Questions tagged [mass-energy]

The special-relativistic relation connecting energy with mass, $ E^2 - (m c^2)^2= (pc)^2 $. May be used to provide accounting constraints in energy and momentum, both conserved in total, even in reactions where $m$ is not.

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How can Electricity travel at the speed of light?

If electricity is the flow of electrons, how come it can flow at the speed of light? Shouldn't how fast it moves be limited to a speed lower than the speed of light because it has mass?
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Binding energy in lorentz boost

In the first lecture here- M theory and string theory lecture 1, Leonard Susskind The lecturer gives a heuristic as to why a string of length $L$ has mass $L$. Set all $h=c=1$. His explanation is that ...
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Nuclear binding energy and gravitation

A nucleus $A$ can be split into two smaller nuclei $B$ and $C$. It is well known that the sum of the masses of $B$ and $C$ will not equal the mass of $A$ due to the nuclear binding energy and the ...
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What is the pure Energy in the term of no-matter and no-anti-matter? [duplicate]

what is the pure Energy in the term of no-matter and no-anti-matter? Explain why is the energy explore in term of visibility and heat?
warrior madness's user avatar
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Where does the $\pm$ in Einstein's energy-mass equivalence come from?

Our professor taught us the equation $E= mc^2$ today, but he mentioned that this is only a part of a solution. He never taught us where it came from, but he did mention that this is only a partial ...
CarnotEngine's user avatar
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Energy gained by a black hole [duplicate]

Consider a massive particle falling into a black hole with a very high kinetic energy, for instance, an a particle with travelling at 99.9999999999% of the speed of light towards it. The mass-energy ...
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Confusion about energy conservation for fusion and fission (binding energy and $Q$-value)

In a nuclear reaction, a system consisting of a nucleus or nuclei lose mass, and this mass gets turned into energy, which is quantified by $E=mc^{2}$. But I'm conceptually confused. According to ...
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Can we see the rest-energy of a mass as its kinetic energy in the $ct$-direction?

A mass $m$ at rest has an energy $E=mc^2$. Can we say this is its kinetic energy in the $ct$-direction?
Il Guercio's user avatar
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How is the energy content in 1 kg of water and petrol the same?

We know petrol is a fuel and water is not. But how come 1 kg of water and 1 kg of petrol have the same energy content? The total energy is given by $E=mc^2$, it says nothing about the chemical ...
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What is the combined mass of two relativistic particles inelastically colliding into a singular relativistic particle?

A perfectly inelastic central collision of two equal relativistic particles whose kinetic energies are equal to their resting energies results a single relativistic particle (and nothing but it). The ...
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How to do the non-relativistic limit of an Energy expression?

I solved for the bound state energies of a system using the Dirac equation, I was told that to compare my result to the energies obtained with the Schrodinger equation I need to do the non-...
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Can "mass" be eliminated as a concept by always thinking of it as energy? [closed]

In the Newtonian sense, "mass" is representative of a body's general resistance to motion. Einstein derived $E = mc^2$ but it was in the context of the amount of mass lost after a body emits ...
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Why do my Milwaukee batteries weigh different amounts when charged vs uncharged

We use m12 small sized Milwaukee battery’s and I noticed when I use them I feel like they weigh different when using them sometimes while using them and then I read a article about batteries loosing ...
Kelton Clay's user avatar
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3 answers
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Please explain $E = γmc^2$ more intuitively [closed]

My name is Shaun and I am 14 years old. Lately I have been trying to learn about $E = mc^2$, and I came across Fermilabs video about $E = γmc^2$, where $γ$ is the Lorentz factor. My question is how ...
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Law of conservation of Momentum example

Consider if I was standing on a boat with no external forces acting on us. Considering I move around on the boat on account of law of conservation of momentum the boat would gain some velocity to ...
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Where would the extra mass due to mass-energy equivalence for a system of two charged particles come from? How could that statement make any sense?

Suppose we have two point charges of rest masses $m_{1}, m_{2}$ and charges $q_{1}, q_{2}$. The electrostatic potential energy of the two objects is $U = k\cdot q_{1}q_{2}/r$ where $r$ is the distance ...
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Why does the mass deficit exists? [duplicate]

Everyone knows Albert Einstein's famous formula: $E = m * c^2$ In nuclear fission, we make use of it by converting mass into energy. But what is the mass that gets converted? Of course, when nuclei ...
dark_ursus's user avatar
1 vote
3 answers
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Why does mass make curvature in spacetime? [duplicate]

According to Einstein's general relativity theory, matter with mass makes curvature in spacetime. The greater the mass, the curvature in spacetime will be greater. My questions: Why will mass make ...
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Equivalent mass enhanced inside dielectric (modified Rohrlich)?

I shall modify an argument for energy-mass equivalence due to Fritz Rohrlich to be valid inside a dielectric medium with refractive index $n$ and light velocity $c_n=c/n$. (Alternative argument to the ...
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Why does Schwarzschild radius increase linearly with mass?

Suppose there are $2$ black holes with masses $M_{earth}$ and $M_{sun}$, shouldn't the $M_{sun}$ crush the matter within it more intensely compared to $M_{earth}$? Based on this, shouldn't the ...
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Equivalent mass enhanced inside dielectric medium?

Imagine a box of mass $M$ and length $L$ containing a medium with refractive index $n$. A photon is emitted from the left-hand side of the box and is absorbed on the right-hand side. Let us assume ...
John Eastmond's user avatar
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Binding energy vs Mass number Plot and Pairing effect for higher nuclei region

I have two doubts. In every text or literature, one always see the graph of binding energy per nucleon vs mass number and not binding energy vs mass number. Is it like we don't interpret any useful ...
Anshul Sharma's user avatar
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How Should the True Energy Gain of the NIF's "Scientific Breakeven" Fusion Experiment be Calculated?

According to this article "LLNL’s experiment surpassed the fusion threshold by delivering 2.05 megajoules (MJ) of energy to the target, resulting in 3.15 MJ of fusion energy output." It isn'...
phil1008's user avatar
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How can negative potential energy cause mass decrease?

The mass of a hydrogen is less than its constituent parts(proton/electron). The explanation given for this is the following: Youtube For hydrogen, $m = m_{components} + m_{extra}$ where we can write $...
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Energy with mass correlation

If the watch is working/ticking, its moving parts (gear, hand) contributes to extra mass where if we add potential, kinetic, and thermal energy and divide it by $c^2$, we get extra mass (small, but ...
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How can charge be conserved when mass isn't? [duplicate]

If mass (consisting of protons and electrons) can be converted to energy by running it at the speed of light, wouldn't that also convert charge as charge is due to and quantized over electrons? For ...
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The logic behind Einstein's derivation of $E=mc^2$

There is a Physics.SE question asking for a proof of $$E=mc^2$$ Multiple users on this forum responded with an argument that is summarized by the user Abhimanyu Pallavi Sudhir as follows: quote: &...
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What happen with missing energy conserved as mass in decay $\rm {}^4H\to {}^3H + n$?

What happen with missing energy conserved as mass in decay $\rm {}^4H\to {}^3H + n$? https://en.wikipedia.org/wiki/Isotopes_of_hydrogen $${}^4H \leftrightarrow {}^3H + n$$ $$4.02643 > 3....
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Contradiction b/w Big bang theory and conservation of mass

As per the conservation of mass, matter cannot be created or destroyed. Doesn't this contradict the big bang theory? Like, it states that it all started from a single point. But seeing the massive ...
Atharva Patankar's user avatar
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Confusion in energy-mass equivalence: Why would gravitational effects remain the same even when you move at high speeds?

It is said that most of what we call "mass" of nucleons are in fact from the kinetic and binding energies of quarks, and that the rest mass of quarks, from the higgs mechanism is much ...
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Mass density of photons in a refractive medium

The effective mass density of photons in a vacuum $\rho^{vac}_M$ is related to the photon energy density $\rho^{vac}_E$ by $$\rho^{vac}_M=\frac{\rho^{vac}_E}{c^2}.$$ Is it true that the mass density ...
John Eastmond's user avatar
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1 answer
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Could the energy emitted by galaxies contribute to the dark matter phenomenon?

I'm pondering a concept regarding the energy-mass conversion in the context of cosmology, specifically related to the light emitted by galaxies over billions of years. Einstein's famous equation E=mc^...
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3 answers
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A question regarding Open, Closed and Isolated systems

While revising Chemical Thermodynamics as usual, I came across a term called Closed System - which is defined as a system which exchanges energy with the surroundings and not matter. But, according ...
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Why we can take for granted that energy binding is associated with inertial mass?

It is common to state that a proton is bounded state of three quarks, and that the QCD energy binding (associated to a "cloud" of gluons joining together the three quarks) is responsible for ...
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If $E = mc^2$, doesn't that mean we relatively have infinite energy? [closed]

I was going through the energy/mass equation and it is said that both of the said quantities are interconvertible. That made me think that if we try putting actual values into the equation, the ...
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2 answers
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In what form is the binding energy released after nuclear fission?

This is too primitive question. but I cant find a definitive answer anywhere. Everywhere its mentioned that Binding energy is released in the good-ol uranium 235 and uranium 238 nuclear fission. Where ...
Rohit Shekhawat's user avatar
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1 answer
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'Elementary' particles (electrons) vs non-elementary particles (protons) regarding relativistic mass

Is there a possible slight difference between protons and electrons behaviour while they are accelerated at speeds that cause relativistic changes to their mass. Why am I asking that? Because for a ...
Krešimir Bradvica's user avatar
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0 answers
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BTZ partition function

I am unable to obtain the internal energy of the BTZ black hole. Recall its metric, which is given by \begin{align} ds^2=-N^2(r)dt^2+\frac{dr^2}{N^2(r)}+r^2\left(d\phi+N^\phi(r)dt\right)^2\,, \end{...
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1 vote
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Conservation of energy and loss of mass in nuclear radiation

I'm learning about mechanical energy from Kleppner and Kolenkow (second edition), and in Chapter 5 (section 5.10), they introduce the notion of conservation of energy and connect it to the Einstein ...
D Ford's user avatar
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4 answers
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Line of action of resultant force of two parallel forces

We take a rigid body as shown in the figure and apply two parallel forces (which do not have the same lines of action) at the ends of the body. Let us assume that $P>Q$. Now as we all know There ...
madness's user avatar
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On the assumption of the nucleus having only kinetic energy in the mass gap demonstration

I have an issue in a step of the demonstration of the mass gap in the nucleus: Suppose we have a collection of nucleons, particles that made the nucleus. If the nucleus is moving with some momentum $...
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Can doing positive work in a system add mass to it?

We know that doing work changes the internal energy of a system. If we transfer energy in the form of work to an isolated system, we cause a change, an increase in the internal energy. Work is force ...
user18398875's user avatar
4 votes
1 answer
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How to explain different, seemingly inconsistent, values for the mass of the alpha particle in different books?

I’m trying to calculate the energy of an $\alpha$ particle after the decay of Ra-226 following an example in a german school book and came across different values for the mass of an $\alpha$ particle. ...
Tobi's user avatar
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1 answer
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Invariant nature of mass and particle annihilation [closed]

Since mass is a Lorentz invariant, it can never change to preserve the vectorial nature of the four-momentum and the other four vectors. Thus the only interpretation of the energy-mass equation that I ...
GedankenExperimentalist's user avatar
7 votes
2 answers
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If I suddenly store a lot of energy in a small space, this induces spacetime curvature. Does that create gravitational potential energy?

Let us presume that I have a capacitor and suddenly charge it. This induces a (miniscule) spacetime curvature. Nearby objects would experience a gravitational attraction and by extension would have ...
Michael Stachowsky's user avatar
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Question regarding statement in Wald's book regarding the ADM energy-momentum four vector

In the discussion of Energy in Chapter 11 of Wald's book, Wald briefly talks about the ADM energy-momentum. In page 293, Wald states that it follows from the Einstein Evolution Equations that the ...
amateurrelativist's user avatar
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3 answers
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Does every photon have same momentum because they have same velocity $= c =3\times 10^{8}$ m/s?

I am new to Stack Exchange as well as physics. Momentum is $$p={\rm mass} \times {\rm velocity}=mv.$$ So, if a photon has rest mass $m=0$, [Also what is "rest" mass?], and $v$ is always $c$, ...
anukarma's user avatar
1 vote
3 answers
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Mass-Energy Equivalence and First Law of Thermodynamics

Einstein showed mass can be converted into energy and vice versa. $E=mc^2$ However, in school we are taught that according to the First Law of Thermodynamics, energy can neither be created nor ...
Carl Buckminster's user avatar
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Mass matter, energy and "massless matter"

This is perhaps a rather silly question, or rather a matter of convention, but I would like to hear arguments about the appropriateness of certain definitions. Traditionally, in chemistry and in pre-...
Davius's user avatar
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Why protons and neutrons don't have less mass than their constituents?

A system of gravitational attracted objects weight less than the sum of their individual masses because it needs energy to move them apart and overcome the gravitational attraction. Same is true for ...
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