What is Enegy: Definition and 12 Discussions

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The various mechanisms of energy transfer that define heat are stated in the next section of this article.
Like thermodynamic work, heat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of state, for example its internal energy, or for example its enthalpy. This is to be distinguished from the ordinary language conception of heat as a property of an isolated system.
The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. Such methods are called calorimetry.
The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy (being transferred), the SI unit of heat is the joule (J).

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  1. M3D1

    B To confirm if I am correct about the role of voltage in a circuit

    i just finished some basic concepts about electricity and wanted to confirm if my deduction/understanding is correct: in a simple circuit of let's say a battery and lamp,motor,resistor, the difference between potential of two ends of battery(voltage) say how much potential energy per charge has...
  2. Raz Matazz

    I Why do electrons always move?

    Whether in vacuum inside a CRT, or in a metal, a potential difference has to be applied for free electrons to move from the negative to the positive terminal. However, the reality is that free electrons are still moving when no voltage is present at the 2 ends of a metal conductor. In this...
  3. giveortake

    Calculating the work done from an equation for variable force

    Homework Statement The force on a particle is directed along an x axis and given by F = F0(x/x0 - 1) where x is in meters and F is in Newtons. If F0 = 1.5 N and x0 = 4.9 m, find the work done by the force in moving the particle from x = 0 to x = 2x0 m. Homework Equations F = force, w = work, x...
  4. G

    Energy Confusion (Conservation of Energy?)

    Anyone know if the following statement is true (and why)? "Getting to higher ground would increase his gravitational potential energy, decreasing the effects of non-conservative forces, which would allow him to move easier." CLARIFICATION: "move easier" refers to a lack of friction and not the...
  5. Sebastiaan

    A How to calculate the energy of Gamma rays in fusion

    Lets say you have your basic fusion reaction D + H → He3 + γ + 5.49 MeV Now exactly how much of the energy is carried away by the gamma ray and how much by the Alfa particle ?
  6. ChloeYip

    Gas Kinetic Energy: Monatomic or All Gases?

    "KE=3/2nRT=3/2kT" is applicable to only monatomic gas or all kind of gas? What about " KE=1/2*fkT" ? (f: degree of freedom) Is it implies the same thing as "KE=3/2nRT=3/2kT" ? Thank you.
  7. J

    What is the significance of U at infinity in relation to Earth?

    hello sir ...can anyone explain me the value of (U) at infinity with respect to Earth as reference point
  8. N

    Calculating Initial Kinetic Energy for Alpha Particle Approaching Nickel Nucleus

    Homework Statement What initial kinetic energy must an alpha particle have if it is to approach a stationary nickel nucleus to within a distance of 24.6 fm? Homework Equations not sure The Attempt at a Solution I'm not really sure how to connect the KE with the distance of the...
  9. V

    Cannot see where potential enegy comes from in classical mechanics

    Homework Statement F=force, a=acceration, m=mass, U potential energy, P momentum, E=energy How do derive 2 and 3 from 1( see below). Homework Equations 1) F=ma, 2) E= (p^2)/(2m) + U, 3) ma = -del U The Attempt at a Solution I try to understand why U pop into the...
  10. D

    Pile driver - Conservation of enegy

    Hi, I did some calculations but somehow I feel it's not 100% correct. Could someone have a look please. Many Thanks "Task" A pile driver of mass mh has struck a pile of mass mp and driven the pile D meters into the ground, if the velocity of the strike is V, determine the force due to...
  11. R

    Zero Point Energy: Exploring the Material Universe

    I was wondering if my thought on Zero Point Field was correct. First of all is it part of the material universe? Second, is it kind of like an ether or mediam through which things move through?
  12. H

    Momentum, enegy and collisions

    A proton (mass 1 u) moving at 7.80 x10^6m/s collides elastically and head-on with a second particle moving in the opposite direction at 2.40x10^6 m/s. After the collision, the proton is moving opposite to its initial direction at 6.60x10^6m/s. Find the mass and final velocity of the second...