p. 26. It was explaining why we ignore the terms with exp[iwt] when adding plane waves to form a wave packet:
  5. tranvannhancu

    Problem finding the total kinetic energy of bicycle system

    I've been working on this problem for a while and here comes the problem: I'm building a balancing system for a bicycle using Gyroscopic effect (take a look at Figure 2 for more details). My system consists of 2 parts: the bicycle itself a flywheel on top of it All parameters are given. The...
  6. N

    What % of PEg must be converted in KE in order to double v?

    Homework Statement What % of PEg must be converted in KE in order to double the speed of a pendulum? So I have spent a couple of days trying to figure out this problem (it's a lab), and I can't seem to figure it out. I have asked my physics teacher about it, and he said the answer to the...
  7. Y

    Help in Homework - Kinetic Energy

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  8. A

    Work, Gravitational Potential and Kinetic Energy, Spacecraft

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  9. G

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  10. boomdoom

    Kinetic energy density in a string (derivative)

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  11. L

    Relate rotational kinetic energy to potential energy

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  12. aatari

    Why does increasing mass also increase kinetic energy and velocity?

    Homework Statement Hi Guys, I don't have a particular problem that I need to solve but I need help with understanding a concept. So we agree that irrespective of mass of an object they will both fall at a same rate if there is no air resistance. However, why is it then when we increase the mass...
  13. R

    A Understanding Electron Kinetic Energy in Quantum Wells

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  14. H

    Collisions -- conceptual questions

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  15. P

    Kinetic energy in ocean current

    Homework Statement Consider an Ocean Current flowing at 2.5 m/s. a) How much energy is contained in a cubical block of water 1m on the side. (The density of the water is about 1030kg/m^3.) b) If the flow is perpendicular to one of the cube faced, what is the rate at which current flow carries...
  16. A

    What fraction of its energy does accelerating proton shed?

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  17. Jared

    Need help finding energy for escape velocity

    Homework Statement The gravitational potential energy of a certain rocket at the surface of the Earth is -1.9x10^12 J. The gravitational potential energy of the same rocket 300km above the Earth's surface is -1.8x10^12 J. Assume the mass of the rocket is constant for this problem. A) How much...
  18. Metovich

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  19. L

    Pascal's law and kinetic energy in pipes

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  20. P

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  21. StillLearningToronto

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  22. L

    What is the kinetic energy of a proton when neutron decays?

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  23. A

    What is the kinetic energy of particles in plasma

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  24. Z

    RMS speed in kinetic energy equation for gas

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  25. Shardul Khare

    What is the difference between Kinetic Energy and Speed?

    I know the formulae,but really don't understand the difference
  26. H

    Kinetic energy of plate tectonics problem

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  27. O

    B Rest Energy - Kinetic Energy

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  28. Z

    What is the Relationship Between Kinetic Energy and Momentum?

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  29. Low-Q

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  30. RavenBlackwolf

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  31. BitWiz

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  32. xjcov

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  33. J

    Kinetic Energy in Circular Motion: Is 1/2 m v^2 Still Applicable?

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  34. Cocoleia

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  35. J

    Understanding Work and Kinetic Energy: Examples and Calculations Explained

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  36. M

    Work done on brakes vs kinetic energy lost by vehicle

    When doing work on the brakes of a car or bicycle, how much of that energy is actually removed from the total kinetic energy of the vehicle? What is the most efficient braking system?
  37. I

    Does light contain kinetic energy?

    Does light contain kinetic energy as it moves, or does it require mass.
  38. V

    Should I consider Linear Kinetic Energy in this Equation

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  39. Konte

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  40. fuvest

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  41. A

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  42. I

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  43. C

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  44. Cocoleia

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  45. nickyfernandezzz

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  46. Ian Baughman

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  47. J

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  48. H

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  49. cheapstrike

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  50. Q

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