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. navneet9431

    Motion when Kinetic Friction is more than Static Friction

    Homework Statement How would the motion of the block look like when the Force of kinetic friciton is more than the Limiting value of static friction? Homework Equations Kinteic Friciton=μN The Attempt at a Solution I think the block after overcoming the limiting value of static friction will...
  2. CRuff

    Calculating kinetic energy turned into Pressure (Pascals) during an impact

    Hello, A silly question I'm sure, if a projectile moving at 13.59 m/s with a KE = 527.47 J hits an area of 3 cm^2, what is the force transfer to that area and the resultant pressure applied expressed in Pascals? Do I divide the KE by a volume instead of area to Pa?
  3. K

    4-derivative kinetic term Lagrangian

    Homework Statement Show that $$L=\phi\Box^2\phi$$ generates negative energy density. Homework EquationsThe Attempt at a Solution The energy density is $$E=\frac{\partial L}{\partial \dot{\phi}}\dot{\phi}-L$$ Also the Lagrangian can be rewritten (using divergence theorem) as...
  4. S

    Kinetic friction direction on two stacked blocks

    If i have two blocks on top of each other and there is friction between the two blocks and it's a kinetic friction ( given μk). if i was given the force applied on the lower block to the right direction for example. ignoring the friction between the lower block and the ground, i tried to draw...
  5. jamiebean

    The formulae for kinetic energy and Joules

    The formula for kinetic energy is 0.5x kg x v^2, where v= velocity The formula for joules is kg x v^2 I don't understand why does the difference exist and what is the difference between joules and kinetic energy isnt joule the unit for energy?? Thank you guys for helping me.
  6. D

    Kinetic energy loss in disintegrated matter

    What happens to the kinetic energy when an object is disintegrated? Does it survive? For example, if I throw a baseball at the sun at 100 mph, I will get X amounts of heat energy released and X amount of light as it burned up before contact. If I threw another baseball 100,000 mph into the sun...
  7. K

    Calculating the Maximum Kinetic Energy of pions

    Homework Statement The problem is to Use the rest energy values in table 1 to calculate the maximum kinetic energy of the pions assuming the kaon is at rest before it decays. Rest Energies of pions are π- 140, π0 135 and π+ 140. Rest energies of kaons K- 494, K0 498 K+ 494 Homework...
  8. F

    Distance traveled with linearly increasing kinetic energy

    Homework Statement An object of mass 50 kg gains 20,000,000 joules every second. Devise formulae to find the distance covered at any given point in time, and the time necessary to cover a certain distance. Homework EquationsThe Attempt at a Solution E = 20,000,000 * t V = (E * 2/50)1/2 That's...
  9. W

    B Relativistic Kinetic Energy: Does Mass Change?

    Hello, According to Special Relativity, the mass of an object must increase as its speed approaches the speed of light. m=m0γ In the formula that allows us to calculate the kinetic energy of a body, KE=0.5mv2, should we take into consideration such increase in mass? Weam Abou Hamdan Wednesday...
  10. Krushnaraj Pandya

    Kinetic energy of a photoelectron

    Homework Statement Why is the value hf-w equal to maximum kinetic energy (not just kinetic energy) for a photoelectron? 2. The attempt at a solution w is the energy needed for electron to escape the surface, so the rest should convert to KE, and no such need for defining KE(max) should be...
  11. Ennio

    Formulating the kinetic energy of an object - helical motion

    Hi guys, I need your support to formulate the kinetic energy of an object: - having mass m [Kg] - rotating with angular velocity o [rad/sec] referred to an axis t [m] distant (and parallel) to the symmetry axis of the object - moving along the direction of its symmetry axis with a costant...
  12. JessiLim

    Static and Kinetic Friction vs Normal Reaction Graphing

    How do i suppose to determine the uncertainty for the slope of my Static friction against normal reaction graph? My data for static friction and normal force has the uncertainty of +/- 0.0001 The uncertainty is too small for me to draw airbox/bar in the graph to draw the max and min slope...
  13. T

    B Is the kinetic energy of a particle quantized?

    Is the kinetic energy of a particle quantized? Does it increase and decrease in discreet amounts?
  14. Monsterboy

    Kinetic energy and momentum in an elastic collision

    Homework Statement Mass m1 = 2kg traveling at v = 3 m/s Mass m2 = 3kg traveling at v = 2 m/s After an elastic collision (from opposite directions) what will be the momentum and velocities of each of the bodies ? Homework Equations [/B] Momentum = mass x velocity ##K.E = \frac {1}{2}.m.v^2 ##...
  15. S

    I Particle acceleration and kinetic energy

    Hi, I was reading about magnetic reconnection in astrophysical plasma and it says that magnetic reconnection transforms magnetic energy into heat via ohmic dissipation, particle acceleration and kinetic energy. It is not clear to me the difference between particle acceleration and kinetic...
  16. GabrielLight

    I About gravitational binding energy and kinetic energy

    If a celestial body's kinetic energy (say, the Moon's) surpassed the energy necessary to exceed the gravitational binding energy (GBE), would said body break apart because of it? For example, the Moon is currently orbiting the Earth at a speed of 1020 meters per second, giving it a kinetic...
  17. C

    I Total or kinetic energy in Bethe Bloch stopping power?

    The average loss of energy in a material per unit length of a particle (in particular an electron, which is stable) is described by the quantity ##dE/dx##. - for ionization it is given by the Bethe-Bloch formula $$-\left\langle {\frac {dE}{dx}}\right\rangle ={\frac {4\pi }{m_{e}c^{2}}}\cdot...
  18. S

    Kinetic term in the Hamiltonian

    Homework Statement Consider a point mass m attached to a string of slowly increasing length ##l(t)##. Them motion is confined to a plane. Find L and H. Is H conserved? Is H equal to the total energy? Is the total energy conserved? Assume ##|\dot{l}/l|<<\omega## Homework EquationsThe Attempt at...
  19. A

    Do electromagnetic waves have potential and kinetic energy

    Do electromagnetic waves have potential and kinetic energy like springs, strings, etc. If so how are they calculated, inter-related? What is the total energy? Are the energies fluctuating over time? I am a physics hobbyist so generally the first answers should come with the least mathematics...
  20. M

    Kinetic Energy vs Flow Work: Exploring the Difference

    As per work energy principle, the energy spent in moving an object is stored as kinetic energy.Flow work is done to make the fluid move.Why is it not included in kinetic energy (i.e) why kinetic energy and flow work are considered seperately?
  21. Ushitha Dissanayake

    How to find the coefficient of kinetic friction

    Homework Statement The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is: A) 0.062 B) 0.25 C) 0.41 D) 0.62 E) 1.2 Homework Equations I'm not too sure but i know that : If the...
  22. C

    Maximum kinetic energy / cutoff potential problem

    Homework Statement Light with a wavelength of 630nm is directed at a metallic surface that has a work function of 1.5 eV. Find:a) The maximum kinetic energy of the emitted electrons. b) The cutoff potential required to stop the photoelectrons. Homework Equations Ek = hc / λ - W Ek = eVo...
  23. vysqn

    Ek vs engine power in cars and space

    Help me please:) (1) An idealized engine with constant torque curve means constant acceleration. So for example if there is no air resistance and no frictions and car is on fixed gear and at 3000Rpm it produces 50Hp so at 6000Rpm will produce 100Hp. So he doubles the speed , doubles power and...
  24. A

    Kinetic energy of a bouncing ball

    Homework Statement I'm trying to find the coefficient of restitution (COR) and energy loss upon impact of a bouncing ball, and I'm trying to understand how these relate to each other. Homework Equations COR=sqrt(2gh/2gH) suvat equations (possibly) 1/2mv^2=mgH (using m=0.0585kg, g=9.8) energy...
  25. Clara Chung

    How do I calculate the work done in a kinetic theory problem?

    Homework Statement Homework EquationsThe Attempt at a Solution How to do part biii? I tried to find change of U and W, then use ΔU-W=Q=0. I can find the change in U by using the fact the rms of the x-component of the velocity is doubled. Therefore, originally, if isotropic <c2> =...
  26. Lukeblackhill

    Reduce Kinetic Energy Losses when Two Objects Collide

    I'd like to know which methods I could use to reduce the loss of kinetic energy when two iron balls collide, or when a plastic ball collides with the floor after a free fall. I have tried to cover the floor with a fabric that would make it more elastic, but it had a small effect (if it hat...
  27. H

    Find the change in the Kinetic energy of an Ideal Gas

    Homework Statement Let 3/2kT be the kinetic energy of ideal gas per molecules. T the absolute temperature and N the avogadro number. Answer the following questions : 1) when the volume doubled at constant temperature. How many times the kinetic energy per molecule become greater than before...
  28. E

    How kinetic energy is proportional to velocity squared

    I hear somewhere explanation why kinetic energy is proportional to $v^2$ and not to $v^3$, for instance. https://www.physicsforums.com/threads/quadratic-forms-and-kinetic-energy.826884/ I wish to find reference for this. Now I find your thread with the same question and very similar answers...
  29. Suyash Singh

    Projectile motion, potential and kinetic energy

    Homework Statement https://www.physicsforums.com/attachments/upload_2018-4-29_12-40-30-png.224871/ Homework EquationsThe Attempt at a Solution 1/2mv^2=10 1/2m(ucos60)^2=10 1/2mu^2/4=10 mu^2=80 what to do now?
  30. E

    Finding the Kinetic Energy using the mass, radius and initial KE

    Information Given:Zero, a hypothetical planet, has a mass of 4.2 x 1023 kg, a radius of 2.8 x 106 m, and no atmosphere. A 10 kg space probe is to be launched vertically from its surface. Question: (a) If the probe is launched with an initial kinetic energy of 5.0 x 107 J, what will be its...
  31. T

    Kinetic energy of an alpha particle

    Homework Statement During the ##\alpha## decay of ##^{238}_{92}U## an ##\alpha## particle is fromed inside the nucleus. Given that the last 4 nucleons in ##^{238}_{92}U## have an average binding energy per nucleon of ##6.1MeV##, estimate the kinetic energy of the ##\alpha## particle when it is...
  32. physicsquestionboi

    Kinetic Friction Homework Help

    A steel washer is suspended inside an empty crate from a light string attached to the top of the crate. The crate slides down a long ramp that is inclined at an angle of 37 above the horizontal. The crate has mass 154 kg. You are sitting inside the crate; your mass is 61 kg. As the crate is...
  33. D

    Change in the Kinetic Energy of a System

    The question is to find the change in kinetic energy of a system. the system in use is a pully system with a wooden block on a flat surface attached to a 100g mass. I have calculated force of friction between the block and desk, and using a ticker timer, I have individual speeds at every 0.1 of...
  34. F

    Coefficient of kinetic friction lab

    Homework Statement I need to find the coefficient of kinetic friction from a set a lab data that I found. I had a mass connected to a mass hanger by a pulley, and measured the acceleration of the mass with various amounts of mass on the hanger. In the attached image, the acceleration was...
  35. Phantoful

    Bead on a string, find y(x) if horizontal velocity is const.

    Homework Statement Homework Equations K = (1/2)mv2 U = mgh W=Fd Integration/Calculus The Attempt at a Solution I'm not sure what I should be doing for this question, if height changes how is it possible that velocity stays the same, according to the conservation of energy (frictionless wire)...
  36. F

    Kinetic Energy Needed for Proton Acceleration

    Homework Statement a) Calculate the kinetic energy required to accelerate a single proton from a rest position to 0.9999c. The mass of a proton is 1.67*10^-27 kg. b) Find the ratio of the kinetic energy to the energy of a proton at rest. c) Explain why no particle accelerator will ever be able...
  37. Amitayas Banerjee

    Kinetic energy as seen from a different frame

    Homework Statement A mass m is initially at rest. A constant force $F$ (directed to the right) acts on it over a distance d. The increase in kinetic energy is therefore $Fd$. Consider the situation from the point of view of someone moving to the left at speed $V$ . Show explicitly that this...
  38. E

    Calculating Change in Kinetic Energy for a Collision on a Frictionless Air Table

    Homework Statement On a frictionless, horizontal air table, puck A (with mass 0.250 kg ) is moving toward puck B (with mass 0.360 kg ), that is initially at rest. After the collision, puck A has a velocity of 0.125 m/s to the left, and puck B has velocity 0.655 m/s to the right. I already...
  39. J

    Split Kinetic and Potential Term in Action in Independt. Var

    Homework Statement [/B] I have the following expression: $$S=T+V$$ $$T=\frac{m}{\tau_0+it}((x_1-x_0)^2+(x_2-x_1)^2)+\frac{m}{2(\tau_1-it)}(x_2-x_0)^2$$ $$V= \frac{(\tau_0+it)}{2}(\frac{k_0 x_0}{2}+\frac{k_0 x_2}{2}+k_0 x_1)+(\tau_1-it)(\frac{k_1 x_0}{2}+\frac{k_1 x_2}{2})$$ The main goal...
  40. L

    Kinetic energy in electron volts

    Homework Statement How much kinetic energy is in electron volts? Homework Equations Kinetic energy = 1/2 mv2 1 electron volt = 1.6 x 10-19 J The Attempt at a Solution [/B] It's a bit unclear to me what the question is asking, since no context at all is given. It's one of the questions in...
  41. almosthavoc

    Very quick question regarding work and kinetic energy

    Homework Statement The question gave a force applied on a block as well as a distance. It also gave the work done by friction which was negative. The question was to find the change in kinetic energy.Homework Equations Wnet = change in KE The Attempt at a Solution I found the work done by the...
  42. T

    Kinetic & Potential Energy of 0° Ice/Water: Examined

    Hi. In all of my question, I mean degrees celsius when I say degree. Think we have a 0 degree ice. we give some energy to it (by a heater) and all of it get into a 0 degree water. How does the kinetic and potential energy of the molecules change? In the book in which I saw this question, it...
  43. M

    Kinetic Energy Equations in MS Excel

    Homework Statement I am having trouble with Microsoft Excel formulas to obtain the correct data for Kinetic Energy 2 initial, KE1 final, KE2f, KEi, KEf, total KE and total KE% Homework Equations Microsoft office uses equations such as =(A2+B2) and I need to determine what is the appropriate...
  44. Z

    The coefficient of kinetic friction for a Ford Focus

    Hi guys, Yesterday I sat down, and just for fun, decided to calculate the coefficient of kinetic friction for the all electric Ford Focus. I keep getting the wrong answer, and it is driving me crazy. Here are the facts. Battery: 23 kWh. Curb weight: 1,651 kg. Maximum travel distance before a...
  45. K

    Lifting an object, kinetic energy, work and forces

    Homework Statement From a physics multiple choice test: "A car is raised to a height of 10 meters. The car is at rest both before and after it has been lifted. The mass of the car is 900 kg. The total work that has been done on the car during the move is" (The right answer is: zero). Wnet...
  46. Boltzman Oscillation

    Finding Lagrangian for Overhanging String on Frictionless Table

    Homework Statement B is 10kg C is 20kg can I find a lagrangian for this system? If so how? Diagram: http://imgur.com/j811rzw Homework Equations L=T-V Kinetic = .5mv^2 Potential = mgh The Attempt at a Solution I know the kinetic energy must be 0 right? How could I find the potential?
  47. S

    Help me find my error in a relativistic kinetic energy calculation

    Hi everyone. Given: an asteroid with the mass of 50,000,000 kg, which is moving with the velocity of oh-my-god particle -- 99.99999999999999999999951% of c. Due to relativistic effects, its total kinetic energy will be 1.44 E+36 Joules (Lorentz factor = 3.2 E+11). A hypothetical particle...
  48. lc99

    Is my reasoning correct? (rotational kinetic energy)

    Homework Statement Homework Equations L = IW RKE = .5IW^2 The Attempt at a Solution Since the two solid spheres have equal radii and same angular momenta, except that the mass differs, i think that the inertia is equal. However, since sphere A is more heavy, it would spin slower than sphere...
  49. S

    Kinetic energy, size of object, and force applied

    Kinda looking to confirm what I already suspect. All things being equal, if two objects have the same kinetic energy, does the fact that one is larger and heavier than the other (although at a slower velocity) mean anything? Specifically when comparing bullets. One bullet .451" in diameter...
  50. B

    Finding the coefficient of kinetic friction on an incline

    << Mentor Note -- Two threads on the same subject have been merged >> I am a junior enrolled in IB Physics at the standard level at my high school. As a part of the curriculum we must perform an Internal Assessment (IA) which involves performing an experiment and performing calculations and it...
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