# 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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### Can a big mass defect make the mass negative?

Can two particles with small masses and a strong attractive interaction have a total negative mass when brought together? Let $m_1, m_2$ be the (rest) masses of two particles when infinitely distant. ...
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### Is a photon truly massless? [duplicate]

First of all, I am not a physicist or mathematician, not even a hobbyist but the following statements have always puzzled me: $E=mc^2$ A photon is a desecrated particle of energy. A photon is ...
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### If a proton transforms into a neutron by releasing a positron why should this process create more mass? [duplicate]

If waves can interfere and thats why cancel out or add up why we cannot think the same about the natterial feature called mass as in this explained example in the title of this posted question??Thanks ...
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### Why is the mass-energy graph for atomic mass $A=98$ not quadratic?

For fixed atomic mass $A$ and varying atomic number $Z,$ the mass of the nucleus is quadratic in $Z$. Were it possible for $Z$ to vary continuously, we'd have at most one local minimum. Since we are ...
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### Why the Sun has a higher temperature than humans?

Why the Sun has a higher temperature than humans if the energy/gramme of matter ratio of humans is greater than that of the Sun?
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1 vote
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### "Mass Shell" Condition on Euclidean Scalar Field

This is a basic qft question. I am looking for the condition on a free scalar $\phi$ of mass $m$ in Euclidean space such that it satisfies the Klein-Gordon equation. The Euclidean space Klein-Gordon ...
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### Does life erode Earth's mass over time?

Since life converts matter to energy, and there's no natural process that does the opposite (aside from supernovas), does this mean that the mass of our planet is gradually diminishing? I asked ...
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### Why does the mass-energy equivalence apply to binding energy when it is derived purely through kinematic means?

I understand that by defining the four velocity, multiplying it by the rest mass and taking the entire thing's norm we get $E^2=m^2+p^2$, but how does this apply to binding energy, or in general ...
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### Is the Planck mass the "lower limit" for gravity?

The Planck units are often treated as being the "lower limits" to things: the Planck length for length, the Planck time for time, etc. But the Planck mass, which is about $2.2\times10^{-5}$ ...
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### How does mass-energy equivalence work with chemical bonds? [duplicate]

If you have, for instance, 2 oxygen atoms and do E=mc2 to get their equivalent energy, you get about 2.38nJ. However, if you have diatomic oxygen, there's also the energy of the bond; about 0.8aJ. ...
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### What is the total mass-energy of baryonic matter?

From what I understand, conservation of energy does not apply to the total energy of the Universe, because it constantly expands and the new, created space has a constant non-zero energy of its own. ...
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### Rest Mass Energy

What exactly is the Rest mass energy? I know the usual goes Like it is total energy stored in mass $m$ that is in Rest. so for someone moving relative to the frame that the mass $m$ is in (a rest ...
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### Does dark matter have mass?

When trying to understand what dark matter is, it is helpful to know that some properties of it can already be derived from various observations, such as, it only interacting via gravity and no other ...
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### Suppose a shell of a sphere formed by matter and with large radius, start afterwards to diminish the radius, give $E=mc^2$ the system stops

Thinking in classical mechanics terms but with the knowledge that $E=mc^2$ let's make the below thought: Suppose you have a shell of a sphere formed by a mass uniformly distributed over the surface of ...
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### Is the relativistic energy-momentum relation fundamental? [duplicate]

The following relativistic energy-momentum relationship is taken to be fundamental: $$E^2=p^2c^2+m_0^2c^4.\tag{1}$$ Let us specialize to massless particles ($m_0=0$) so that we have: $$E=p\ c.\tag{2}$$...
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### If a 100,000 ton container ship slams into a bridge at 8.6 knots how much energy was moved into the pylon and at what rate of transfer speed? [closed]

Edit: the entire question is in the title, the answer should be an amount of energy and a value of energy transfer in some unit, but not knowing enough about physics I don’t know what the appropriate ...
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### If I burn a log & contain all the matter, will the burned log weigh $E/c^2$ less than the unburned log, with $E$ being the energy from light & heat? [duplicate]

I understand that the change in weight would be tiny even to a physicist and nothing for any practical purpose. I am also not talking about smoke and water vapor. I am only referring to energy given ...
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### Why does the total gravitational potential in the universe exactly equal the total mass energy RIGHT NOW? [duplicate]

In the zero energy universe model, the gravitational field has negative energy, and this negative gravitational energy of all the distant mass exactly balances and cancels the positive mass-energy in ...
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### How mass change can be converted to energy? [closed]

Some gas with initial mass $m_{1}$ was put in a container under high pressure and temperature. After some time its mass became a bit smaller ($m_2$). Additionally, some energy was released and it was ...
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### How can a proton be stable if binding energy *increases* it's mass? [duplicate]

A hydrogen atom weighs 13.6eV less than a proton + electron. This missing energy, which is tiny compared to the rest mass of almost a GeV, was carried off by a photon when the atom formed. Nuclei show ...
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### What is the causation of the mass deficit in atomic nuclei?

I've always heard that when protons and neutrons are combined together into nuclei, the mass of the product is less than the mass of the constituents. And that this mass is called the mass deficit and ...
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### If matter is a form of energy, can it be converted into another form of energy?

I have been told that energy and mass are the same. What puzzles me is why don't we use the same units of measure for both if they are the same? The unit of mass is kg and the unit of energy is the ...
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### Mass self-annihilates to violate law of conservation of energy? [closed]

The scenario is this: a large mass $M$ is made of matter and anti-matter in equal amounts. If given a little energy, it will self-annihilate. Another mass $m$ is in vicinity. The potential energy ...
1 vote
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### Why do ( within my limited understanding.) Energy and matter act in opposite ways [closed]

I would like to preface this by stating this type of research is my hobby not my profession. If I understand the basic explanation correctly, energy tends to spread out evenly within a closed system ...
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### Is there a unified conceptual definition of mass?

Last night I posted this question: Since light has inertia and experiences gravity, what does it mean for photons to be massless?, which I now think was overly wordy and didn't properly express what I ...
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### How to find rest mass?

I have two identical massess with rest mass $m_0$. One of them is made to move with very high velocity $v$, while other is at rest. At some point in time the moving mass collides with the stationary ...
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### Since light has inertia and experiences gravity, what does it mean for photons to be massless?

I've been trying for a long time to figure out what the heck mass even IS. In introductory physics and chemistry, students are told that massive objects are those that are made of matter and take up ...
1 vote
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### In special relativity, is mass considered as $\gamma m$ or is only the momentum considered as $\gamma mv$?

I am trying to solve the equation of motion of free-falling object considering relativistic effects. I am not sure the force on the object is whether $\gamma mg$ or just $mg$ where $m$ is the rest ...
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### Why it is the mass instead of the mass distribution used in Schwarzschild metric?

Schwarzschild metric is given by (Carroll, chapter 5) $$ds^2=-\left(1-\frac{2GM}{r}\right)\mathrm{d}t^2+\left(1-\frac{2GM}{r}\right)^{-1}\mathrm{d}r^2+r^2d\Omega^2$$ where $M$ is the total mass of a ...
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