# 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?
1 vote
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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 ...
27 views

### 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?
53 views

### 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 ...
129 views

### 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 ...
41 views

### 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 ...
1 vote
44 views

### 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?
175 views

### 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 ...
68 views

### 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 ...
43 views

### 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-...
107 views

### 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 ...
1 vote
68 views

### 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 ...
146 views

### 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 ... 50 views

### 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 ...
349 views

### 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 ...
56 views

### 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 ...
1 vote
844 views

### 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 ...
70 views

### 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 ...
1 vote
51 views

### 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 ...
1 vote
52 views

### 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 ...
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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'...
2k views