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. Eclair_de_XII

    Finding coefficient of kinetic friction from thermal energy?

    Homework Statement "A rope is used to pull a ##\frac{357}{100}kg## block at constant speed ##\frac{203}{50}m## across a horizontal floor. The force on the block from the rope is ##\frac{768}{100}N## and directed ##15°## above the horizontal. What are (a) the work done by the rope's force, (b)...
  2. D

    Derive the equation for kinetic energy and gravitional energ

    Homework Statement A wooden toy mouse of mass (m) is attached to a spring with constant (k) and suspended vertically as shown below. The toy is released at the point the spring is unstretched at position x = +A, passes through equilibrium at x = 0 and the spring’s maximum extension occurs at x...
  3. B

    To stop a moving object -- Momentum or Kinetic Energy

    How should I look at the problem at stopping a moving object with the following conditions 1) mass m and speed v 2) 0.5 m and 2v 3)0.5m and sqrt 2 v Simple math tells me the number 2 would require more energy to stop it. I can relate to energy better in terms of how to stop a moving mass...
  4. E

    What percentage of the original kinetic energy is convertible?

    Homework Statement Ball 1 has an inertia of 0.500 kg and ball 2 has an inertia of 0.600 kg . Ball 1 is moving away from you at 5.0 m/s, and you decide to throw ball 2 at it to make it go faster. The balls collide head-on, and the coefficient of restitution for the collision is 0.95. Part A)How...
  5. T

    I Substituting a solid body with mass points

    I ran into the following problem, and stuck for a couple of days now. I have a solid body, rigid and and has uniform density. Its mass M, the location of the center of gravity x_M, y_M, z_M and its inertia matrix is known: Jx Jxy Jxz Jyx Jyy Jyz Jzx Jzy Jz I have to write an algorithm...
  6. G

    Is Force a Conservative Vector Field?

    1. The problem statemees and given/known data A ball has a potential energy of 200J. Once the ball reached the ground, it's kinetic energy was 175J. Is this possible and does this defy the conservation of energy? Homework Equations KE = PE The Attempt at a Solution I am not sure. Being in high...
  7. J

    Change in Kinetic Energy/ Work

    Homework Statement Homework Equations ΔKE=W+FcosΘd KE=.5mv^2 Final Vel^2=initial Velocity^2+2ax The Attempt at a Solution So calculate the force at x=2.6 to -5.356N, set 2.6(-5.356)=1.3Vf^2-1.3(0^2) which seemed to prove a problem as the square of the final velocity was negative, but just...
  8. T

    Dashpots and the Work - Kinetic Energy Theorem

    Homework Statement I need to accommodate a dashpot in an intentionally simple work-kinetic energy analysis method. For example, for a box being dragged up a ramp via a rope while attached to a spring, I can deal with the work done by gravity, rope tension, spring force, and friction via the...
  9. terryds

    Static friction vs kinetic friction in Tablecloth trick

    In the tablecloth trick, if we pull the tablecloth with a great force, the objects on it will stay on the table. But, if we pull it gently, the objects on it will still get along with the cloth movement. I know that if the force exceeds the maximum value of static friction, the objects will...
  10. Green dwarf

    Is electromagnetic radiation a form of kinetic energy?

    Hi, I'm a high school science teacher. Most textbooks classify EM radiation as kinetic energy. But this doesn't seem right to me. As a photon is massless it's hard to see how it can have kinetic energy which is 1/2 mv^2. It could be said that it has energy hf and therefore mass hf/c^2. Then its...
  11. Mayan Fung

    I Exploring the Kinetic Energy Operator: Why is it Differentiated Twice?

    When I learned about operators, I learned <x> = ∫ Ψ* x Ψ dx, <p> = ∫ Ψ* (ħ/i ∂/∂x) Ψ dx. The book then told me the kinetic energy operator T = p2/2m = -ħ2/2m (∂2/∂x2) I am just think that why isn't it -ħ2/2m (∂/∂x)2 Put in other words, why isn't it the square of the derivative, but...
  12. A

    Kinetic Energy and Work/ Work depends on acceleration?

    1. Problem Statement: A worker lifts a heavy crate vertically 1.0 m in 2.0 s. If she lifts the same crate the same distance in 1.0 s, the work was done by her is A the same. B two times as great. C half as great. D four times as great. E one-fourth as great...
  13. energeticringleader

    Rest, Mass, and Kinetic Energy

    Homework Statement I really don't have a homework question just a thought. Is rest energy "maximum energy" for a particle? As to say a particle at rest has a given energy, so when it is in motion it transfers some mass energy to kinetic energy, where both the mass and kinetic energy together...
  14. F

    Video about pressure in kinetic theory

    Hi, I am looking for a video helping intuition on pressure, in the context of kinetic theory of gases. I remember seeing a video where someone poured a bucketful of little hard balls (lead sinkers for fishing?) onto an electronic scales (a dynamometer, really) showing that this corresponds to...
  15. Eclair_de_XII

    How to balance gravitational energy and kinetic energy?

    Homework Statement "In Fig. 8-33, a runaway truck with failed brakes is moving downgrade at ##130\frac{km}{h}## just before the driver steers the truck up a friction-less emergency escape ramp with an inclination of ##θ=15°##. The truck's mass is ##1.2⋅10^4kg##. What minimum length L must the...
  16. D

    I Storing Kinetic & Mechanical Energy

    How can kinetic or mechanical energy be stored?
  17. TheSodesa

    Maximum change in the kinetic energy of a particle

    Homework Statement Show that the largest possible change in the kinetic energy , ##\Delta E_{kin}##, of a particle of mass ##m## running into another particle of mass ##M## at rest in the lab coordinate system is \Delta E_{kin} = \frac{-4AE_{kin}}{(1+A)^{2}}, where ##A = \frac{M}{m}##...
  18. F

    Elements of plasma kinetic theory, Bittencourt

    Homework Statement Consider the motion of charged particles, in one dimension only, in the presence of an electric potential V ( x). Show, by direct substitution, that a function of the form f=f(1/mv^2 + qV) is a solution of the Boltzmann equation under steady-state conditions. Homework...
  19. R

    Absolute temperature for average translational kinetic energ

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  20. S

    How Does Velocity Relate to Kinetic Energy in Projectile Motion?

    Hey guys, this question has boggled my mind not because I don't know how to approach it but apparently the method I'm using is incorrect! Question A cannonball with a mass of 150 kg is fired from a cannon. The cannonball leaves the cannon with 447.9 kJ of kinetic energy. The cannon makes an...
  21. M

    Question on work energy and power kinetic energy of an ....

    Homework Statement If the speed of a vehicle increases by 2m/s then it's kinetic energy is doubled. Find out the original speed of the vehicle Homework Equations 1/2(mv^2) The Attempt at a Solution First find out both KE(kinetic energy) taking u(initial vel.) And v(final vel.) And mass as m...
  22. X

    Inelastic Collision: Kinetic Energy vs Momentum

    In an inelastic collision is the change in kinetic energy equal to the difference of final and initial momentum if one of the objects is initially at rest? For example: m1v = (m1+m2)Vf -----> 0 = (m1+m2)Vf - m1v1 1/2(m1+m2)Vf^2 - 1/2m1v^2 = (m1+m2)Vf - m1v1 Or totally wrong? Thanks!
  23. marsupial

    Coefficients of kinetic and static friction in a pulley

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  24. P

    Kinetic friction in an N,T- system only works in tangential?

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  25. F

    How to intuitively see the v^2 relation to kinetic energy?

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  26. S

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    A spring of spring constant k sits on a frictionless horizontal table, one end of the spring is attached to a wall the other end to a block of mass M= 2kg, also resting on the frictionless table. Another block of mass m=450g moving at a speed of 7m/s collides in-elastically with the block of...
  27. Gummy_Bear

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  28. JayaSuria

    Inelastic Collision - Kinetic Energy

    A 6.0kg metal ball moving at 4.0m/s hits a 6.0kg clay ball at rest and sticks to it. The two move at 2.0m/s. a. calculate the kinetic energy of the metal ball before it hits the clay ball. b. calculate the kinetic energy of the metal ball after it hits the clay ball. c. calculate the kinetic...
  29. Vavi Ask

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  30. S

    How Do You Calculate the Kinetic Energy of CO, CO2, and SO3 at 276 K?

    Homework Statement Calculate the kinetic energy of CO, CO2, and SO3 at 276 K . Homework Equations KE = (3/2) RT KE= (1/2)(mass)(velocity)^2 The Attempt at a Solution [/B] For CO: First attempt: KE=(3/2)(RT)=(3/2)(8.314 J/mol-K)(276K) = 3441.996 -- So that's wrong Second attempt: Relative...
  31. BlueQuark

    How can kinetic friction force be constant if....?

    As we all know, for the most part, the kinetic friction force is, for the most part, constant. After moving my cup across my table, this thought crossed my mind. If I move my cup across the table with a constant speed, then the force I'm applying must be equal to the kinetic friction force...
  32. J

    Calculate height and velocity given kinetic and potential?

    Homework Statement I have a table that needs to be filled out. In each column, potential and kinetic energy are given, but height and velocity are left blank. Ex: PE = 20 J, KE = 0 J, h = ?, V = ? Homework Equations KE = 1/2mv^2 U = mgh The Attempt at a Solution I'm totally stumped. How can I...
  33. D

    Final Frequency and Kinetic energy change?

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  34. R

    Kinetic Salt Effect - Size of Ions

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  35. bebop1

    Kinetic Energy and Collision Question

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  36. gennarakis

    I Quantum Kinetic Energy of Neutrons, Protons and Electrons

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  37. bebop1

    Kinetic Energy and Collision Question

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  38. C

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  39. D

    Angular Speed and Kinetic energy

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  40. B

    Kinetic Energy from a Simple Harmonic motion and spring

    Homework Statement A 0.26-kg block on a horizontal frictionless surface is attached to an ideal massless spring whose spring constant is 190 N/m. The block is pulled from its equilibrium position at x = 0.00 m to a displacement x = +0.080 m and is released from rest. The block then executes...
  41. Sugarteeth

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  42. T

    How does the distance between molecules affect temperature?

    Homework Statement According to the kinetic molecular theory: as the distance between the molecules increases, the temperature of a material decreasesthe rise in temperature of a material occurs because the molecules lose kinetic energywhen the molecules within a gas collide they lose energy...
  43. Nile Anderson

    Relationship between Velocity, Kinetic Energy and Mass

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  44. E

    Why is there a difference in kinetic energy among water molecules?

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  45. defaultusername

    What is the Correct Calculation for Sam's Speed at the Bottom of the Slope?

    Homework Statement Sam, whose mass is 75 kg, stands at the top of a 12-m-high, 100-m-long snow-covered slope. His skis have a coefficient of kinetic friction on snow of 0.07. If he uses his poles to get started, then glides down, what is his speed at the bottom? Homework Equations v =...
  46. Surya97

    How does anything slow down if kinetic friction is low?

    Lets say that there is a rectangular box on a horizontal surface, with no air resistance on it. If the applied force required to get the object moving is greater than the static friction, Fa>Us* Fn, then the object starts moving. However, the Static Friction is almost always greater than the...
  47. M

    Temperature & kinetic energy of particles in solid vs gas

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  48. K

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  49. T

    MHB Calculating Kinetic Energy of a Block on an Inclined Plane

    A block of mass 9kg is initially at rest at the top of an inclined plane of ramp length 4m. -Assuming that the plane is frictionless, calculate the speed of the block at the bottom of the plane. -Now instead assume the a frictionless force of Ffr = 2 Newtons opposes the motion of the block...
  50. E

    Chromatography: The difference in kinetic energy

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