Kinetic Definition and 1000 Threads

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.

View More On Wikipedia.org
Recent contents Top users
  1. alichoudhry57

    I Torque and Rotational Kinetic Energy Relationship

    I am wondering if it is possible to calculate either the Kinetic Energy or Rotational Kinetic Energy of an object if we have the Power (kW), Torque (Nm), and Speed (RPM) of the object.
  2. A

    Modal mass and kinetic energy in FEM modal analysis

    So, I use Ansys (well known FEM software) and get the next output for a modal analysis toy problem (If you happen to know Ansys that's a pre, but I promise it shouldn't matter). The problem is a simple beam, clamped at one end. I used 160 20-node brick elements to solve it (so no Timoshenko...
  3. Ahmed1029

    I Time dependence of kinetic energy in Lagrangian formulation

    Could kinetic energy possibly depend explicitly on time in the lagrangian for some arbitrary set of generalized coordinates?
  4. Rikudo

    Kinetic energy of a composite body

    This is my answer: $$KE_{total}=KE_{centermass}+KE_{uppermass}+KE_{bottommass}$$ $$KE_{total} = \frac 1 2 (mv^2 + 2m(\vec {v} + \vec {wL})^2) $$ But, the solution manual says that the answer is this: $$KE_{total} = \frac 1 2 (mv^2 + 2m(v^2+w^2L^2)) $$ I think he regard this composite body as...
  5. zaki belh

    A Question about kinetic theory and hydrodynamics (in plasmas)

    It is usual, in plasma physics, to combine the kinetic description for electron fluid and the hydrodynamic description for ion fluid, when studying the plasma properties or the dynamics of the electrostatic waves. I am wondering what are the physical meaning and limits of such an approach. Thanks.
  6. SkyeAlen

    Kinetic Energy of a Charged Particle near a Charged Ring

    A point charge of value q=8uC is released from rest at a point 1.5m away from the center of the axis of a ring with uniform charge density 3uC/m. The ring has a radius of 10 cm. What is the kinetic energy of this charge when it is 4.5 cm from the center of the charge ring, considering that it is...
  7. E

    Potential and Kinetic energy equations including drag coefficient

    1. Golf ball initial potential energy uncertainty (110-5kg 0.01 m 0.01m/s2)= 110-9J4.31210-5=4.31210-14j 2. Golf ball initial potential energy calculation (4.4 x10-4kg 9.8 m/s2 0.609 m)= 4.31210-54.31210-14j 3.Golf ball final potential energy uncertainty ( 110-5kg 0.0 m0.01 m/s2)= 0.0 J 4...
  8. Green dwarf

    I Exploring Energy in Astronomy: Kinetic, Potential & Mass?

    I am planning to teach a school astronomy group about energy. Most people seem to accept that there are two types: kinetic energy, resulting from movement; potential energy, resulting from position in a force field with a potential gradient (convertible to KE if the object is allowed to move...
  9. D

    Can High Velocity Cause Hailstones to Melt?

    I'm pretty sure the hailstones are likely to melt/disperse because 824 m/s is a high velocity but can someone help me elaborate why it would melt?
  10. R

    I Why is momentum considered a vector and kinetic energy a scalar?

    I'm not interested in the mathematical derivation, the mathematical derivation already is based on the assumption that momentum is a vector and kinetic energy is a scalar, thus it proves nothing. Specifically, what happens if we discuss scalarized momentum? What happens if we discuss vectorized...
  11. P

    Lagrangian of a double pendulum, finding kinetic energy

    This is from Taylor's classical mechanichs, 11.4, example of finding the Lagrangian of the double pendulum Relevant figure attached below Angle between the two velocities of second mass is $$\phi_2-\phi_1$$ Potential energy $$U_1=m_1gL_1$$ $$U_2=m_2g[L_1\cos(1-\phi_1)+L_2(1-\phi_2)]$$...
  12. Dario56

    I Kinetic Energy and Potential Energy of Electrons

    Time indepedendent Schrödinger equation for a system (atom or molecule) consisting of N electrons can be written as (with applying Born - Oppenheimer approximation): $$ [(\sum_{i=1}^N - \frac {h^2} {2m} \nabla _i ^2) + \sum_{i=1}^N V(r_i) + \sum_{i < j}^N U(r_i,r_j)] \Psi = E \Psi $$ Terms in...
  13. A

    Finding kinetic energy and initial velocity of a cart over time

    Here's my list of variables and things to account for: m=100kg Wnc=5000J Wfriction=-500J -Kinetic energy will be doubled (though I don't know how that plays into it exactly) -I don't think there's any PE because it's on level ground My idea of what the equation might be: Wnc +1/2mv^2initial =...
  14. rudransh verma

    B About verification on Kinetic energy and work

    1. From resnik, Halliday “Kinetic energy K is energy associated with the state of motion of an object. The faster the object moves , the greater is the kinetic energy” If I am right this means that greater the kinetic energy, greater is its speed. 2. Force transfers energy to the body due to...
  15. L

    Work and kinetic energy comprehension question

    Hello, I’ll start by saying I have the answers and the steps to the solutions, but there’s a comprehension disconnect somewhere that I’m trying to figure out. There are two parts to my question but the second one may not apply depending on the answer to the first. I wasn’t sure from the forum...
  16. L

    I The time derivative of kinetic energy

    Lets consider T(\vec{p})=\frac{\vec{p}^2}{2m}=\frac{\vec{p}\cdot \vec{p}}{2m}. Then \frac{dT}{dt}=\vec{v}\cdot \vec{F}. And if we consider T=\frac{p^2}{2m} than \frac{dT}{dt}=\frac{1}{2m}2p\frac{dp}{dt} Could I see from that somehow that this is \vec{v}\cdot \vec{F}?
  17. R

    I Kinetic Energy derivation assumption?

    The classical definition to the Kinetic Energy equation is KE=integral of F*dx where F=d(m*v)/dt. When mass is constant, KE=(1/2)m*v^2. I am working on a vibration problem at work and having to review my Lagrangian Dynamics books from 30 years ago. So my question is about all of the authors...
  18. V

    Kinetic & Potential Energy of a Pendulum

    When the pendulum is released, the Kinetic Energy should be 0. When the pendulum is at the bottom/hits the rod, it should have 0 potential energy. However, I don't quite understand what happens after it hits the rod.
  19. J

    Equation calculations about the coefficient of kinetic friction

    I need an expert to verify equations about the coefficient of kinetic friction.
  20. C

    B Colliding balls: Conservation of momentum and changes in kinetic energy?

    I got curious about firearm ballistics and googled something similar to "bullet momentum vs kinetic energy". IIRC, momentum P = mv (checked); and kE = (mv^2)/2 (also checked). So I essentially wondered if it's worse to get hit by a bullet with greater kE than by one with lesser kE, presuming...
  21. Iwanttolearnphysics

    About Kinetic Energy of a ball falling vertically and bouncing up

    Hello again. I don't believe there are rules about posting twice in a day. I'm not a student and I answer Physics questions as a hobby, but I've only just started learning, so please help me out. I'm answering IBDP Physics questions. Here's my thinking: KE is not a vector quantity, so it's...
  22. M

    Find Final Kinetic Energy of a particle subject to two forces

    I'm having trouble putting the rest of the equations together, I believe I need the different from (0,0,0) to (1,0,0) and then (1,0,0) to (1,1,0) right? Then solve for x direction and y direction. What would I use for Wnc tho? I'm very confused.
  23. san12345

    Spring potential and kinetic energy

    please help me
  24. DonutHole

    Coefficient of kinetic friction

    Fn = 53 X 9.81 X cos 22 Fnet = 524 – 53 X 9.81 sin 22 + μ X 53 X 9.81 cos 22
  25. G

    I Is GHG Theory/GW in conflict with Kinetic Theory of Gases?

    Hi, Folks,...new around here. Please excuse my naivete, but-- I have a problem with the physics behind GHG Theory/GW. Most discussions seem to center around absorbtion/transmission spectra of gases, their correlation with temperature, ala' Black Box radiation and such, and the fact that GHG...
  26. K

    I Kinetic energy depends on ##\theta## but this argument says otherwise

    A free particle with coordinates as shown has kinetic energy ##T = \frac{1}{2}m\left(\dot r^2 + r^2\dot\theta^2 + r^2\sin^2\theta\dot\phi^2\right)## So we see ##T## depends on ##\theta##. Now suppose we rotate our coordinate system such that only one coordinate ##\theta## changes from...
  27. Tertius

    I Is Entropy the inexorable conversion of potential to kinetic energy?

    I know the math behind these, and I'm happy to use more precise language if needed, I just wanted to get some input on this sweeping generalization that entropy is the conversion of potential to kinetic energy. A brief summary of two important branches of entropy: 1) thermodynamics - the total...
  28. MattGeo

    I Reference Frame, Difference in Kinetic Energy, Fuel Consumed

    Say 2 cars are traveling side by side at 10 m/s in some flat, wide open space. Relative to each other they are stationary. Relative to someone on the ground they are both moving at 10 m/s. Now say you're in 1 of the cars and you see the other car accelerate, changing his velocity by 10 m/s in...
  29. I

    I Kinetic vs Gravitational Time Dilation: Perceived Speed

    As an object approaches a black hole’s event horizon, it experiences increasing gravitational time dilation, causing it to appear to an outside observer to slow down, until, at the event horizon, it appears to stop. An object traveling in space that increases its velocity from one...
  30. T

    Applications Involving Drying -- Using Kinetic Models

    Hi, I am a mechanical student. I would like to ask are those drying kinetic equations for food drying applicable in drying a paperboard? Thankyou :)
  31. F

    Kinetic and potential energy of a particle attracted by charged sphere

    Hello, I have a particle at point A with charge ##q_A##, and an unmovable sphere of radius ##R_B## at point B with a volumic charge density ##\rho##. The distance from particle A to the centre of the sphere in B is ##r##. Both objects have opposed charges, so, the particle in A, initially at...
  32. S

    MHB Calculating Kinetic Energy After Collision of Balls A & B

    Ball A of mass 2kg, is moving in a straight line at 5 m/s. Ball B of mass 4kg is moving in the same straight line at 2 m/s. Ball B is traveling directly towards Ball A. The balls hit each other and after the impact each ball has reversed its direction of travel. The kinetic energy lost in the...
  33. S

    How does gravity convert potential energy to kinetic?

    If I hold a ball above the ground, it has potential energy. Once gravity pulls on it, it becomes kinetic. What is gravity and how does it convert one kind of energy to another?
  34. greg_rack

    B How to relate relativistic kinetic energy and momentum

    Hi guys, a special relativity problem requested to choose the right graph representing relativistic momentum ##p## as a function of rel. kinetic energy ##K##, from these four: At first, I tried writing ##p## as a function of ##K##, in order to then analyze the function's graph and see if it...
  35. akashpandey

    Why do we add Kinetic and Potential energy?

    As we know Energy is a scalar quantity. So when we add kinetic and potential energy to get Total energy. So addicting these two energy (kinetic and potential) comes under Scalar addition ? I just wanted to confirm it.
  36. P

    Equations of motion of damped oscillations due to kinetic friction

    Take rightwards as positive. There are 2 equations of motion, depending on whether ##\frac {dx} {dt} ## is positive or not. The 2 equations are: ##m\ddot x = -kx \pm \mu mg## My questions about this system: Is this SHM? Possible method to solve for equation of motion: - Solve the 2nd ODE...
  37. V

    Deriving a formula for Kinetic Energy

    I have no idea how to do this. I've tried conservation of mechanical energy and it didn't work. Ek = Kinetic Energy R = horizontal range of the ball h = height from which the ball is released
  38. P

    Thermodynamics problem (ideal gas law, kinetic theory, processes, etc.)

    It is a long problem, but it is simple to understand. I am having trouble with part A. My attempt: Pressure outside > pressure inside container. pV = constant (isothermal). At equilibrium, all gases are at atmospheric pressure. Because it is quasi-static, the pressures of both compartments are...
  39. H

    Confirming Conservation of Kinetic Energy: An Explanation

    D is correct, the reasoning is as follows: 1/2*(M1V1)^2 + 1/2*(M2V2)^2 = 1/2 * (M1 + M2) (Vcm)^2, since V1 =V2 =Vcm KE retained = KE final = 1/2 *M(Vcm)^2 Let me know if reasoning is okay? However, why A isn't correct?
  40. Domuks

    How do I find average kinetic energy if I don't have mass of the gas?

    So always in my problems i had mass (M) but now i don't and it seems impossible to solve this problem if I don't have mass I think i am missing something. I was looking for similar problems in my book and internet and didn't find any.
  41. J

    Kinetic energies in two reference frames

    A very basic and simple query, but I can't see my way through it. A mass m moves at speed v1 relative to a truck traveling at speed v2 , fig.a. All components except this mass are massless. In a truck-stationary frame, the mass collides with a barrier on the truck liberating kinetic...
  42. J

    Doubt regarding functional derivative for the Thomas Fermi kinetic energy

    I have some doubts with respect on how the functional derivative for the kinetic energy in density functional theory is obtained. I have been looking at this article in wikipedia: https://en.wikipedia.org/wiki/Functional_derivative In particular, I'm interested in how to get the...
  43. AN630078

    Can heat flow into a body without increasing the mean kinetic energy?

    Yes, heat can flow into a body without increasing the mean kinetic energy of its molecules. Transferring heat energy to an object will raise its internal energy, this will not necessarily cause an increase in temperture. Specific latent heat is the energy required to change the state of one...
  44. TonyCross

    Friction/heat kinetic energy - reactive force

    Hi, Could anyone please give me a little advice. If we look at a disc brake on a vehicle, the disc brake pads apply a friction force on the disk rotor which causes the kinetic energy of the moving vehicle to be turned into heat. Does this heat reduce the reactive force experienced on the disks...
  45. guyvsdcsniper

    Does coefficient of kinetic friction depend on speed?

    In this part of the lab we pushed a block on a flat table and let it slide until it stopped. So it is decelerating with no force being applied to it while moving. In this case acceleration is negative. The only force acting on it is kinetic friction. Therefore I have come up with the following...
  46. Krokodrile

    Calculating Kinetic & Potential Energy: Is it Correct?

    In this problem i don't find any way to obtain de kinetic energy in KJ/Kg because when i resolve the kinetic energy formula the result its: 1/2 (1300 kg/s) (9 m/s)^2 = 5850 kg * m/s (i don't obtain m^2/s^2, so KJ/Kg its not possible) In the potential energy (w) part i obtain this: m*g ( i don't...
  47. H

    Comparing the kinetic energies among a solid sphere, a cylinder and a hoop

    I did the question as attached, so I think A and D are correct but the given answer is E. Where am I wrong? Thanks.
  48. HoneyBee

    Chemistry Finding rate constant from pressure change in an experiment

    Is there any way that I can find concentrations and then find the rate constant, k? And, using them, make an Arrhenius graph to find activation energy (including the catalyst)? Any help would be much appreciated. Change in pressure was found using a Vernier Gas Pressure Sensor. The starting...
  49. docnet

    Expectation value of kinetic energy operator

    The expectation value of the kinetic energy operator in the ground state ##\psi_0## is given by $$<\psi_0|\frac{\hat{p^2}}{2m}|\psi_0>$$ $$=<\psi_0|\frac{1}{2m}\Big(-i\sqrt{\frac{\hbar mw}{2}}(\hat{a}-\hat{a^{\dagger}})\Big)^2|\psi_0>$$ $$=\frac{-\hbar...
  50. H

    Question about the Kinetic Energy of a baseball in flight

    A baseball is thrown and lands 120 m away. While the ball is in flight, assuming the effect of air friction is negligible, which of the following is true? a. At maximum height the ball has its greatest kinetic energy. b. The horizontal component of the baseball’s kinetic energy is constant. c...
Back
Top