What is Kinetic: 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. M

    How Does Box Size Affect Kinetic Energy Calculations in Gas Molecules?

    In definition and proof of kinetic energy, it uses the second law of Newton. The length of the box is L and it uses this length to define the time of applying the force on the wall. Actually this time should be only time that molecule reaches to the wall and changes its velocity. My question...
  2. Nicodemus Rex

    Kinetic Vehicle [flywheel powered] mass and energy

    1200lb total vehicle weight 800lb total flywheel mass [4x200ea] Diameter 18.75" Flywheel RPM 3500 [120v electric motor plugged into wall] Pulley to drive wheel at 1:1 [6"pulley] or to 12' pulley Please help write the end of this story before I start. This is a "rev up" car built for...
  3. ZawL

    Getting energy from kinetic motion of air particles

    I am proposing a piece of equipment a bit similar to Crooke's radiometer with the aim of using kinetic motion of air particles to rotate the mill, without need for an external source of EM radiation. Instead of flat vanes as in Crooke's radiometer, I propose 3-dimensional vanes in the shape of...
  4. F

    Does Rotating a Gas Container Increase Its Temperature?

    If I place an insulated container of gas on the edge of a turntable and then rotate the container as a constant angular velocity, what happens to the gas? Does the temperature of the gas increase? If so, how was work done on the gas?
  5. B

    Kinetic energy and potential energy look very dissimilar

    The more I think about it the less clear the respective natures of kinetic energy and potential energy (and of their sum, the so-called total energy) become. The thing is I have the impression that once you try to go a bit further than the usual description of "scalar values assigned to systems...
  6. D

    I Kinetic and Potential energy operators commutation

    Hi All, Perhaps I am missing something. Schrodinger equation is HPsi=EPsi, where H is hamiltonian = sum of kinetic energy operator and potential energy operator. Kinetic energy operator does not commute with potential energy operator, then how come they share the same wave function Psi? The...
  7. Asmaa Mohammad

    The momentum and the kinetic energy

    Homework Statement Multiple choice question: The momentum of a body has increased by 25%, then its kenitic energy will roughly increase by... 1. 25% 2. 5% 3. 38% 4. 56% 5. 65% Homework Equations Pl = mv (Pl is the momentum, m is mass and v is velocity) K.E = 0.5 mv^2 The...
  8. R

    Mechanical energy to kinetic energy storage....?

    Can there be a system that utilizes mechanical energy to produce kinetic energy, but "storing" the mechanical energy to be used at a different time for kinetic energy? Like a bike where you pedal but don't move; that mechanical energy is waiting to be "released" by some mechanism *** exclude...
  9. 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...
  10. 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...
  11. 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?
  12. 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:
  13. 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...
  14. Y

    Help in Homework - Kinetic Energy

    Homework Statement Problem: http://imgur.com/a/Sw2zA Hi all, I was given this problem as homework and I have almost no clue on how to solve it. I have tried for some time with no luck. Homework Equations We learned about kinetic and potential energy as well as work. W = F*d W = delta KE PE =...
  15. A

    Work, Gravitational Potential and Kinetic Energy, Spacecraft

    Hi guys. I'm new to this forum so I'm not sure if I'm posting this in the right place or correctly, but I was totally stumped on a Physics 12 question as I was studying for my exam. The question is: An explorer spacecraft is descending towards Mars using a rocket engine for braking. The...
  16. herbertpbarreto

    Chemical Reaction Engineering homework

    Homework Statement The decomposition of phosphine 4PH3(g) + P4(g) + 6H2(g) is first-order with respect to phosphine with a rate constant k = 0.0155 s-l at 953 K. If the decomposition occurs in a constant-volume batch reactor at 953 K, calculate, for 40% conversion of PH3, (a) the time...
  17. E

    Find product kinetic energies in (α,γ) reaction

    Homework Statement 5.5 MeV alphas hit Be-9 and produce carbon with a gamma. the Q value is 10.65 I have to find the kinetic energy of the carbon nucleus and the gamma and I am to ignore the gamma ray momentum. Homework Equations T = p^2 / 2*m Q = T_be + T_alpha - T_c - T_gam[/B]The Attempt...
  18. T

    Work done by kinetic friction

    Homework Statement A 5.72 kg block is released from rest on an inclined surface. The incline makes an angle of 25.0 degrees relative to horizontal. The block is known to be traveling at a speed of 1.33 m/s after sliding a distance of 2.60 m along the incline. How much work was done on the block...
  19. boomdoom

    Kinetic energy density in a string (derivative)

    Homework Statement In our physics course, we were studying one dimensional waves in a string. There, our teacher stated that the kinetic energy in a small piece of a string is dK=\frac{1}{2}μdx\frac{\partial y}{\partial t}^2 were μ is the linear density of the string, so he claimed that...
  20. C

    When is the net torque=0?

    Homework Statement A child is initially sitting near the outer rim of a revolving merry-go-round. Suddenly, the child moves towards the center of the merry-go-round (while it is still revolving). For the merry-go-round+child system, let the symbols L and K refer to the magnitude of the angular...
  21. Z

    Kinetic Moments: Explaining their Role in Moment Equations

    Why are kinetic moments not included in the regular summation of the moments? In other words why is the equation ∑M = ∑Mk and not ∑M + ∑Mk = 0 ? I guess it would help if someone could explain exactly what a kinetic moment is, and why it is equal to the summation of the moments due to external...
  22. L

    Relate rotational kinetic energy to potential energy

    Homework Statement This problem is from the 2015 AP Physics C Mechanics free response, question 3 part b. https://secure-media.collegeboard.org/digitalServices/pdf/ap/ap15_frq_physics_c-m.pdf Homework Equations K = 1/2Iω2 U = mgh The Attempt at a Solution The potential energy of the bar when...
  23. Z

    Understanding Kinetic Moments: Why Do They Belong on Opposite Sides?

    Why don't we include the kinetic moments in the summation of the moments of a rigid body? In other words, why are the kinetic moments on the opposite side of the equation as the moments due to external forces? I understand that the math works out but it's not making sense to me conceptually...
  24. 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...
  25. Abhishek Gupte

    Find the kinetic coefficient of friction (mu)

    Homework Statement A 1.0x10^3 kg elevator carries a maximum load of 800kg Velocity = 3m/s Distance = .01km Net work = 13640J Homework Equations Force of friction = (m)(mu)(gravity) The Attempt at a Solution Gravity = friction 9.8 = (mu)(17640) .001 = mu
  26. R

    A Understanding Electron Kinetic Energy in Quantum Wells

    Hello to All ! I have a question that Whenever an electron from bulk material trapped by a quantum well that electron's 3rd dimensional kinetic energy component vanishes, But where that goes, is it added to the other 2 dimensional kinetic energy components..?
  27. H

    How to use the coefficient of kinetic friction?

    Homework Statement A child is playing with their Hot Wheel cars. They have set up a track which is initially horizontal but then ascends to a second horizontal section which is 50 cm higher than the initial track. The track is friction-less until the car reaches the upper section of the track...
  28. 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...
  29. L

    Pascal's law and kinetic energy in pipes

    If you have a U-shaped pipe like the attached image, with more fluid in the left column than the right, then the fluid will level out basically because of Pascal's Law. Force on the fluid is exerted on every part of it in equal direction etc.. So when the fluid levels itself it flows across to...
  30. StillLearningToronto

    How Much Kinetic Energy to Accelerate a Proton to 0.9999c?

    Question: Calculate the kinetic energy required to accelerate a single proton from rest position to 0.9999c. The mass of the proton is 1.67*10^-27 kg. Equations Used: Ek=(mc^2/√ 1-(v^2/c^2))-mc^2 Attempt at the problem: Ek=(1.67*10^-27kg)(3*10^8m/s)^2/√...
  31. L

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

    Homework Statement What is the kinetic energy given to the proton in the decay of a neutron when: a) The electron has negligibly small kinetic energy b) The neutrino has negligibly small kinetic energy Homework Equations Q = (mn - mp - me - mv ) c2 = .782MeV Where T is kinetic energy, and...
  32. A

    What is the kinetic energy of particles in plasma

    if i connect an electric current of 30 volts to argon gas to transform it to plasma, what is the average kinetic energy of the argon particles in that plasma?
  33. Z

    RMS speed in kinetic energy equation for gas

    I have been pondering. Why is it that we use the rms speed in the equation Ek = 1/2 m vrms2, as opposed to just the mean speed2
  34. Shardul Khare

    What is the difference between Kinetic Energy and Speed?

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

    Kinetic energy of plate tectonics problem

    Homework Statement One effect of plate tectonics is that the North American continental plate moves across the Earth’s surface at a speed of about 1.15 cm/yr. The North American plate has an area of about 35 million square kilometers, an average thickness of about 25 km, and a density of about...
  36. D

    Kinetic Theory - Mass on a piston

    Homework Statement A cylinder containing an ideal gas is in vertical position and has a piston of mass ##M## that is able to move up or down without friction (Fig. 13.2). If the temperature is increases, ...Fig (13.2) (a) both ##p## and ##V## of the gas will change. (b) only ##p## will...
  37. O

    B Rest Energy - Kinetic Energy

    We are giving a particle with mass 400 Mev/C2 and 200 MeV KE. What is the Energy of the particle? Is it 600 MeV or 200 MeV?
  38. Z

    What is the Relationship Between Kinetic Energy and Momentum?

    Homework Statement Homework Equations K.E = p^2/m The Attempt at a Solution [/B]
  39. Low-Q

    Force, mass, acceleration, kinetic energy

    Hi all, I stumbled into a somewhat odd mathematical problem, so I guess I've overlooked an important detail. If I have a mass of 1kg on wheels horizontally, and apply 10N of constant force so the mass is accellerating. I assume the velocity of that mass after 1 second is approx 10m/s. Then...
  40. S

    Calculating Forces and Kinetic Friction for a System of Connected Blocks

    Hi everyone, I'm having a difficult time figuring out this problem. Could someone give me some pointers? I set up the equations and the free body diagrams (hopefully they're correct) ; all I have to do now is solve for F.1. Homework Statement A block of mass m is on top of a block of mass M =...
  41. BitWiz

    Kinetic energy: Legal to use kinetically independent frames?

    A rocket is drifting in gravity-free space and is observed by an external observer who is also drifting at an unchanging location using an arbitrary coordinate system. The rocket accelerates at a fixed rate using a massless photon engine that results in a negligible change in the mass of the...
  42. Cocoleia

    DeBroglie wavelength based on kinetic energy

    Homework Statement I am working on a problem similar to this one: In this solution, I do not understand what mc is, can someone explain? Also, would I follow the same type of steps if I have the kinetic energy of a photon and I need it's wavelength? Homework EquationsThe Attempt at a Solution
  43. J

    Understanding Work and Kinetic Energy: Examples and Calculations Explained

    I am confused of how Work basically equals to Kinetic Energy...I will give an example just as way to help you help me get an idea about how it works...the example I thought of is... '' James (100 kg) jogs on a straight road at a constant velocity of 2.2 m/s for 600 seconds, how much energy does...
  44. 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?
  45. I

    Does light contain kinetic energy?

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

    Should I consider Linear Kinetic Energy in this Equation

    Sorry If the thread name confuse you. I want to know if I want to find the Torque from deriving Kinetic Energy and the system has Object the Rotate and the rotating cause linear motion(v). Let's say it a Rolling Disc on the non-slope plane which has angular velocity ω and that ω cause it to move...
  47. Konte

    I Internal rotation kinetic energy operator

    Hello everybody, My question today is: Given a molecule that has an internal degree of liberty ( let's take the ethane molecule with its internal rotation as an example), how to write the kinetic energy operator by means of the corresponding internal coordinate? Thank you guys. Konte
  48. A

    I How Do You Calculate the Average Orbital Kinetic Energy for Silicon?

    Hi! I search the way to calculate the average orbital kinetic energy like is given in :http://physics.nist.gov/cgi-bin/Ionization/bun.php?Id=AlI (here is for aluminum). I would like use the underlying method to calculate the average orbital kinetic energy for the silicon (Si) element. If you...
  49. Cocoleia

    Relativistic kinetic energy and momentum

    Homework Statement A proton has a speed of 0.2c. Find the speed of an electron that has (a) the same kinetic energy as the proton, and (b) the same momentum as the proton. Homework Equations K=ϒmc^2-mc^2 The Attempt at a Solution This is what I did for the same kinetic energy part, but I...
  50. S

    Calculate the Kinetic Frictional Force

    The alarm at a fire station rings and a 71.3-kg fireman, starting from rest, slides down a pole to the floor below (a distance of 3.63 m). Just before landing, his speed is 1.42 m/s. What is the magnitude of the kinetic frictional force exerted on the fireman as he slides down the pole? Givens...
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