# Questions tagged [energy]

Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding the [energy-conservation] tag if it is specifically about its conservation.

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### Is there a way to manually change the energy of a particle?

We have a relation, $E=h\nu$, where $\nu$ is the frequency and $E$ is the energy of any particle. If we have a function, $\psi$, that is an eigenstate of energy, the particle has a definite energy, ...
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### “Standard kinetic energy term of nonrelativistic quantum mechanics” $[\mathbf p\cdot \mathbf A + \mathbf A \cdot \mathbf p]$

On page 187 of Peskin and Schroeder, a certain term in an expression for the amplitude of an electron scattering from a classical magnetic vector potential is identified with “the contribution of the ...
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### Proof that minimum free energy corresponds to equilibrium

I've tried to derive the relation between free energy, $F$, and equilibrium of a closed system. From the derivation i've written below it seems that if $T$ is constant and the system can't exchange ...
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### Gear Ratio And Torque Relationship

suppose a gear teeth ratio of (1:10) >> then it is obvious that the smaller gear will be faster than the larger gear >> And the higher gear has more torque which means a higher ...
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### Does the vacuum really have infinite energy density?

I said: As far as I understand it quantum field theory says that the vacuum has an infinite energy density. r/AskPhysics RedditorAbstractAlgebruh said: But wouldn't that be due to the way we do the ...
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### What law of thermodynamics is broken here? [closed]

This question came in the Dhaka university admission exam 18-19. A heat engine in each cycle does positive work and loses energy as heat with no heat energy input. Which law of thermodynamics does the ...
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### Unable to make sense of - Heat, a form of energy [duplicate]

I have referred to some textbooks on Thermodynamics and they more or less explain heat in the following manner: Consider a system which has some energy content. In order to increase the energy content ...
1 vote
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### Nuclear fusion mass defect and energy production

In researching the topic of nuclear fusion, I have a few doubts related to the mass defect, 'negative' potential energy and resultant energy released as a by-product of nuclear fusion. When two ...
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### Can someone please explain energy of electrons in Bohr's model?

Energy of and electron is $$E = \text{kinetic energy} + \text{negative of potential energy}. \tag{eq-1}$$ But energy of electron in the $n$th orbital is also $$E = -\frac{13.6}{ n^2} \tag{eq-2}$$ ...
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### Why is angular momentum equal to mass times radius times velocity?

When momentum is mass times velocity, why is angular momentum mass times radius times velocity?
1 vote
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### How is the internal energy changed if an atom is charged?

I read this statement from an exam: A neutral carbon atom gains 4 electrons, this atom has a higher internal energy after the addition than before. I am not sure whether it is correct, in particular, ...
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### In an isothermal process there is no change in internal energy, but why in an isobaric one?

In an isothermal process, the heat Q added (which increases the temperature and internal energy) is exactly cancelled out by the work W done by the gas in the environment (which lowers the temperature ...
1 vote
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### Pressure wave speed $v=\sqrt{\frac{B}{\rho}}$ rearranged $\rho v^2=B$ is similar to kinetic energy: $E_k=\frac{1}{2}mv^2$. Is this a coincidence?

The speed of a Pressure wave speed is given by: $v = \sqrt{ \frac{B}{\rho}}$, which seems rearranged very similar to kinetic energy: $\rho v^2 = B$. How can this be understood, is this a coincidence? ...
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### Why does applying the kinetic energy operator to a free particle result in a divergent integral?

The wavefunction of a free particle is just $$\psi = Ae^{i(kx-\omega t)}$$ and when you plug this into the Schrodinger equation you get the dispersion relation $$E = \frac{\hbar^2 k^2}{2m}$$ However, ...
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### Energy and force relation

So in simple machine we apple less force with more displacement to exert same energy as the load need so if energy is related to tiredness i.e. more energy you lose more tired you feel but by applying ...
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### What's the amplitude of the energy loosing oscillator as a function of time?

The problem comes from 'introduction to classical mechanics' by David Morin. It is as follows: A chain with mass density $\sigma$ kg/m hangs from a spring with spring constant $k$. In the equilibrium ...
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### Energy as a function of half-life?

How much energy is released in the radioactive substance's decay of one cycle of its half life? I'd like the plot the energy released of a radioactive substance over time. What must I reference to ...
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### Angular Momentum Conservation and Conservation of Energy

A heavy solid sphere is thrown on a horizontal rough surface with initial velocity $u$ without rolling. What will be its speed, when it starts pure rolling motion? So using conservation of energy, I ...
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### Veritasium Electricity videos: where does the majority of energy really flow? [duplicate]

After watching Veritasium second video on electricity (references at the end), I have some doubts about where the majority of the energy flow actually happens. The reference experiment is the simple ...
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### Temperature and latitude

Currently I read this excerpt on a school power point that stated the following: " The sun is closer to the equator than the poles. Therefore the sun’s rays have less distance to travel to the ...
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### Why don't we consider the energy $E_{com}$ for a two body problem

While studying two interacting particles such as a Hydrogen atom, I learnt how to reduce the problem into two independent parts by using center of mass coordinates and the relative coordinates. The ...
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### When a solid is melting how do the potential energy and kinetic energy of the particles in the solid change?

When a solid is melting, does the kinectic energy and potential energy of the particles in the solid change? Will they remain the same or increase or decrease.
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### Does the Higgs field have an energy?

I have many questions about the notion of space. I learned that at the quantum level, energy became quantized and that the infinite sum of energy states can no longer be substitued by integrals (...
1 vote
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### Why Photon gas's Equation of State Diverges?

We know that, for Photon gas, the equation of state is given by $pV=\frac{1}{3}U$; where $p$ is the Pressure, $V$ is the Volume and $U$ is the Internal Energy of the Photon Gas. (see Equation of State ...
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### Centripetal Force question

Since no work is done in circular motion due to no change in kinetic energy (constant speed) and force being 90 degrees from displacement(centripetal force). Does that mean changing an object's ...
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### Why there is no unit of energy? [duplicate]

In the SI System (https://en.wikipedia.org/wiki/International_System_of_Units) there are 7 units, but no unit of energy, though this is surely the fundamental unit of physics. Yet the Joule is usually ...
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### Is it possible to convert gravitational energy directly into electrical energy?

It is possible to produce strong gravitational accelerations on the free electrons of a conductor in order to obtain electrical current. This allows the conversion of gravitational energy directly ...
We know the formula, $$m = m_0/(1-v^2/c^2)^{1/2}$$ since $v$ is usually way less than $c$, ($v^2/c^2$) is less than one which indicates a body's mass increases when it has a speed. Can someone please ...
The first law is usually given as: $dE = dQ + dW = TdS + PdV$ Sometimes the chemical potential energy is also included. But you can include way more potentials. These are some that I came up with:  ...