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Mass–energy equivalence

2009-04-08T04:34:00.000-07:00

Mass–energy equivalence

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For other uses, see E=MC2 (disambiguation).

3-metre-tall sculpture of Einstein's 1905 E = mc² formula at the 2006 Walk of Ideas, Germany

In physics, mass–energy equivalence is the concept that mass and energy are not separate entities, but are interchangeable, with any mass having an associated energy, and any energy having an associated mass. (This is in addition to any other potential or kinetic energy the object may have.) This relationship is expressed using the formula

where

E₀ = the energy equivalent of the matter (technically its "rest energy")
m = mass
c = the speed of light in a vacuum (celeritas), (about 3×10⁸ m/s)

and total energy is then the sum of kinetic energy and rest energy.^[1] In other words, energy equals mass multiplied by the speed of light squared. Because the speed of light is a very large number, the formula implies that any small amount of matter, can in principle be converted to a very large amount of energy. This is the principle which allows nuclear energies to be calculated from mass measurements, but contrary to popular belief, it does nothing to explain the principle behind nuclear power, nuclear weapons, or natural processes in stars like the core of the sun. Nuclear reactions are properly explained by the nuclear force in the case of fusion, weak force in the case of beta decay and the Coulomb force between protons in the case of fission and alpha decay.

The discovery and formula were derived by Albert Einstein, who published it in 1905, in the paper "Does the inertia of a body depend upon its energy-content?", one of his Annus Mirabilis ("Miraculous Year") Papers.^[2] While Einstein was not the first to propose a mass–energy relationship, and various similar formulas appeared before Einstein's theory, Einstein was the first to propose that the equivalence of mass and energy is a general principle, a consequence of the symmetries of space and time.

In the formula, c² is the conversion factor required to convert from units of mass to units of energy. The formula does not depend on a specific system of units. In the International System of Units, the unit for energy is the joule, for mass the kilogram, and for speed meters per second. Note that 1 joule equals 1 kg·m²/s². In unit-specific terms, E (in joules) = m (in kilograms) multiplied by (299,792,458 m/s)².

[edit] Conservation of mass and energy

The above diagram illustrates five interrelated properties of mass together with the proportionality constants that relate these properties. Every sample of mass is believed to exhibit all five properties, however, due to extremely large proportionality constants, it is generally impossible to verify more than two or three properties for a specific sample of mass.

The Schwarzschild radius ( $r s$ ) represents the ability of mass to cause curvature in space and time.
The standard gravitational parameter ( $μ$ ) represents the ability of a massive body to exert Newtonian gravitational forces on other bodies.
Inertial mass ( $m$ ) represents the Newtonian response of mass to forces.
Rest energy ( $E 0$ ) represents the ability of mass to be converted into other forms of energy.
The Compton wavelength ( $λ$ ) represents the response of mass to local geometry.

The concept of mass–energy equivalence unites the concepts of conservation of mass and conservation of energy, allowing rest mass to be converted to forms of active energy (such as kinetic energy, heat, or light). Conversely, active energy in the form of kinetic energy or radiation can be converted to particles which have rest mass. The total amount of mass/energy in a closed system (as seen by a single observer) remains constant because energy cannot be created or destroyed and, in all of its forms, trapped energy exhibits mass. In relativity, mass and energy are two forms of the same thing, and neither one appears without the other.

[edit] Fast-moving objects and systems of objects

If a force is applied to an object in the direction of motion, the object gains momentum. It also gains energy because the force is doing work. But an object cannot be accelerated above the speed of light, regardless of how much energy it absorbs. Its momentum and energy continue to increase, but its speed approaches a constant value – the speed of light. This means that in relativity the momentum of an object cannot be a constant times the velocity, nor is the kinetic energy given by ½mv². (The latter is just a very good low-velocity approximation.)

The relativistic mass is defined as the ratio of the momentum of an object to its velocity, and it depends on the motion of the object relative to the observer. If the object is moving slowly, the relativistic mass is nearly equal to the rest mass and both can be considered equal to the usual Newtonian mass. If the object is moving quickly, the relativistic mass is greater than the rest mass. As the object approaches the speed of light, the relativistic mass tends towards infinity. When a force acts in the direction of motion, the relativistic mass goes up and the momentum goes up, but the speed hardly increases.

The relativistic mass is always equal to the total energy divided by c² shown as: m = E/c² The difference between the relativistic mass and the rest mass is the relativistic kinetic energy (divided by c²). Because the relativistic mass is exactly proportional to the energy, relativistic mass and relativistic energy are nearly synonyms; the only difference between them is the units. If length and time are measured in natural units, the speed of light is equal to 1, and even this difference disappears. Then mass and energy have the same units and are always equal, so it is redundant to speak about relativistic mass, because it is just another name for the energy.

For a bound or unbound system made up of many parts, such as an (nucleus, atom, planet, star), the relativistic mass is the sum of the relativistic masses of the parts, because the energies of the system parts add, as energy is conserved. However, it may be impossible to properly identify "parts" in such systems, because kinetic energies and fields also contribute to relativistic energies and masses. Thus, in an atomic nucleus, the nucleons on average have less mass than they do as free unbound particles, and it is presumed that this difference is due to lost mass of nuclear fields. However, the mass of individual nucleons in a nucleus cannot be measured directly.

In unbound systems made of many parts (example: any arbitrarily enclosed system, such as a cloud of expanding gas), the simple sumation nature of relativistic mass and relativistic energy is more clear. In such a system, the relativistic mass includes the kinetic energies of the gas molecules, and is a quantity which varies with the reference frame used to view the system. A cloud of gas moving with a net momentum will have more relativistic energy and relativistic mass than the same cloud viewed in the reference frame where it has no net momentum.

For this reason, in relativity people almost always reserve the useful short word "mass" to mean the rest mass. The rest mass of an object is the relativistic mass as measured when moving along with the object. By definition, rest mass is the same in all inertial frames. For a system of particles going off in different directions, the invariant mass is the analog of the rest mass, and it is defined as the total energy (divided by c²) in the center of mass frame. For a cloud of gas, the "rest mass" (or invariant mass) is the (total energy)/c^2, when viewed in the inertial frame where the gas has no net momentum (the center of momentum frame).

[edit] Meanings of the mass–energy equivalence formula

The mass–energy equivalence formula was displayed on Taipei 101 during the event of the World Year of Physics 2005.

Mass–energy equivalence says that a "body" (i.e. a mass) has a certain energy, even when it isn't moving. In Newtonian mechanics, a massive body at rest has no kinetic energy, and it may or may not have other (relatively small) amounts of internal stored energy such as chemical energy or thermal energy, in addition to any potential energy it may have from its position in a field of force. In Newtonian mechanics, none of these energies contributes to the mass.

In relativity, all the energy which moves along with a body adds up to the total energy of the body, which is proportional to the relativistic mass. Even a single photon traveling in empty space has a relativistic mass, which is its energy divided by c². If a box of ideal mirrors contains light, the mass of the box is increased by the energy of the light, since the total energy of the box is its mass.

Although a photon is never "at rest", it still has a rest mass, which is zero. This is by analogy with other particles, in which the square of the rest mass is found by subtracting the square of momentum from the square of the energy, in proper units. For photons, this quantity is always zero, and why photons are considered to be massless. If an observer chases a photon faster and faster, the observed energy (and thus also the relativistic mass) of the photon approaches zero as the observer approaches the speed of light, so that although photons have varying amounts of energy and relativistic mass, this may be made arbitrarily small for any photon by choice of observational inertial frame.

Systems of two or more photons moving in different directions (as for example from an electron–positron annihilation) cannot be made to have arbitrarily small energy by choice of observer or reference inertial frame; the reason is that the energy of one photon is decreased by chasing it, the energy of the other will be increased. Such systems thus have an inertial frame only in which their combined energy is minimized, but it does not become zero. In this frame, the momenta of the photons adds to zero, and their combined energy E gives them, as a system, an invariant mass given by m = E/c². This invariant mass is the same as that for the system which gave rise to the photons (for example the electron/positron system), when it is viewed from the inertial frame in which it has zero net momentum (called the center of momentum frame). The invariant mass of systems is thus a conserved property which is the same for all observers, and to which the energy of photons may contribute, even if individual photons are massless.

The formula m = E/c² also gives the amount of mass lost from a body when energy is removed from the system, since removal of system energy corresponds to removal of system mass. In a chemical or nuclear reaction, when heat and light are removed from the system, the mass of the system is decreased correspondingly. So the E in the formula is the energy released or removed, corresponding to a mass m which is lost. In those cases, the energy released and removed is equal in quantity to the mass lost, times c². Similarly, when energy of any kind is added to a resting body, or to a system of bodies, the increase in the mass as seen by a single observer (or as seen from any given inertial frame) is equal to the energy added, divided by c².

The rest mass of a system, however, is not necessarily the sum of the rest masses of its parts taken one-by-one, free from the system. This is a usual result from special relativity, in which all types of energy (including potential energy, kinetic energy, and the energy of massless photons) may add rest mass (or invariant mass) to a system. The difference between the rest mass of a bound system and the rest masses of the (free) parts before binding is the binding energy of the system, and represents energy which has been emitted in the formation of the system. However, this change results only because the system is open, and mass and energy are lost. If binding energy in a system is not allowed to escape the system, its mass does not change.

The invariant mass of a system is always the sum of the relativistic masses (and energies) of its parts, in the frame where the system as a whole can be seen as being "at rest" and the system momenta add to zero. Because the inertia (the relativistic mass) of a system (linked or free) is always the sum of all the inertias (all the relativistic masses) of its parts, the rest mass of an object can be seen as the particular value of its relativistic mass when the system as a whole is "at rest"; the best definition of this state being the inertial frame in which the system is seen to have minimal energy and no net momentum (the COM frame).

[edit] Consequences for nuclear physics

Max Planck pointed out that the mass–energy equivalence formula implied that bound systems would have a mass less than the sum of their constituents, once the binding energy had been allowed to escape. However, Planck was thinking about chemical reactions, where the binding energy is too small to measure. Einstein suggested that radioactive materials such as radium would provide a test of the theory, but even though a large amount of energy is released per atom, only a small fraction of the atoms decay.

Once the nucleus was discovered, experimenters realized that the very high binding energies of the atomic nuclei should allow calculation of their binding energies from mass differences. But it was not until the discovery of the neutron in 1932, and the measurement of its mass, that this calculation could actually be performed (see nuclear binding energy for example calculation). A little while later, the first transmutation reactions (such as ) verified Einstein's formula to an accuracy of +/- 0.5%.

The mass–energy equivalence formula was used in the development of the atomic bomb. By measuring the mass of different atomic nuclei and subtracting from that number the total mass of the protons and neutrons as they would weigh separately, one gets the exact binding energy available in an atomic nucleus. This is used to calculate the energy released in any nuclear reaction, as the difference in the total mass of the nuclei that enter and exit the reaction.

In quantum chromodynamics the modern theory of the nuclear force, most of the mass of the proton and the neutron is explained by special relativity. The mass of the proton is about twenty times greater than the sum of the rest masses of the quarks that make it up, while the gluons are massless. The extra energy of the quarks and gluons in a region with a proton, as compared to the energy of the quarks and gluons in the QCD vacuum, accounts for 95% of the mass.^[3]^[4]

[edit] Practical examples

Einstein used the CGS system of units (centimeters, grams, seconds, dynes, and ergs), but the formula is independent of the system of units. In natural units, the speed of light is defined to equal 1, and the formula expresses an identity: E = m. In the SI system (expressing the ratio E / m in joules per kilogram using the value of c in meters per second):

E / m = c² = (299,792,458 m/s)² = 89,875,517,873,681,764 J/kg (≈9.0 × 10¹⁶ joules per kilogram)

So one gram of mass — approximately the mass of a U.S. dollar bill — is equivalent to the following amounts of energy:

89.9 terajoules

24.9 million kilowatt-hours (≈25 GW·h)

21.5 billion kilocalories (≈21 Tcal)^[5]

21.5 kilotons of TNT-equivalent energy (≈21 kt)^[5]

85.2 billion BTUs^[5]

Any time energy is generated, the process can be evaluated from an E = mc² perspective. For instance, the "Gadget"-style bomb used in the Trinity test and the bombing of Nagasaki had an explosive yield equivalent to 21 kt of TNT. About 1 kg of the approximately 6.15 kg of plutonium in each of these bombs fissioned into lighter elements totaling almost exactly one gram less, after cooling [The heat, light, and electromagnetic radiation released in this explosion carried the missing one gram of mass.]^[6] This occurs because nuclear binding energy is released whenever elements with more than 62 nucleons fission.

Another example is hydroelectric generation. The electrical energy produced by Grand Coulee Dam’s turbines every 3.7 hours represents one gram of mass. This mass passes to the electrical devices which are powered by the generators (such as lights in cities), where it appears as a gram of heat and light.^[7] Turbine designers look at their equations in terms of pressure, torque, and RPM. However, Einstein’s equations show that all energy has mass, and thus the electrical energy produced by a dam's generators, and the heat and light which result from it, all retain their mass, which is equivalent to the energy. The potential energy – and equivalent mass – represented by the waters of the Columbia River as it descends to the Pacific Ocean would be converted to heat due to viscous friction and the turbulence of white water rapids and waterfalls were it not for the dam and its generators. This heat would remain as mass on site at the water, were it not for the equipment which converted some of this potential and kinetic energy into electrical energy, which can be moved from place to place (taking mass with it).

Whenever energy is added to a system, the system gains mass. A spring's mass increases whenever it is put into compression or tension. Its added mass arises from the added potential energy stored within it, which is bound in the stretched chemical (electron) bonds linking the atoms within the spring. Raising the temperature of an object (increasing its heat energy) increases its mass. If the temperature of the platinum/iridium "international prototype" of the kilogram — the world’s primary mass standard — is allowed to change by 1°C, its mass will change by 1.5 picograms (1 pg = 1 × 10^–12 g).^[8]
Note that no net mass or energy is really created or lost in any of these scenarios. Mass/energy simply moves from one place to another. These are some examples of the transfer of energy and mass in accordance with the principle of mass–energy conservation.

Note further that in accordance with Einstein’s Strong Equivalence Principle (SEP), all forms of mass and energy produce a gravitational field in the same way.^[9] So all radiated and transmitted energy retains its mass. Not only does the matter comprising Earth create gravity, but the gravitational field itself has mass, and that mass contributes to the field too. This effect is accounted for in ultra-precise laser ranging to the Moon as the Earth orbits the Sun when testing Einstein’s general theory of relativity.^[9]

According to E=mc², no closed system (any system treated and observed as a whole) ever loses mass, even when rest mass is converted to energy. This statement is more than an abstraction based on the principle of equivalence - it is a real-world effect.

All types of energy contribute to mass, including potential energies. In relativity, interaction potentials are always due to local fields, not to direct nonlocal interactions, because signals can't travel faster than light. The field energy is stored in field gradients or, in some cases (for massive fields), where the field has a nonzero value. The mass associated with the potential energy is the mass-energy of the field energy. The mass associated with field energy can be detected, in principle, by gravitational experiments, by checking how the field attracts other objects gravitationally. ^[10]

The energy in the gravitational field itself is different. There are several consistent ways to define the location of the energy in a gravitational field, all of which agree on the total energy when space is mostly flat and empty. But because the gravitational field can be made to vanish locally by choosing a free-falling frame, it is hard to avoid making the location dependent on the observer's frame of reference. The gravitational field energy is the familiar Newtonian gravitational potential energy in the Newtonian limit.

[edit] Efficiency

In nuclear reactions, typically only a small fraction of the total mass-energy is converted into heat, light, radiation and motion, into a form which can be used. When an atom fissions, it loses only about 0.1% of its mass, and in a bomb or reactor not all the atoms can fission. In a fission based atomic bomb, the efficiency is only 40%, so only 40% of the fissionable atoms actually fission, and only 0.04% of the total mass appears as energy in the end. In nuclear fusion, more of the mass is released as usable energy, roughly 0.3%. But in a fusion bomb (see nuclear weapon yield), the bomb mass is partly casing and non-reacting components, so that again only about 0.03% of the total mass is released as usable energy.

In theory, it should be possible to convert all the mass in matter into heat and light, but none of the theoretically known methods are practical. One way to convert all rest-mass into usable energy is to annihilate matter with antimatter. But antimatter is rare in our universe, and must be made first. Making the antimatter requires more energy than would be released.

Since most of the mass of ordinary objects is in protons and neutrons, in order to convert all the mass in ordinary matter to useful energy, the protons and neutrons must be converted to lighter particles. In the standard model of particle physics, the number of protons plus neutrons is nearly exactly conserved. Still, Gerardus 't Hooft showed that there is a process which will convert protons and neutrons to antielectrons and neutrinos^[11] . This is the weak SU(2) instanton proposed by Belavin Polyakov Schwarz and Tyupkin.^[12] This process, can in principle convert all the mass of matter into neutrinos and usable energy, but it is normally extraordinarily slow. Later it became clear that this process will happen at a fast rate at very high temperatures,^[13] since then instanton-like configurations will be copiously produced from thermal fluctuations. The temperature required is so high that it would only have been reached shortly after the big bang.

All conservative extensions of the standard model contain magnetic monopoles, and in the usual models of grand unification, these monopoles catalyze proton decay, a process known as the Callan-Rubakov effect.^[14] This process would be an efficient mass-energy conversion at ordinary temperatures, but it requires making monopoles and anti-monopoles first. The energy required to produce monopoles is believed to be enormous, but magnetic charge is conserved, so that the lightest monopole is stable. All these properties are deduced in theoretical models--- magnetic monopoles have never been observed, nor have they been produced in any experiment so far.

The third known method of total mass–energy conversion is using gravity, specifically black holes. Stephen Hawking showed^[15] that black holes radiate thermally with no regard to how they are formed. So it is theoretically possible to throw matter into a small black hole and use the emitted heat to generate power.

[edit] Background

E = mc² where m stands for rest mass (invariant mass) $m 0$ , applies most simply to single particles viewed in an inertial frame where they have no momentum. But it also applies to ordinary objects composed of many particles so long as the particles are moving in different directions so the "net" or total momentum is zero. The rest mass of the object includes contributions from heat and sound, chemical binding energies, and trapped radiation. Familiar examples are a tank of gas, or a hot poker. The kinetic energy of their particles, the heat motion and radiation, contribute to their weight on a scale according to E = mc².

The formula is the special case of the relativistic energy-momentum relationship:

This equation gives the rest mass of an object which has an arbitrary amount of momentum and energy. The interpretation of this equation is that the rest mass is the relativistic length of the energy-momentum four-vector.

If the equation $E = m c 2$ is used with the rest mass or invariant mass of the object, the $E$ given by the equation will be the rest energy of the object, and will change according to the object's internal energy, heat and sound and chemical binding energies (all of which must be added or subtracted from the object), but will not change with the object's overall motion (in the case of systems, the motion of its center of mass). However, if a system is closed, its invariant mass does not vary between different inertial observers (different inertial frames, and is also constant and conserved.

If the equation $E = m c 2$ is used with the relativistic mass of the object, the energy will be the total energy of the object, which is also conserved so long as no energy is added to or subtracted from the object, However, like the kinetic energy, this total energy will depend on the velocity of the object, and is different in different inertial frames. Thus, this quantity is not invariant between different inertial observers, even though it is constant over time for any single observer. As in the case of rest energy, these relationships for total energy are also true for systems of objects, so long as the system is closed.

Mass-Velocity Relationship

In developing special relativity, Einstein found that the kinetic energy of a moving body is

with $v$ the velocity, and $m 0$ the rest mass.

He included the second term on the right to make sure that for small velocities, the energy would be the same as in classical mechanics:

Without this second term, there would be an additional contribution in the energy when the particle is not moving.

Einstein found that the total momentum of a moving particle is:

and it is this quantity which is conserved in collisions. The ratio of the momentum to the velocity is the relativistic mass, m.

And the relativistic mass and the relativistic kinetic energy are related by the formula:

Einstein wanted to omit the unnatural second term on the right-hand side, whose only purpose is to make the energy at rest zero, and to declare that the particle has a total energy which obeys:

which is a sum of the rest energy $m 0 c 2$ and the kinetic energy. This total energy is mathematically more elegant, and fits better with the momentum in relativity. But to come to this conclusion, Einstein needed to think carefully about collisions. This expression for the energy implied that matter at rest has a huge amount of energy, and it is not clear whether this energy is physically real, or just a mathematical artifact with no physical meaning.

In a collision process where all the rest-masses are the same at the beginning as at the end, either expression for the energy is conserved. The two expressions only differ by a constant which is the same at the beginning and at the end of the collision. Still, by analyzing the situation where particles are thrown off a heavy central particle, it is easy to see that the inertia of the central particle is reduced by the total energy emitted. This allowed Einstein to conclude that the inertia of a heavy particle is increased or diminished according to the energy it absorbs or emits.

[edit] Relativistic mass

Main article: mass in special relativity

After Einstein first made his proposal, it became clear that the word mass can have two different meanings. The rest mass is what Einstein called m, but others defined the relativistic mass with an explicit index:

This mass is the ratio of momentum to velocity, and it is also the relativistic energy divided by c² (it is not Lorentz-invariant, in contrast to $m 0$ ). The equation E = m_relc² holds for moving objects. When the velocity is small, the relativistic mass and the rest mass are almost exactly the same.

E = mc² either means E = m₀c² for an object at rest, or E = m_relc² when the object is moving.

Also Einstein (following Hendrik Lorentz and Max Abraham) used velocity- and direction-dependent mass concepts (longitudinal and transverse mass) in his 1905 electrodynamics paper and in another paper in 1906.^[16] ^[17] However, in his first paper on E = mc² (1905) he treated m as what would now be called the rest mass.^[2] Some claim that (in later years) he did not like the idea of "relativistic mass."^[18] When modern physicists say "mass", they are usually talking about rest mass, since if they meant "relativistic mass", they would just say "energy".

[edit] Low-speed expansion

We can rewrite the expression for the energy as a Taylor series:

For speeds much smaller than the speed of light, higher-order terms in this expression get smaller and smaller because $v / c$ is small. For low speeds we can ignore all but the first two terms:

The total energy is a sum of the rest energy and the Newtonian kinetic energy.

The classical energy equation ignores both the $m 0 c 2$ part, and the high-speed corrections. This is appropriate, because all the high-order corrections are small. Since only changes in energy affect the behavior of objects, whether we include the $m 0 c 2$ part makes no difference, since it is constant. For the same reason, it is possible to subtract the rest energy from the total energy in relativity. By considering the emission of energy in different frames, Einstein could show that the rest energy has a real physical meaning.

The higher-order terms are extra correction to Newtonian mechanics which become important at higher speeds. The Newtonian equation is only a low-speed approximation, but an extraordinarily good one. All of the calculations used in putting astronauts on the moon, for example, could have been done using Newton's equations without any of the higher-order corrections.

[edit] History

While Einstein was the first to have correctly deduced the mass–energy equivalence formula, he was not the first to have related energy with mass. But nearly all previous authors thought that the energy which contributes to mass comes only from electromagnetic fields.^[19]^[20]^[21]^[22]

[edit] Newton: Matter and light

In 1717 Isaac Newton speculated that light particles and matter particles were inter-convertible in "Query 30" of the Opticks, where he asks:

“

Are not the gross bodies and light convertible into one another, and may not bodies receive much of their activity from the particles of light which enter their composition?

”

Since Newton did not understand light as the motion of a field, he was not speculating about the conversion of motion into matter. Since he did not know about energy, he could not have understood that converting light to matter is turning work into mass.

[edit] Electromagnetic rest mass

There were many attempts in the 19th and the beginning of the 20th century — like those of J. J. Thomson (1881), Oliver Heaviside (1888), and George Frederick Charles Searle (1896) — to understand how the mass of a charged object depends on the electrostatic field.^[19]^[20] Because the electromagnetic field carries part of the momentum of a moving charge, it was also suspected that the mass of an electron would vary with velocity near the speed of light. The formula of the mass-energy-relation given by them was $m = (4 / 3) E / c 2$ . ^[23]^[24]^[25]

Following Thomson and Searle (1896), Wilhelm Wien (1900), Max Abraham (1902), and Hendrik Lorentz (1904) argued that this relation applies to the complete mass of bodies, because any form of inertial mass was considered to be of electromagnetic origin.^[19] Wien went on by stating, that if it is assumed that gravitation is an electromagnetic effect too, than there has to be a strict proportionality between (electromagnetic) inertial mass and (electromagnetic) gravitational mass. To explain the stability of the matter-electron configuration, Poincaré in 1906 introduced some sort of pressure of non-electrical nature, which contributes the amount $- (1 / 3) E / c 2$ to the energy of the bodies. ^[26]^[27]^[28] ^[29]

[edit] Inertia of energy and radiation

James Clerk Maxwell (1874) and Adolfo Bartoli (1876) found out that the existence of tensions in the ether like the radiation pressure follows from the electromagnetic theory. However, Lorentz (1895) recognized that this led to a conflict between the action/reaction principle and Lorentz's ether theory. ^[30]^[31]^[32]

Poincaré

In 1900 Henri Poincaré studied this conflict and tried to determine whether the center of gravity still moves with a uniform velocity when electromagnetic fields are included.^[22] He noticed that the action/reaction principle does not hold for matter alone, but that the electromagnetic field has its own momentum. The electromagnetic field energy behaves like a fictitious fluid ("fluide fictif") with a mass density of $E / c 2$ (in other words m = E/c²). If the center of mass frame is defined by both the mass of matter and the mass of the fictitious fluid, and if the fictitious fluid is indestructible - it is neither created or destroyed - then the motion of the center of mass frame remains uniform. But electromagnetic energy can be converted into other forms of energy. So Poincaré assumed that there exists a non-electric energy fluid at each point of space, into which electromagnetic energy can be transformed and which also carries a mass proportional to the energy. In this way, the motion of the center of mass remains uniform. Poincaré said that one should not be too surprised by these assumptions, since they are only mathematical fictions.^[33]

But Poincaré's resolution led to a paradox when changing frames: if a Hertzian oscillator radiates in a certain direction, it will suffer a recoil from the inertia of the fictitious fluid. In the framework of Lorentz ether theory Poincaré performed a Lorentz boost to the frame of the moving source. He noted that energy conservation holds in both frames, but that the law of conservation of momentum is violated. This would allow a perpetuum mobile, a notion which he abhorred. The laws of nature would have to be different in the frames of reference, and the relativity principle would not hold. Poincaré's paradox was resolved^[22] by Einstein's insight that a body losing energy as radiation or heat was losing a mass of the amount $m = E / c 2$ . The Hertzian oscillator loses mass in the emission process, and momentum is conserved in any frame. Einstein noted in 1906 that Poincaré's solution to the center of mass problem and his own were mathematically equivalent (see below).

Poincaré came back to this topic in "Science and Hypothesis" (1902) and "The Value of Science" (1905). This time he rejected the possibility that energy carries mass: "... [the recoil] is contrary to the principle of Newton since our projectile here has no mass, it is not matter, it is energy". He also discussed two other unexplained effects: (1) non-conservation of mass implied by Lorentz's variable mass $γ m$ , Abraham's theory of variable mass and Kaufmann's experiments on the mass of fast moving electrons and (2) the non-conservation of energy in the radium experiments of Madame Curie.

Abraham and Hasenöhrl

Following Poincaré, Max Abraham in 1902 introduced the term "electromagnetic momentum" to maintain the action/reaction principle.^[21] Poincaré's result was verified by him, whereby the field density of momentum per cm³ is $E / c 2$ and $E / c$ per cm².^[34]

In 1904, Friedrich Hasenöhrl specifically associated inertia with radiation in a paper, which was according to his own words very similar to some papers of Abraham.^[21] Hasenöhrl suggested that part of the mass of a body (which he called apparent mass) can be thought of as radiation bouncing around a cavity. The apparent mass of radiation depends on the temperature (because every heated body emits radiation) and is proportional to its energy, and he first concluded that $m = (8 / 3) E / c 2$ . However, in 1905 Hasenöhrl published a summary of a letter, which was written by Abraham to him. Abraham concluded that Hasenöhrl's formula of the apparent mass of radiation is not correct, and based on his definition of electromagnetic momentum and longitudinal electromagnetic mass Abraham changed it to $m = (4 / 3) E / c 2$ , the same value for the electromagnetic mass for a body at rest. Hasenöhrl re-calculated his own derivation and verified Abraham's result. He also noticed the similarity between the apparent mass and the electromagnetic mass. However, Hasenöhrl stated that this energy-apparent-mass relation only holds as long a body radiates, i.e. if the temperature of a body is greater than 0 K.^[35]^[36]

However, Hasenöhrl did not include the pressure of the radiation on the cavity shell. If he had included the shell pressure and inertia as it would be included in the theory of relativity, the factor would have been equal to 1 or $m = E / c 2$ . This calculation assumes that the shell properties are consistent with relativity, otherwise the mechanical properties of the shell including the mass and tension would not have the same transformation laws as those for the radiation.^[37] Nobel Prize-winner and Hitler advisor Philipp Lenard claimed that the mass–energy equivalence formula needed to be credited to Hasenöhrl to make it an Aryan creation.^[38]

[edit] Einstein: Mass–energy equivalence

Albert Einstein did not formulate exactly the formula $E = m c 2$ in his 1905 paper "Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?" ("Does the Inertia of a Body Depend Upon Its Energy Content?", published in Annalen der Physik on 27 September), one of the articles now known as his Annus Mirabilis Papers.^[2]

That paper says: If a body gives off the energy L in the form of radiation, its mass diminishes by $L / c 2$ . Here, "radiation" means electromagnetic radiation, or light, and mass means the ordinary Newtonian mass of a slow moving object.

In Einstein's first formulation, it is the difference in the mass '' before and after the ejection of energy that is equal to $L / c 2$ , not the entire mass '' of the object. Objects with zero mass presumably have zero energy, so the extension that all mass is proportional to energy is obvious from this result. In 1905, even the hypothesis that changes in energy are accompanied by changes in mass was untested. Not until the discovery of the first type of antimatter (the positron in 1932) was it found that all of the mass of pairs of resting particles could be converted to radiation.

1905 – First correct derivation

Einstein considered a body at rest with mass M. If the body is examined in a frame moving with nonrelativistic velocity v, it is no longer at rest and in the moving frame it has momentum Mv.

Einstein supposed the body emits two pulses of light to the left and to the right, each carrying an equal amount of energy E/2. Since the two pulses are equal, the object remains at rest after the emission since the two beams are equal in strength and carry opposite momentum.

But if the same process is considered in a frame moving with velocity v to the left, the pulse moving to the left will be redshifted while the pulse moving to the right will be blue shifted. The blue light carries more momentum than the red light, so that the momentum of the light in the moving frame is not balanced. The light is carrying some net momentum to the right.

The object hasn't changed its velocity before or after the emission. Yet in this frame it has lost some right-momentum to the light. The only way it could have lost momentum is by losing mass. This also solves Poincaré's radiation paradox, discussed above.

The velocity is small, so the right moving light is blueshifted by an amount equal to the nonrelativistic Doppler shift factor (1 - v/c). The momentum of the light is its energy divided by c, and it is increased by a factor of v/c. So the right moving light is carrying an extra momentum $Δ P$ given by:

The left-moving light carries a little less momentum, by the same amount $Δ P$ . So the total right-momentum in the light is twice $Δ P$ . This is the right-momentum that the object lost.

The momentum of the object in the moving frame after the emission is reduced by this amount:

So the change in the object's mass is equal to the total energy lost divided by $c 2$ . Since any emission of energy can be carried out by a two step process, where first the energy is emitted as light and then the light is converted to some other form of energy, any emission of energy is accompanied by a loss of mass. Similarly, by considering absorption, a gain in energy is accompanied by a gain in mass. Einstein concludes that all the mass of a body is a measure of its energy content.

1906 – Relativistic center-of-mass theorem

Like Poincaré, Einstein concluded in 1906 that the inertia of electromagnetic energy is a necessary condition for the center-of-mass theorem to hold. On this occasion, Einstein referred to Poincaré's 1900 paper and wrote:^[39]

“

Although the merely formal considerations, which we will need for the proof, are already mostly contained in a work by H. Poincaré², for the sake of clarity I will not rely on that work.^[40]

”

In Einstein's more physical, as opposed to formal or mathematical, point of view, there was no need for fictitious masses. He could avoid the perpetuum mobile problem, because based on the mass–energy equivalence he could show that the transport of inertia which accompanies the emission and absorption of radiation solves the problem. Poincaré's rejection of the principle of action-reaction can be avoided through Einstein's $E = m c 2$ , because mass conservation appears as a special case of the energy conservation law.

[edit] Others

During the nineteenth century there were several speculative attempts to show that mass and energy were proportional in various discredited ether theories.^[41] In particular, the writings of Samuel Tolver Preston,^[42]^[43] and a 1903 paper by Olinto De Pretto,^[44]^[37] presented a mass–energy relation. De Pretto's paper received recent press coverage when Umberto Bartocci discovered that there were only three degrees of separation linking De Pretto to Einstein, leading Bartocci to conclude that Einstein was probably aware of De Pretto's work.^[45]^[46]

Preston and De Pretto, following Le Sage, imagined that the universe was filled with an ether of tiny particles which are always moving at speed c. Each of these particles have a kinetic energy of mc² up to a small numerical factor. The nonrelativistic kinetic energy formula did not always include the traditional factor of 1/2, since Leibniz introduced kinetic energy without it, and the 1/2 is largely conventional in prerelativistic physics.^[47] By assuming that every particle has a mass which is the sum of the masses of the ether particles, the authors would conclude that all matter contains an amount of kinetic energy either given by E = mc² or 2E = mc² depending on the convention. A particle ether was usually considered unacceptably speculative science at the time,^[48] and since these authors didn't formulate relativity, their reasoning is completely different from that of Einstein, who used relativity to change frames.

Independently, Gustave Le Bon in 1905 speculated that atoms could release large amounts of latent energy, reasoning from an all-encompassing qualitative philosophy of physics.^[49]^[50]

[edit] Radioactivity and nuclear energy

It was quickly noted after the discovery of radioactivity in 1897, that the total energy due to radioactive processes is about one million times greater than that involved in any known molecular change. However, it raised the question where this energy is coming from. After eliminating the idea of absorption and emission of some sort of Lesagian ether particles, the existence of a huge amount of latent energy, stored within matter, was proposed by Ernest Rutherford and Frederick Soddy in 1903. Rutherford also suggested that this internal energy is stored within normal matter as well. He went on to speculate in 1904:^[51]^[52]

“

If it were ever found possible to control at will the rate of disintegration of the radio-elements, an enormous amount of energy could be obtained from a small quantity of matter.

”

Einstein mentions in his 1905 paper that mass-energy equivalence might perhaps be tested with radioactive decay, which releases enough energy (the quantitative amount known roughly even by 1905) to possibly be "weighed," when missing. But the idea that great amounts of usable energy could be liberated from matter, however, proved initially difficult to substantiate in a practical fashion. Because it had been used as the basis of much speculation, Rutherford himself, rejecting his ideas of 1904, was once reported in the 1930s to have said that: "Anyone who expects a source of power from the transformation of the atom is talking moonshine."

The popular connection between Einstein, E=mc², and the atomic bomb was prominently indicated on the cover of Time magazine in July 1946 by the writing of the equation on the mushroom cloud itself.

This changed dramatically after the demonstration of energy released from nuclear fission after the atomic bombings of Hiroshima and Nagasaki in 1945. The equation E = mc² became directly linked in the public eye with the power and peril of nuclear weapons. The equation was featured as early as page 2 of the Smyth Report, the official 1945 release by the US government on the development of the atomic bomb, and by 1946 the equation was close-enough linked with Einstein's work that the cover of Time magazine prominently featured a picture of Einstein next to an image of a mushroom cloud emblazoned with the equation.^[53] Einstein himself had only a minor role in the Manhattan Project: he had cosigned a letter to the US President in 1939 urging funding for research into atomic energy, warning that an atomic bomb was theoretically possible. The letter persuaded Roosevelt to devote a significant portion of the wartime budget to atomic research. Without a security clearance, Einstein's only scientific contribution was an analysis of an isotope separation method based on the rate of molecular diffusion through pores, a now-obsolete process that was then competitive and contributed a fraction of the enriched uranium used in the project.^[54]

While E = mc² is useful for understanding the amount of energy released in a fission reaction, it was not strictly necessary to develop the weapon. As the physicist and Manhattan Project participant Robert Serber put it: "Somehow the popular notion took hold long ago that Einstein's theory of relativity, in particular his famous equation E = mc², plays some essential role in the theory of fission. Albert Einstein had a part in alerting the United States government to the possibility of building an atomic bomb, but his theory of relativity is not required in discussing fission. The theory of fission is what physicists call a non-relativistic theory, meaning that relativistic effects are too small to affect the dynamics of the fission process significantly."^[55] However the association between E = mc² and nuclear energy has since stuck, and because of this association, and its simple expression of the ideas of Albert Einstein himself, it has become "the world's most famous equation".^[56]

While Serber's view of the strict lack of need to use mass-energy equivalence in designing the atomic bomb is correct, it does not take into account the pivotal role which this relationship played in making the fundamental leap to the initial hypothesis that large atoms could split into approximately equal halves. In late 1938, while on the winter walk on which they solved the meaning of Hahn's experimental results and introduced the idea that would be called atomic fission, Lise Meitner and Otto Robert Frisch made direct use of Einstein's equation to help them understand the quantitative energetics of the reaction which overcame the "surface tension-like" forces holding the nucleus together, and allowed the fission fragments to separate to a configuration from which their charges could force them into an energetic "fission." To do this, they made use of "packing fraction," or nuclear binding energy values for elements, which Mitner had memorized. These, together with use of E = mc² allowed them to realize on the spot that the basic fission process was energetically possible:

...We walked up and down in the snow, I on skis and she on foot. ...and gradually the idea took shape... explained by Bohr's idea that the nucleus is like a liquid drop; such a drop might elongate and divide itself... We knew there were strong forces that would resist, ..just as surface tension. But nuclei differed from ordinary drops. At this point we both sat down on a tree trunk and started to calculate on scraps of paper. ...the Uranium nucleus might indeed be an unstable drop, ready to divide itself... But, ...when the two drops separated they would be driven apart by electrical repulsion, about 200 MeV in all. Fortunately Lise Meitner remembered how to compute the masses of nuclei... and worked out that the two nuclei formed... would be lighter by about one-fifth the mass of a proton. Now whenever mass disappears energy is created, according to Einstein's formula E = mc2, and... the mass was just equivalent to 200 MeV; it all fitted! ^[57]

TERMODINAMIKA

2009-04-08T04:26:00.000-07:00

Parameter termodinamika untuk perubahan keadaan diperlukan untuk mendeskripsikan ikatan kimia, sruktur dan reaksi. Hal ini juga berlaku dalam kimia anorganik, dan konsep paling penting dalam termodinamika dipaparkan di bagian ini.

Pengetahuan termodinamika sederhana sangat bermanfaat untuk memutuskan apakah struktur suatu senyawa akan stabil, kemungkinan kespontanan reaksi, perhitungan kalor reaksi, penentuan mekanisme reaksi dan pemahaman elektrokimia.

Entalpi adalah kandungan kalor sistem dalam tekanan tetap, perubahan(∆H) bernilai negatif untuk reaksi eksoterm, dan positif untuk reaksi endoterm. Entalpi reaksi standar(∆H0) adalah perubahan entalpi dari 1 mol reaktan dan produk pada keadaan standar (105 Pa dan 298.15 K).

Entalpi pembentukan standar(∆Hf0) suatu senyawa adalah entalpi reaksi standar untuk pembentukan senyawa dari unsur-unsurnya. Karena entalpi adalah fungsi keadaan, entalpi reaksi standar dihitung dengan mendefinisikan entalpi pembentukan zat sederhana (unsur) bernilai nol.

Entropi adalah fungsi keadaan, dan merupakan kriteria yang menentukan apakah suatu keadaan dapat dicapai dengan spontan dari keadaan lain. Hukum ke-2 termodinamika menyatakan bahwa entropi, S, sistem yang terisolasi dalam proses spontan meningkat. Dinyatakan secara matemati:

∆S > 0

Proses yang secara termodinamika ireversibel akan menghasilkan entropi. Entropi berkaitan dengan ketidakteraturan sistem dalam termodinamika statistik, menurut persamaan:

S = klnW .

k adalah tetapan Boltzmann, dan W adalah jumlah susunan atom atau molekul dalam sistem dengan energi yang sama, dan berhubungan dengan besarnya ketidakteraturan. Dengan meningkatnya entropi, meningkat pula ketidakteraturan sistem.

Energi bebas Gibbs Kuantitas ini didefinisikan dengan:

∆G = ∆H - T∆S

reaksi spontan terjadi bila energi Gibbs reaksi pada suhu dan tekanan tetap negatif. Perubahan energi bebas Gibbs standar berhubungan dengan tetapan kesetimbangan reaksi A = B melalui:

∆ G0 = -RT ln K.

K bernilai lebih besar dari 1 bila ∆G0 negatif, dan reaksi berlangsung spontan ke kanan.

is my life

2009-03-23T03:51:00.000-07:00

sejarah dan asal usul Gitar

Sebelum kita tahu dan bisa bermain gitar tidak ada salahnya kita mengerti dulu tentang sejarah alat musik gitar ini, karena dengan kita mengenalnya bukankah kita lebih bisa mencintainya ?? inilah secuil tentang sejarah gitar
Dari Babilonia hingga Senar Enam
Sejarah gitar dipercaya dimulai di wilayah Timur Dekat. Di antara puing-puing yang di temukan di Babilonia, yang paling relevan adalah gitar yang dibuat pada 1900-1800 SM. Dari masa itu, hingga tahun 1650, gitar mengalami evolusi yang begitu rumit dan beraneka ragam. Begitu banyak jenis dan masing-masing memiliki nama yang berbeda.
Beberapa kalangan berpendapat lain, menganggap gitar justru berasal dari negara Spanyol karena alat musik gitar mirip sama alat musik Spanyol yang bernama Vihuela yang beredar pada awal abad ke-16. Alat baru ini (gitar) mempunyai cara pembuatan yang sama dengan alat musik ukulele. Gitar pertama kali yang dibuat sebenarnya berukuran sangat kecil dan juga hanya memiliki empat dawai, seperti ukulele.
Pada masa klasik banyak terdapat publikasi yang dilakukan oleh para pembuat lagu dan juga para pemusik. Seperti Fernando Sor, Mauro Guiliani, Matteo Carcassi, Fernando Caulli, dan masih banyak para pencipta yang mengembangakan metode bermain gitar yang akhirnya menjadi permainan yang umum dan dapat diterima.
Instrumen yang penting kontribusinya dalam perkembangan gitar adalah instrumen Cittern. Instrumen ini juga berbentuk menyerupai buah pir dengan bagian belakang yang rata, dengan empat atau lima pasang senar dari kawat dan dengan fretting yang permanen apakah itu diatonik seperti Appalachian Dulcimer ataupun chromatic seperti gitar modern. Tuning head sudah dipasang mirip seperti pada gitar atau mandolin. Stemannya sama dengan mandolin (in fifths) dengan fingering dan chord yang sama dan dimainkan dengan plectrum atau pick.
Four Course Guitar memiliki 4 pasang senar, body berbentuk gitar dan soundboard yang rata, bridge dari lute dan bagian belakang dibuat setengah melengkung tetapi tidak terlalu membentuk bulatan. Instrumen ini berukuran seperti gitar anak-anak.
Five Course Guitar muncul sekitar tahun 1490 dan mirip dengan four course guitar dengan tambahan satu pasang senar bass. Instrumen ini dinamakan juga English Guitar.
Ada pula Vihuela De Mano berasal dari Spanyol dan merupakan instrumen dengan enam pasang senar. Bodynya cukup besar seperti gitar klasik jaman sekarang dan mempunyai beberapa lubang suara di atasnya. Instrumen ini menggunakan fixed bridge dan kemungkinan merupakan nenek moyang langsung dari gitar 12 senar USA yang masuk ke Amerika Utara melalui Mexico, Texas dan Louisiana.
Masih banyak jenis gitar lainnya yang terus berkembang. Gitar seperti yang kita kenal sekarang, yaitu bersenam enam, baru muncul sekitar tahun 1750. Dan selama sekitar 90 tahun berikutnya (hingga tahun 1840), gitar senar enam ini cukup pesat berkembang di Spanyol.
Masuknya Gitar di Indonesia
Penjajahan, selain menyisakan catatan kepedihan, juga seni. Salah satunya adalah dibawanya gitar oleh orang-orang Purtugis di sekitar abad ke-17.
Pada waktu itu sejumlah tawanan asal Portugis di Malaka dimukimkan oleh Belanda di kawasan berawa-rawa di Jakarta Utara, di sebuah kampung Tugu. Agar mereka tidak bosan, mereka menghibur diri dengan bermain musik. Nah, musik yang mereka gunakan saat itu adalah gitar. Konon, dari hasil pengenalan rakyat terhadap alat musik itu, lahirlah beberapa alat musik petik yang dimainkan untuk mengiringi lagu-lagu keroncong.
Ada 3 jenis gitar yang dimainkan para tawanan saat itu, yaitu :
1.Gitar Monica, yang terdiri dari 3 dawai
2.Gitar Rorenga, yang terdiri dari 4 dawai
3.Gitar Jitera, yang terdiri dari 5 dawai.
Dua abad kemudian gitar dan keroncong menjadi populer di kalangan bangsawan dan kemudian menyebar ke pelosok tanah air.
Gitar Elektrik
Di zaman modern, orang mulai mengenal gitar yang memanfaatkan sumber daya listrik. Bunyi yang dihasilkanya berbeda dengan bunyi gitar klasik.Gitar listrik pertama kali dibuat pada 1932 oleh Adolphus Rickenbacker. Gitar ini mengambil bentuk rancangan gitar Spanyol tradisional.
Setelah itu, perkembangannya terus berlanjut. Ide yang mempercepat perkembangannya diawali dari sering diadakannya konser-konser dengan jumlah penonton yang banyak; sehingga jikalau tanpa bantuan sound system, suaranya tak terdengar, apalagi bila penonton berteriak-teriak riuh.
Produsen gitar bermunculan di mana-mana. Dua yang terkenal adalah Fender dan Ibanez. Selain itu, media-media juga mempublikasikan pemain-pemain gitar hebat melalui mejalah bergengsi seperti Guitar Player. Kini, komponen-komponen pada gitar listrik, seperti bridge/tremolo, pick-up, juga senar, bahkan diproduksi terpisah dari produser gitar.
Ada pula hal-hal yang nyentrik dalam perkembangan gitar seperti gitar bersenar tujuh yang dipopulerkan oleh Steve Vai di tahun 1989. Ide ini datang saat ia bergabung dengan David Lee Roth Band pada tahun 1985, menggarap album Crazy from the Heat. Ia memutuskan demikian karena sang bassis, Billy Sheehan, sering menyetel bassnya dengan formasi lain bernama Drop D Tuning (dari atas ke bawah: D-A-D-G, umumnya E-A-D-G). Bekerjasama dengan Ibanez tahun 1987, akhirnya lahirlah gitar pertama bersenar tujuh, dengan dawai teratas, alias ketujuh, bernada B. Gitar ini dinamakan The Universe-7 String. Vai juga memiliki gitar dengan neck yang berlawanan (menghadap ke kiri dan kanan), untuk membuktikan kemampuannya bermain kidal.
Sementara itu, Eddie van Halen, menjadi pelopor dalam penggunaan whammy bar up-down yang kemudian dikenal sebagai Floyd Rose tremolo/bridge. Inovasi ini lengkap dengan pengunci senar pada bagian nut gitar. Sistem ini dikenal sebagai locking nut tremolo system.
Eddie mengembangkan sistem tremolo yang sudah ada sebelumnya. Yaitu tremolo yang hanya bisa ditekan down atau turun (menghasilkan nada yang lebih rendah). Sistem lama ini dikembangkan oleh pabrik Fender dan terpasang sebagai perlengkapan standar pada model Stratocaster. Inovasi ini terpikir olehnya pada sekitar tahun 1976. Saat itu para gitaris hebat seperti Ritchie Blackmore dan Jimmy Page sering mengalami masalah pada tuning gitar mereka. Karena mereka sering mem-bending senar terlalu banyak untuk menghasilkan suara yang 1½ nada lebih tinggi. Akibatnya senar jadi kendor dan tentunya nadanya juga jadi fals. Dengan locking nut tremolo system, senar dikunci di bagian nut gitar agar tidak bergeser ketegangannya.
Sedikit tambahan, pada tahun 1991 juga pernah dibuat gitar yang paling besar di Amerika Serikat, tepatnya di Indiana. Bayangkan, panjangnya sampai11 meter, hampir sama panjang dengan dua buah mobil limosin! Gitar ini membutuhkan 6 orang untuk memainkannya.

my life my adventure

Mass–energy equivalence

Mass–energy equivalence

From Wikipedia, the free encyclopedia

Contents

[edit] Conservation of mass and energy

[edit] Fast-moving objects and systems of objects

[edit] Meanings of the mass–energy equivalence formula

[edit] Consequences for nuclear physics

[edit] Practical examples

[edit] Efficiency

[edit] Background

[edit] Relativistic mass

[edit] Low-speed expansion

[edit] History

[edit] Newton: Matter and light

[edit] Electromagnetic rest mass

[edit] Inertia of energy and radiation

[edit] Einstein: Mass–energy equivalence

[edit] Others

[edit] Radioactivity and nuclear energy

TERMODINAMIKA

is my life