What is Energies: Definition and 314 Discussions

In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.
Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.
Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth.

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  1. E

    I Energies of bound state for delta function potential

    Hi Let's consider a potential of the form The Schrodinger equation reads as shown in the book 'Introduction to Quantum mechanis' by D.J. Griffiths, Chaper 2 Section 5, the solution of the equation yields (only for bound state, which means E<0): My question: if i have one particle and i apply...
  2. Graham87

    Troubleshooting nuclear decay, electron binding energies, internal contributions

    How do you know which binding energy shell to use? In the solution it uses K and L2. Why specifically L2 and not L3 or L1 for example? And what should I do with the information to omit electrons lower than 20kev? I initially thought that meant to omit the electron binding energies lower than...
  3. emilmammadzada

    Particles produced and energies in the target Geant4

    Dear experts.Which example file in Geant4 can I use to find the particles and energies produced in the target?
  4. G

    Understanding Bond Energies: X-Y Bond Energy Contribution

    Hello. Could someone please help me with this question about bond energy from an MIT course: "For two bonded atoms X and Y, a small X and large Y will result in a bond energy (E A-B) with a large __________ contribution." Thanks a lot if someone can help.
  5. B

    Statistical physics, using the ideas of Fermi Energies, etc. for a star

    a) V=(4/3)pi(r^3) N=M/m_n (M=mass of neutron star, m_n=mass of neutron) Subbed into E_f = (hbar^2 / 2m) (3(pi^2)N / V)^(2/3). T_F = E_F / k_B b) dU = (dU/dS)_s dS + (dU/dV)_s dV p = -(dU/dV)_s dV V=(4/3)pi(r^3) -> r = cubedroot(3V/4pi) subbed into U_g = -(3/5)(G M^2 / r) take (dU/dV) plug into...
  6. N

    A Typical binding energies of sigma-orbitals

    I'm interested in typical electron binding energies of conjugated materials such as pentacene. The carbon 1s energy is easy to find in literature (-285 eV), typical 2π and 2π* binding energies are in the range of few eV (-10 eV ... -2 eV) depending on the size of the conjugated system. But...
  7. SchroedingersLion

    A Calculate the distribution of energies from momenta

    Greetings! I started working through a book of statistical mechanics, and I struggle with properly deriving a formula that makes intuitive sense. I will describe the situation and then my own solution attempts. Suppose we have two systems ##j## and ##k## of volumes ##V_j## and ##V_k## and...
  8. M

    A Just standard model and gravity, up to high energies? An update

    A recurring topic in particle physics, is the possibility of a "desert" above the electroweak scale: no new physics (new particles, new forces) until the grand unification scale or the Planck scale. It's important to remember that the Higgs boson mass was correctly predicted three years in...
  9. 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...
  10. P

    I Fictitious forces and their associated energies

    I understand the idea of a fictitious force. What I am confused about is the energy/potential associated with it. For example, if a cylinder of water is rotating, there apparently exists this centrifugal potential energy, which is obtained by integrating mrw^2 dr. Why is it that the...
  11. AN630078

    Alpha, Beta and Gamma Energies

    Well, gamma photons are pure energy, so surely a gamma photon would have the most energy since gamma-ray photons generally have energies greater than 100 keV. An alpha particle has the highest ionising power of the three on account of its mass, it roughly has a kinetic energy of 5 MeV, whereas...
  12. 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.
  13. L

    Circular Motion Questions (energies, forces, angular velocities, etc.)

    Question 1: I believe that the ratio would be b. 8:1 because by combining the formula for kinetic energy and momentum the expression Ek=p^2/2m can be obtained. Thus, for a body of mass 2kg with twice the momentum: Ek=2^2/2*2=1 For a body of mass 4kg with half the momentum: Ek=1^2/2*4=1/8...
  14. F

    Annihilation: calculation of photon energies

    I set up this problem this way: ##p_a^{\mu}=(E, \sqrt{E^2-m^2}, 0, 0)## ##p_b^{\mu}=(m, 0, 0, 0)## ##p_c^{\mu}=(2E_\gamma, 2E_\gamma, 0, 0)## I have chosen to consider the two photons as a single particle of energy equal to ##2E_\gamma##. At this point I applied conservation of the...
  15. L

    I Hydrogen atom: Energies and eigenstates

    When we say energy levels of the hydrogen atom. Are that energies of the atom or of an electron in the atom? Also corresponding states? http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydwf.html Why energies are negative? E_n \propto \frac{-1}{n^2}
  16. M

    Beta Minus and Beta Plus Decay Disintegration Energies

    I am confused about the disintegration energies of beta minus and beta plus decay. Regarding beta minus decay, the textbook says that "the number of electron masses has been accounted for in Equation (12.38)." What does that mean? Usually the disintegration energy is simply the mass of the...
  17. peguerosdc

    In 2 consecutive decays, determine max and min energies for a particle

    Hi! Instead of just describing my procedure and all my derivations, I really just want to ask if my approach makes sense (actually I have 2 options) to calculate the maximum energy. I am considering c=1 and the problem suggests to consider the neutrino massless: For the first decay, ##Z...
  18. mfb

    A Dark matter experiment XENON1T sees an excess at low energies

    Press release arXiv ~3.5 sigma significance and it could be caused by tritium contamination - although it's unclear where the tritium would come from. If it is really new physics then solar axions or a magnetic moment of neutrinos would fit well. The key plot, figure 5 in the arXiv version...
  19. T

    Calculate the bond-dissociation energies and entropy of a molecule

    If we know the molecular structure of a complex chemical (organic), can we calculate the dissociation energy for each and every bond somehow? Also, can we calculate the standard etropy of the same molecule? These information would be needed to calculate Gibbs free energy for reactions of a...
  20. E

    "External" potential energies strike back

    Goldstein, the oracle of classical mechanics, says: But Morin also reliably tells me that These two definitions contradict in their treatment of external conservative forces. Morin only counts the action of internal conservative forces in the definition of the potential energy of the...
  21. J

    How can hydrogen gas can be made to emit photons of different energies

    This above is the diagram I'm not too sure about the solution to this problem as to why I came here. Is it something to do with photons having different frequencies i.e emitting different amounts of energy based on its frequency
  22. J

    How do atoms emit different photon energies?

    Summary:: Based on this diagram can someone explain how atom of hydrogen gas can be made to emit photons of different energies?
  23. N

    Chemistry Calculating delta H of reaction using bond energies?

    Hi, I have been stuck for hours, i do not understand how i am supposed to use bond energy values for this question like it asks when bond energy values are for molecules in the gas state. The first molecule reactant is a liquid and the second reactant has resonance. I have 0 idea how to approach...
  24. S

    Do photons of different energies interact with each other?

    According to this link photons can interact with each other through the creation of other particles. My questions are do they have to have the same wavelength to be able to interact with one another? Is there a threshold where they start to interact with each other?
  25. E

    B Rest energies of individual nucleons considered in isolation

    I'm conscious I posted a question about a similar topic recently, however I can't seem to resolve an apparent contradiction. As an example, consider a deuterium atom with 1 proton and 1 neutron. When separated at infinity, each has a certain mass and a certain rest energy differing only by a...
  26. mfb

    A Binding energies with muonic structures

    Summary: Could a hierarchical structure of protons, muons and positrons be stable without the weak interaction? This discussion started here, I quote the relevant previous comments and then reply: @Vanadium 50: (mu- e+) is muonium, not true muonium - it is hydrogen-like where the muon...
  27. geoelectronics

    Are electronic and nuclear binding energies a + or - number?

    Please explain the difference between mass deficit and nuclear binding energy and is there a relationship? Thanks Geo
  28. C

    I RC charging - intuition behind equal dissipated energies?

    Assume that a resistor R charges a capacitor C, whose other terminal is connected to the ground. The charge at time t = 0 is assumed to be null and the supply voltage is equal to V. We have, as is well known, ##i = \frac{V}{R} e^{-\frac{t}{RC}}##. Integrating ##\frac{i^2}{R}## between t = 0 and...
  29. C

    Relativity - energies of particles in circular motion

    Summary: What is energy of proton, deuteron and alpha particle in circular motion of the same radius. Hello, I have a problem. Here is the content of an exercise: In some experiment, proton with energy of 1MeV is in circular motion in isotropic magnetic field. What energies would have...
  30. RicardoMP

    How to determine particle energies in center of momentum frame?

    That said, my approach was to determine the energies and 3-momenta at the center of momentum reference frame for each particle, with a fixed s, and check it corresponds to each one of the above, but I'm having some trouble proving that, for example, E_A=\frac{s+m^2_A-m^2_B}{2\sqrt{s}}. I've...
  31. S

    Swinging Ball at Top of Circle: Forces & Energies

    A 0.160 kg ball attached to a light cord is swung in a vertical circle of radius 70.0 cm. At the top of the swing, the speed of the ball is 3.26 m/s. The centre of the circle is 1.50 m above the floor. a. Draw a free-body diagram of the forces on the ball at the top of the swing. b. Calculate...
  32. K

    I The allowed energies of a 3D harmonic oscillator

    Hi! I'm trying to calculate the allowed energies of each state for 3D harmonic oscillator. En = (Nx+1/2)hwx + (Ny+1/2)hwy+ (Nz+1/2)hwz, Nx,Ny,Nz = 0,1,2,... Unfortunately I didn't find this topic in my textbook. Can somebody help me?
  33. P

    Finding the quantized energies of a particle

    Homework Statement Okay, so the question I'm trying to solve is to find the quantized energies for a particle in the potential: $$V(x)=V_0 \left ( \frac{b}{x}-\frac{x}{b} \right )^2$$ for some constant b. The Attempt at a Solution I am following along with the derivation of the quantized...
  34. P

    Calculate the energies of all 4 states up to 2nd order

    Hi, I'm dealing with the following problem. I hope someone could help me with it. Problem is about 2 interacting particles (spin: 1/2 each), with Hamiltonian Ho=-A( S_1z + S_2z) and perturbation H1={(S_1x)*(S_2x) - (S_1y)*(S_2y)}. The question asks to calculate the energies of all 4 states up...
  35. Zypheros_Knight

    B E- p+ collision product energies

    Greetings! This is probably the most simplest of questions but I wanted to ask that which particle carries most of the energy of an electron-proton collision (as in p + e− → n + νe), the neutron or the neutrino? What happens if we use a higher energy proton or electron? For example we use...
  36. R

    A Mass of Higgs, W and Z bosons going to zero at high energies

    Hi Everyone! Hope everyone is really enjoying pushing the Physics frontiers! Really need some help here. In the Electroweak sector of the Standard Model, it is apparently the case that the success of renormalisation to remove the Ultraviolet Divergence relies on the fact that at high energies...
  37. MichPod

    I Why the Lagrangian is the difference of energies?

    The Lagrangian in classical mechanics is known to be a difference of the kinetic and potential energy. My first question is - why? I.e. are there any reasons (except for "because it works this way") to have it as this difference of energies? The second question is why is it this very value...
  38. ohwilleke

    I Proton Decay At The Highest Possible Energies

    Proton decay has not been observed and has been constrained to be extremely rare in ordinary low temperature situations, if it happens at all (the Standard Model says it doesn't happen at all, because there are no lighter decay products that would not violate conservation of baryon number)...
  39. Matt Chu

    Potential Energies of Two Charged Cylinders

    Homework Statement Problem 1.24 (this is unimportant; it's just a different way of calculating the potential energy of a solid cylinder) gives one way of calculating the energy per unit length stored in a solid cylinder with radius a and uniform volume charge density ##\rho##. Calculate the...
  40. A

    Vertical spring, the relationship between potential energies

    I'm stuck with a solution to the vertical spring with a body suspended. The solution says that when the body's gravitational potential energy is decreasing, the spring's potential energy must be increasing. How is this correct? I understand the analysis leading to the result that the vertical...
  41. PhilQ

    A Tunneling Electron Energies

    If we have a MIM device of Ti/Nb2O5/Ti at room temperature (300K), with a measured barrier height(s) of 0.0eV, the insulator thickness is say 2nm, and let's call the electron affinity of Nb2O5 4eV, and the Work function of Ti 4eV (for the sake of a simplified question), what is the average /...
  42. A

    I IR divergences and total energies....

    I've done some recent reading on IR divergences (propagators becoming singular, etc.). I believe I understand collinear divergences (to some extent)... but I'm not sure about total energies for (primarily) soft photons. In all scattering experiments, total energy should be conserved - but if...
  43. L

    Question about Calculating Bond Energies

    Homework Statement Part of a chemical equation, but i had to calculate the bond energies in C2H6, Homework Equations im given that C-H bonds are 414 kj/mol[/B]The Attempt at a Solution and that i know there are 6 of these based on the lewis structure, but how come i don't have to include C-C...
  44. W

    Thermodynamics: Free Energy Confusion

    Homework Statement Hi all, I'm having quite a big problem trying to understand the concept of enthalpy and free energy. I feel that a good way to sort this out is to write out what I understand about these things and have people correct me. Thanks in advance for any assistance. I'm learning...
  45. G

    I Gamma radiation, photon energies and wavelength question

    I haven't though about this from such a perspective but today while reading wikipedia (yes yes not the best source) I got confused, now the "eV" is said to measure the energy gained by an electron between a potential difference of 1V. I assume particle physicists use this measurement because its...
  46. 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...
  47. L

    Need help finding fermion energies and probabilities

    <Moved from a technical forum, therefore no template> For two non-interacting fermions confined to a 1d box of length L. Construct the antisymmetric wave functions (Slater determinant) and compare ground state energies of two systems, one in the singlet state and the other in the triplet state...
  48. BookWei

    Find the possible total energies (Quantum Physics)

    Homework Statement I'm doing problems for practice in quantum physics. Consider two particles of the mass m in one dimension with coordinates being denoted by x and they are connected by a spring with spring constant k. Suppose that the total momentum of the system is p. Find all possible...
  49. V

    Eigenvectors of Ly and associated energies

    Homework Statement Consider a particle with angular momentum l=1. Write down the matrix representation for the operators L_x,\,L_y,\,L_z,for this particle. Let the Hamiltonian of this particle be H = aL\cdot L-gL_z,\,g>0.Find its energy values and eigenstates. At time t=0,we make a measurement...
  50. L

    Electron's energies and charge density in plate-capacitor

    Homework Statement Tasks to do: a.)give voltage b.)give the absolute value of charge density for plates Presumably the absolute values of charge densities for plates is equal between the two of them. An electron is accelerated in a homogenic electric field, inbetween two oppositely charged...