The Fundamental Laws of Nature/Mass-Energy and the Laws of Thermodynamics and Related Definitions
SPEAKING Enquiry Force or Forcing is a process  of exchanging useful-energy (forced displacement) with net-zero exchange at forced equilibrium. The Second Law provides conditions and limits for process forcing (energy exchange direction and limit).

Energy Pyramid * Second Law (or The 2nd Law)* ZerothReligion.mkostic.com * Kostic's Keynote in China
... click to enlarge ...
"Nothing occurs locally, nor globally in the universe, without mass-energy exchange/conversion and entropy production. It is crystal-clear (to me) that all confusions related to the far-reaching fundamental Laws of Thermodynamics, and especially the Second Law (Abstract & FULL paper), are due to the lack of their genuine and subtle comprehension." > Sadi Carnot's Reflections <*> Clausius Theory of Heat < Elusive Nature of Entropy
The miracles are until they are comprehended and understood. Perpetual Motion Machines (PMMs) Nature of Thermal and Mechanical Energy Transfer
If all energy is literally expelled from a confined space, then nothing, empty space will be left. As long as any matter is left it will contain the energy - even at zero absolute temperature the electrons will be orbiting around very energetic nucleus. Matter is and must be energetic, E=mc^2, thus literally, "energy is everything," no energy, nothing in the space. The mass and energy (internal motion in all-directions without resulting momentum in one direction, like nuclear, chemical and thermal) are manifestation of each other and are equivalent; they have a holistic meaning of mass-energy. In addition to internal energy (i.e., 'balanced' motion in all directions which results in zero momentum that give rise to the gyroscopic inertia in all directions, i.e. inertial mass), the bulk mass may have energy related to its directional (thus bulk) linear or rotational motion (momentum).
A fundamental law is either valid or not, cannot be selectively valid, then it is not a universal law
! Note that due to thermal radiation the Sun is loosing commensurate mass (which could be observed/measured), and so  are other energy transfers regardless how small or if non-observable.

Stretching the mind further: Therefore, mass may be a special, zero-order tensor-like quantity due to "over-all-isotropic in all-directions" motion and interactions of elementary particles (that make up its structure) and thus give rise to inertia if accelerated in any direction, i.e., resisting change of motion in any and all directions with equal components (the zero-order, isotropic mass inertia). There may be anisotropic masses, with bulk linear or rotational motion, being the extreme cases. Note that fundamental particles (without inertial mass, like photons and similar, but with relativistic masses E/c^2) has to always move with ultimate speed of light in vacuum, and such particles (some yet to be discovered) might be moving (orbiting with twisting, string-like vibration and rotation) within virtually infinitesimal spaces and thus making-up other "massive" so-called elementary particles.
More at: www.kostic.niu.edu * PUBLICATIONS/Presentations * Energy&Environment * Industrial Research - CONSULTING
YES! Thermodynamics, a science of energy, and the Mother of All Sciences will provide vision for the future energy solutions: Insulation (to minimize losses), Regeneration (to recover losses), Cogeneration (to minimize irreversibility), and Conservation with Optimization (to increase efficiency).

CLICK to Enlarge ...Energy Provides Existence and is Cause for Change (hopefully sustainable progress and happiness!): Energy is possessed (thus equilibrium property) by material systems and redistributed (transferred) between and within system(s), due to systems' non-equilibrium, via forced-displacement interactions (process) towards the equilibrium (equi-partition of energy over mass and space); thus energy is conserved (the 1st Law) but degraded (the 2nd Law). Effects are consequences of Causes except at Equilibrium they are equal (reversible).  The existence in space and transformations in time are manifestations of perpetual mass-energy forced displacement processes: with net-zero mass-energy transfer in equilibrium (equilibrium process) and non-zero mass-energy transfer in non-equilibrium (active process) towards equilibrium. System components (particles and bodies) that exert forces have to be massive (2nd Newton Law) and with accompanying reaction forces (3rd Newton Law). See also Mass-energy transfer and PMMs

The Grand Law of Nature: During any process mass-energy is exchanged and conserved, while entropy is irreversibly produced. The universe consists of local material (mass-energy) structures in forced dynamic-equilibrium and their interactions via forced fields. The forces are balanced at any time (including inertial - process rate forces) thus conserving momentum, while charges/mass and energy are transferred and conserved during forced displacement in space all the times, but energy is degraded (dissipated) as it is redistributed (transferred) from higher to lower non-equilibrium potential towards equilibrium (equi-partition of energy)-(by M. Kostic)

<< Click to enlarge  *>>Definitions >>*http://goo.gl/sH9ni>Images(and)

The phenomenological Laws of Thermodynamics have much wider, including philosophical significance and implication, than their simple expressions based on the experimental observations – they are The Fundamental Laws of Nature: The Zeroth (equilibrium existentialism), The First (conservational transformationalism), The Second (irreversible-directional transformationalism), and The Third (unattainability of 'emptiness'). They are defining and unifying our comprehension of all existence and transformations in the universe. The forces, due to non-equilibrium of mass-energy in space (non-uniform ‘concentrations’), causing the mass-energy displacement, thus defining the process direction, are manifested by tendency of mass-energy transfer in time towards common equilibrium. It should not be confused with local creation of non-equilibrium and/or ‘organized structures’ on expense of ‘over-all’ non-equilibrium, by spontaneous and irreversible conversion (dissipation) of other energy forms into the thermal energy, always and everywhere accompanied with entropy generation (randomized equi-partition of energy per absolute temperature level). The fundamental laws of nature are considered to be axiomatic and many believe they could not be explained, proven or questioned. However, everything may and should be questioned, reasoned, explained and possibly proven. The miracles are until they are comprehended and understood.


There is ‘energy or 'mass-energy' as the building block of existence, which is conserved while transferred during forced interactive displacement (subject of the First Law of Thermodynamics: energy cannot be destroyed nor generated from nowhere); and, there is ‘useful energy or 'work potential' as the measure of non-equilibrium (an autonomous concept), which is the cause-and-effect of forcing energy transfer from higher to lower energy density/potential (subject of the Second Law of Thermodynamics: non-equilibrium is irreversibly dissipated in time towards equilibrium and cannot be generated from nowhere, i.e., the useful work potential is irreversibly converted to heat, and thus entropy is always generated and only in limit conserved but cannot be destroyed, the latter not to be confused with local entropy decrease on the expense of increase elsewhere.
  During forced energy transfer a part (and ultimately all) of the useful energy is dissipated (irreversibly converted into the thermal energy with the corresponding entropy generation), but in limit, the non-equilibrium (work potential) may be conserved during reversible processes, including localized increase of energy density/potential on the expense of decrease elsewhere (forcing advantage)
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►All interactions in nature are physical and based on simple cause-and-effect conservation laws, thus deterministic and should be without any exceptional phenomenon. Due to diversity and complexity of large systems, we would never be able to observe deterministic phenomena with full details but have to use holistic and probabilistic approach for observation; therefore, our observation methodology is holistic and probabilistic, but phenomena have to be deterministic, not miraculous nor probabilistic.
►There is no proof that an electron, or any other elementary particle, has or does not have a structure. The concept of elementary particle is intrinsically problematic (
just because we cannot observe or reason a structure which exhibits certain phenomena, does not mean it does not exist). Past and recent history proved us to be wrong every time. Particularly problematic is the current theory which requires elementary particle annihilation/creation (“miraculous creationism”) while using conservation laws. At the very least (in phenomenological view) the elementary particles should be conserved and be the building structure for other particles and systems.
Note that many concepts (in modern physics) are "virtual" entities that are part of the mathematical theory, but are not directly observable.
T
here is no such thing as a unidirectional force or a force that acts on only one body (no imaginary boundary vector-forces). Put it very simply: a forcing (force-flux cause-and-effect phenomena) acts between an interface of pair of objects (forced interaction: action-reaction, including process-inertial forces), and not on a single object. The Newton Laws and the Laws of Thermodynamics imply that all forces are mass-energy interactions (forced displacements with momentum and energy transfer and conservation) between different particulate bodies due to non-equilibrium (available energy or work potential, cause of forcing) towards the equilibrium.

All matter must be somewhat elastic (can be compressed or stretched). If bodies could be perfectly rigid we'd have infinite forces acting with infinite speeds for infinitesimal times (if you pushed on one end of a perfectly rigid stick, the other end would move instantaneously). System components (bodies) that exert forces have to be massive (2nd Newton Law) and with accompanying reaction forces (3rd Newton Law).


Definitions in alphabetical order: Absolute_Zero_Temperature * Energy * Entropy * Equilibrium or Structure * Exergy * Forced_Field * Heat * Ideal_gas * Interaction  * Interface_boundary * Internal_Thermal_Energy * Internal_(Total)_Energy * Isolated_system *  Mass * Mechanical_Energy * Motion * Relativity * Temperature *Temperature, Absolute_Zero * Thermal_Radiation * System * Work

Definitions in logical order: System * Energy * Mass * Forced_Field * Motion * Interaction * Structure_or_Equilibrium * Relativity * Interface_boundary * Isolated_system * Ideal_gas * Work * Exergy * Mechanical_Energy * Temperature * Heat * Internal_Thermal_Energy * Internal_(Total)_Energy * Absolute_Zero_Temperature * Entropy * Thermal_Radiation


DEFINITION of ENERGY: "Energy is a fundamental property of a physical system and refers to its potential to maintain a material system identity or structure (forced mass-energy field in space) and to influence changes (via forced-displacement interactions, i.e. systems' re-structuring) with other systems by imparting work (forced directional displacement) or heat (forced chaotic displacement/motion of a system molecular or related structures). Energy exists in many forms: electromagnetic (including light), electrical, magnetic, nuclear, chemical, thermal, and mechanical (including kinetic, elastic, gravitational, and sound) ... Energy is the ‘‘building block’’ and fundamental property of matter and space and, thus, the fundamental property of existence. Energy exchanges or transfers are associated with all processes (or changes) and, thus, are indivisible from time." (by M. Kostic).  NOTE If all energy is literally expelled from a confined space, then nothing, empty space will be left. As long as any matter is left it will contain the energy - even at zero absolute temperature the electrons will be orbiting around very energetic nucleus. Matter is and must be energetic, E=mc^2, thus literally, "energy is everything," no energy, nothing in the space. The mass and energy are manifestation of each other and are equivalent; they have a holistic meaning of mass-energy.

DEFINITION of ENTROPY: Entropy is a thermal displacement (dynamic thermal volume) of thermal energy due to temperature as a thermal potential (dQ=TdS). It is an integral measure of (random) thermal energy redistribution (due to heat transfer and/or irreversible heat generation due to energy degradation) within a system mass and space, per absolute temperature level: dS=dQrev/T=CqdT/T with J/K unit. It may be expressed as being related to logarithm of number of all thermal, dynamic microstates (position and momenta), or to the sum of their logarithmic probability or uncertainty, that correspond, or are consistent with the given thermodynamic macrostate. Note that the meanings of "all relevant adjectives" are deeply important to reflect reality, and as such, "disorder" has metaphoric description for real systems. Entropy is increasing from perfectly-ordered (singular and unique) crystalline  structure at zero absolute temperature (zero reference) during reversible heating (entropy transfer) and entropy generation during irreversible energy conversion (lost of work-potential to thermal energy), i.e. energy degradation or random equi-partition within system material structure and space per absolute temperature level. NOTE that work-potential is preserved (conserved) if the non-equilibrium is preserved (with regard to the common equilibrium), i.e., during reversible processes. FURTHERMORE, entropy of a system for a given state is the same, regardless whether it is reached by reversible heat transfer or irreversible heat or irreversible work transfer. ... see also and The 2nd Law

* The 2nd Law defines forced directional displacement of useful/available mass-energy transfer in time, thus all processes, from higher to lower energy density/potential, due to its non-equilibrium (non-uniformity) in space, towards equilibrium (force-flux cause-and-effect phenomena), while part of the energy (up to the whole) is irreversibly converted to thermal energy (dissipated via heat) and thereby generated entropy, equal to the generated thermal energy per absolute temperature. The process cannot proceed spontaneously in opposite direction against the forcing and thus create non-equilibrium and destroy entropy, however the non-equilibrium (useful energy or work potential which is cause of process forcing) could be re-arranged/transferred and in limit conserved (in reversible processes, including forcing advantage potential). The original Clausius and Kelvin-Plank statements are the special cases related to the thermo-mechanical energy conversions. Due to reversible equivalency of all types of (coupled) energy conversions, all different statements of the Second Law (2nd Law) are equivalent...also...and.

   There is 'energy' (or 'mass-energy' as the building block of all existence) which is conserved while transferred during forced interactive displacement (subject of the First Law of Thermodynamics: energy cannot be destroyed nor generated from nowhere; and, there is 'useful energy' or 'work potential' as measure of non-equilibrium (an autonomous concept) which is the cause-end-effect of forcing energy transfer (all processes) from higher to lower energy density/potential (subject of the Second Law of Thermodynamics: non-equilibrium is irreversibly dissipated/lost in time towards equilibrium and cannot be generated from nowhere, i.e., the useful work potential is irreversibly converted to heat, and thus entropy is always generated, only in limit it may be conserved but cannot be destroyed, the latter not to be confused with local entropy decrease on the expense of increase elsewhere).

    During forced energy transfer a part (and ultimately all) of the useful energy is dissipated (irreversibly converted to thermal energy with the corresponding entropy generation), but in limit, the non-equilibrium (work potential) may be conserved during reversible processes, including localized increase of energy potential on the expense of decrease elsewhere (forcing advantage). See also Perpetual Motion Machines.

There is no such thing as a unidirectional force or a force that acts on one body only (no imaginary boundary vector-forces). Put it very simply: a forcing (force-flux cause-and-effect phenomena) acts between an interface of pair of objects (forced interaction: action-reaction, including process-inertial forces), and not on a single object. The Newton Laws and the Laws of Thermodynamics imply that all forces are mass-energy interactions (forced displacements with momentum and energy transfer and conservation) between different particulate bodies due to non-equilibrium (available energy or work potential, cause of forcing) towards the equilibrium.
►Mass-energy is directionally displaced/transferred from its higher to lower density/potential while conserved in time due to forced displacement caused by its non-equilibrium (non-uniform) distribution in space, in an irreversible process approaching equilibrium until its distribution equalize in all directions (equi-partition of mass-energy).

DEFINITION of The 2nd Law (SECOND LAW) of Energy Degradation: The useful-energy (non-equilibrium work potential) cannot be created from within equilibrium alone or otherwise, it only can be transferred between systems (ideally conserved) and dissipated into thermal energy thus generating entropy.
"Non-equilibrium, i.e., non-uniform distribution of mass-energy in space, tends in time to spontaneously and irreversibly redistribute over space towards common equilibrium, thus non-equilibrium cannot be spontaneously created. All natural spontaneous, or over-all processes (proceeding by itself and without interaction with the rest of the surroundings) between systems in non-equilibrium have irreversible tendency towards common equilibrium - and thus irreversible loss of the original work-potential (measure of non-equilibrium), by converting other energy forms into the thermal energy accompanied with increase of entropy (randomized equi-partition of energy per absolute temperature level)" (by M. Kostic). The spontaneous forced tendency of mass-energy transfer is due to a difference or non-equilibrium in space of the mass-energy space-density or mass-energy-potential. As mass-energy is transferred from higher to lower potential, and thus conserved, the lower mass-energy potential is increased on the expense of the higher potential until the two equalize, i.e., until a lasting equilibrium is established. THAT explains a process tendency towards the common equilibrium and impossibility of otherwise (impossibility of spontaneous creation of non-equilibrium). If a non-equilibrium is preserved "in part or in whole" then the preserved mass-energy transfer is termed as a "work", the "in whole" being the maximum possible or the work potential. In a process the (maximum) work potential will in part or in whole be irreversibly converted (i.e., dissipated via "heat" transfer) into newly generated thermal energy ("randomized" energy) thus generating/increasing the entropy (generated thermal energy per absolute temperature). If, in limit, the dissipated work potential is infinitesimal, then the original non-equilibrium is preserved, i.e., rearranged only, and thus the process could be reversed, in limit again, to the original non-equilibrium -  a reversible process. THEREFORE, it is impossible to produce work from a single thermal reservoir in equilibrium, then a non-equilibrium (stored work potential) will be spontaneously created. FURTHERMORE, the spontaneous creation of non-equilibrium would in time "siphon" or compress all existing mass-energy, in limit, into an infinitesimal space with infinite mass-energy potential singularity, thus contradicting the equilibrium space existence in time. ["Spontaneous" imply "by itself" or "on its own" (including inertial and/or reversible/elastic forcing which may produce local non-equilibrium of one kind on the expense of others); however, the non-equilibrium cannot be created spontaneously, but only maintained and ultimately "lost", i.e., transferred to equilibrium !].

Organization/creation of technical (man-made) and natural (including life) structures and thus creation of "local non-equilibrium" is possible and is always happening in many technical and natural processes while entropy is generated (never destroyed), using another functional structures (channeling/filtering, pumping, tools, hardware/software templates, information-knowledge-"intelligent" templates, DNAs, etc.), HOWEVER, the mass-energy flow/transfer within those structures will always and everywhere dissipate energy and generate entropy (according to the 2nd Law!), i.e. on the expense of internal and/or surrounding/boundary systems' non-equilibrium. It may appear that the created non-equilibrium structures are self-organizing from nowhere, from within an equilibrium (thus violating the 2nd Law), due to the lack of proper observations and "accounting" of all mass-energy flows, the latter maybe in "stealth" form or undetected rate at our state of technology and comprehension (as the science history has though us many times). The miracles are until we comprehend and explain them!


The fundamental “cause-and-effect” concepts and phenomena are often simple, but they are usually manifested in many different forms and are mutually coupled or interrelated. We often need to make different simplifications and idealizations in order to be able to isolate and then understand and analyze the phenomena. Real properties and processes are often coupled and we usually need to idealize and decouple them to focus on one issue and better understand and explain it. For example, any thermal process is coupled with mechanical expansion and vice versa and we may decouple those, like idealizing an isochoric process with heat transfer only, or isentropic process without heat transfer, excluding thermal radiation, etc. We may idealize systems, like ideal gas or incompressible fluid, etc., or boundaries, like ridged, adiabatic, etc., or processes, like frictionless or non-dissipative, quasi-equilibrium or reversible, etc. The emphasis here will be on the thermo-mechanical interactions where the conservation of energy was historically first “stuck” and re-established (The 1st Law of Thermodynamics), however it could be easily extended to other interactions involving electro-magnetic, electro-chemical, or nuclear processes. We will idealize and define the most essential concepts and related nomenclature used in this treatise (in some logical order) as follows:

System (also Particle or Body or Object) refers here to any, arbitrary chosen but fixed material physical system in space (from a single particle to system of particles, occupying system volume within its own enclosure interface or system boundary, separating itself from its surroundings), which is subject to observation and analysis. A system is made of material sub-systems with certain structure or substructure, down to the most fundamental elementary particles that we are not capable of looking further into and consider them to be material points. The elementary particles are “forcibly bound” in larger particles which posses mass and energy in space, thus have dimensions, and are capable to “forcibly bound and or interact” with each other and form larger structures with forced fields in space, and so on. We know that physical systems are made of very small and discrete particles on sub-nucleus, atomic and molecular scale, see Fig. 1, but also may be considered as continuum media, with integrated average particle properties at larger scales.

Energy is a fundamental property of a physical system and refers to its potential to maintain a material system identity or structure (forced field in space) and to influence changes (via forced-displacement interactions, i.e. systems' re-structuring) with other systems by imparting work (forced directional displacement) or heat (forced chaotic displacement/motion of a system molecular or related structures). Energy exists in many forms: electromagnetic (including light), electrical, magnetic, nuclear, chemical, thermal, and mechanical (including kinetic, elastic, gravitational, and sound) ... Energy is the ‘‘building block’’ and fundamental property of matter and space and, thus, the fundamental property of existence. Energy exchanges or transfers are associated with all processes (or changes) and, thus, are indivisible from time. NOTE If all energy is literally expelled from a confined space, then nothing, empty space will be left. As long as any matter is left it will contain the energy - even at zero absolute temperature the electrons will be orbiting around very energetic nucleus. Matter is and must be energetic, E=mc^2, thus literally, "energy is everything," no energy, nothing in the space. 

Mass refers to system measure of inertia (resistance to system acceleration or motion change as a whole). Much of the mass of a nucleon (proton or neutron) resides in form of energy of the gluons which bind quarks into nucleon (not yet fully understood), while the residing energy of photons’ electromagnetic field which bind electrons to nucleus is very small, see Fig. 1. We may postulate, especially after Einstein’s energy-mass correlation, that mass is a kind of spinning energy in all directions within elementary particles which give rise to its inertia, i.e. forced resistance to change of its motion (acceleration) in all directions as an integral particle mass or an integral system mass. Statements about quarks (elementary particles) which make protons and neutrons and their bindings must be taken with a grain of salt, since interactions between elementary particles are not yet well understood, and they are believed to be material points (wit zero dimensions) since their structure is not known (assumed to not have a structure!).

Forced Field refers to “conservative or reversible or elastic” force distribution in space responsible for particle and/or system structure or mass-energy distribution in space: the cause-and-effect phenomena. The binding energy of any structure is “stored” within that structure and represents potential energy which could be partially released if a system structure is transformed. i.e. restructured into another structure, like in nuclear or chemical reactions. Forced field is a displacement gradient of related potential energy of a system.

Motion refers to system (and its structure) activity that manifests in its displacement in space and time, thus defining space coordinates and time. System motion could be resolved into different components as spinning around its center of mass, vibration, rotation around other systems, and linear translation. Spinning and twisting/vibrations around a system’s center of mass may not directly influence interactions with other systems but contribute to that system stored energy and may be a cause-and-effect of the related forced fields. However the translational motion is bound to interact with other systems via collision (also may be enhanced in part by rotation and vibration at the time of collision), and such random motion of system structure (molecular and related substructure) gives rise to temperature (particulate kinetic energy) and pressure (particulate change of momentum rate per unit area in direction normal to the area), and similar, see Fig. 1.

Interaction (also Collision or Process) refers to energy exchange via forced displacement in time between two material systems -- a generalized collision, i.e. a “cause-and-effect” process. Interaction involves and thus define, or inter-define force, mass and motion, the latter being relative space displacement in time with reference to the two interacting systems. We may be lost at the elementary particle scale or sub-scale due to our inability to observe the phenomena with the tools we comprehend (the photons and electromagnetic waves are the finest resolution tools we comprehend now), or we may be lost at the large scale in “curved space” for similar reason. However, we have accumulated a lot of observations in a long time over a large space scale that we could rigorously reason the fundamental Laws of Nature: the Newton's Laws and more general phenomenological Laws of Thermodynamic .

Structure or Equilibrium State (also System Identity State or System Properties) refers to apparently quasi-static structure with sustained macro system properties (which are statistical averages of corresponding micro-structure properties), like temperature, pressure, volume, entropy, energy and others. If an isolated system’s properties are non-uniform, the spontaneous interactions, given enough time, will take place towards equalization of their statistical averages over space and time, and towards uniformity of macro properties which is in effect the maximum probability of all possible microstates for a given macro state, i.e towards an equilibrium state with maximum entropy. For example the random kinetic energy of micro-structure will equi-partition its kinetic energy (i.e. redistribute kinetic energy statistically equally among all its particles) and thus equalize its temperature and pressure, and in turn all other properties.

Relativity refers to properties of a system with reference to other systems or a chosen reference system, since all observations and interactions are between the systems. Our observations and comprehensions of the systems are limited with our existence, including sensing and mental tools, as well as our space and time scales, so that subject of this treatise is referring to phenomenological, thermodynamic properties and interactions, which may be extended inward and outward as long as we are aware of relativity and uncertainty outside of observed extreme space and time scales. As already mentioned, we may be lost at the elementary particle scale or sub-scale due to our inability to observe the phenomena with the tools we comprehend (the photons and electromagnetic waves are the finest resolution tools we comprehend now), or we may be lost at the large scale in “curved space” for similar reason.

Interface Boundary (or Boundary for short) refers to “real” or imaginary boundary surface in space to separate systems or sub-systems or their parts from each other. In reality the interface boundary between the systems is irregular and time-changing surface defined by the interaction forces separating the two systems. If diffusion of one system structure into the other system structure is negligible than the boundary may be idealized as impermeable. Similarly if heat transfer or deformation or any interaction are negligible, we may idealize the boundary as adiabatic or rigid or isolated, respectively, and so on. 

Isolated System refers to a system with an idealized isolated boundary enclosure which does not allow for any interaction with its surroundings. In reality there are no such idealized boundaries since it is impossible to prevent all interactions with the surroundings. Isolated system should not be confused with a system “left alone in the universe,” since such system will spontaneously expend and or radiate into the “empty” universe (there is no “empty” universe either!). A good approximation of an isolated thermo-mechanical system is a thermos or insulated vacuum bottles, or a ridged container with surrounding temperature equal to the system temperature.

Ideal Gas refers to idealization of real gasses at high temperature (high molecular velocities) and low pressure (high separation between the molecules) as if a gas molecules are material points with real velocities and mass but zero space dimension (material points) and without any intermolecular forces. This idealization simplifies the ideal gas molecules’ interactions as random elastic collisions only. Since this idealization provides for convenient analysis of random molecular motion and is not much different from reality, the corresponding kinetic theory of ideal gasses has explained and proved many thermal phenomena (see Fig. 1).

Work refers to controlled energy transfer when one system is exerting force in specific direction and thus making a purposeful change (displacement) of the other systems. It is inevitably (spontaneously) accompanied, to a larger or smaller degree, with dissipative (without control) energy transfer referred to as heat (see below, and for more details in next Section).

Exergy refers to the maximum system work potential (useful energy) if it is reversibly brought to the equilibrium (while interacting ) with reference heat reservoir (surroundings), i.e., exergy is a measure of a system non-equilibrium with regard to the reference surrounding system of infinite capacity. After the system comes to equilibrium with the reference surroundings its exergy is zero (dead state). Exergy is not conserved but is destroyed or lost during real irreversible processes commensurate to the related entropy generation.

Mechanical Energy refers to the energy associated with ordered motion of moving objects at large scale (kinetic) and ordered elastic potential energy within the mechanical structure (potential elastic), as well as potential energy in gravitational field (potential gravitational).

Temperature is a measure (within the scaling constant) of the average kinetic energy related to thermal interaction of disordered microscopic motion of molecules and atoms, i.e., a measure of the representative thermal-microparticle kinetic energy. The concept of temperature is complicated by the particle internal degrees of freedom like molecular rotation and vibration and by the existence of internal interactions in solid materials which can include so called collective molecular or atomic behavior. All of those motions could contribute to the kinetic energy during particle (thermal) interaction. When two objects are in thermal contact (i.e. interaction of random motion of their particles), the one that tends to spontaneously give away (loose) energy is at the higher temperature. In general, temperature is a measure of the tendency of an object to spontaneously exchange thermal energy with other object until their temperatures equalize, that is until their interacting particle kinetic energy equi-partition (statistically equalize).

Heat refers to inevitable (spontaneous) energy transfer due to temperature differences, to a larger or smaller degree without control (dissipative) via chaotic (in all directions, non purposeful) displacement/motion of system molecules and related microstructure, including thermal radiation, as opposed to controlled (purposeful and directional) energy transfer referred to as work (see above, and for more details in next Section).

Internal Thermal Energy refers to the energy associated with the random, disordered motion of molecules and related potential energy of intermolecular forces, as opposed to the macroscopic ordered energy associated with ordered “bulk” motion of system structure at large scale, and excluding internal binding energy within atoms (nuclear) and within molecules (chemical).

Internal (Total) Energy refers to the energy associated with the random, disordered motion of molecules and intermolecular potential energy (thermal), potential energy associated with chemical molecular structure (chemical) and atomic nuclear structure (nuclear), as well as with other structural potentials in force fields (electrical, magnetic, elastic, etc.). It refers to the “invisible” microscopic energy on the subatomic, atomic and molecular scale with net-zero bulk-momentum, as opposed to “visible” mechanical, bulk energy.

Absolute Zero Temperature refers to a system state where the random (thermal) kinetic energy of its structure (molecules if system is made of molecules, or a lattice random vibration if a system is made of crystalline lattice of molecules or atoms, which give rise to the temperature) is zero (see definition of temperature above). However the motion within the system structure (binding motion within nucleus, atom and molecule) is sustained to maintain identity of the system and prevent the collapse and disintegration of the system structure as such.

 Entropy is a thermal displacement (dynamic thermal volume) of thermal energy due to temperature as a thermal potential (dQ=TdS). It is an integral measure of (random) thermal energy redistribution (due to heat transfer and/or irreversible heat generation due to energy degradation) within a system mass and space, per absolute temperature level: dS=dQrev/T=CqdT/T with J/K unit. It may be expressed as being related to logarithm of number of all thermal, dynamic microstates (position and momenta), or to the sum of their logarithmic probability or uncertainty, that correspond, or are consistent with the given thermodynamic macrostate. Note that the meanings of "all relevant adjectives" are deeply important to reflect reality, and as such, "disorder" has metaphoric description for real systems. Entropy is increasing from perfectly-ordered (singular and unique) crystalline  structure at zero absolute temperature (zero reference) during reversible heating (entropy transfer) and entropy generation during irreversible energy conversion (lost of work-potential to thermal energy), i.e. energy degradation or random equi-partition within system material structure and space per absolute temperature level. NOTE that work-potential is preserved (conserved) if the non-equilibrium is preserved (with regard to the common equilibrium), i.e., during reversible processes. FURTHERMORE, entropy of a system for a given state is the same, regardless whether it is reached by reversible heat transfer or irreversible heat or irreversible work transfer. ... see also and The 2nd Law

Thermal Radiation refers to spontaneous electromagnetic radiation (photonic radiation) induced by random collision of elementary system structure (atoms and molecules), which is in turn due to kinetic energy of random motion of the system structure, i.e. system temperature. During random thermal interactions the electrons’ energy levels are changed within atoms, thus emitting photons, i.e. electromagnetic thermal radiation. It is also the final energy redistribution to the smallest (finest) structure known to man. Also, it is the price paid to maintain equilibrium state with the random thermal motion, and if not compensated from other sources outside of the system, the system will radiate away its thermal energy and cool towards absolute zero temperature.