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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When we say particle in a box has quantized energy, is that kinetic or total energy?
In quantum mechanics, it is usually said that energy of the bound (constrained) systems such as particle in a box (infinite potential well) is quantized. It confuses me exactly what type of energy is ...
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How can gravitational waves dissipate the energy carried by them? [duplicate]
I am not an expert on GR or gravitational waves but i have been reading about them and i wondered about where and how do these gravitational waves dump their energy? I read that the black hole ...
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Why does the Gravitational Potential energy formula indicate that heavier masses in the same point in the field have lower potentials?
$$ U = -\frac{Gmm_E}{r} $$
Intuitively, it'd appear that the further away two objects are, the greater their gravitational potential, and this is confirmed by the gravitational potential formula. The ...
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Are energy and momentum separable for EM waves
Everywhere I get to read statements like EM radiations and EM fields carry "energy as well as momentum " . I wonder if energy and momentum are inalienable . Is it possible for a field to carry only ...
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What is negative energy?
From what I've read negative energy is based on the Dirac sea concept of virtual particles. Negative energy is referenced by Casimir effects of virtual particle concentration differences between the ...
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Perpetual Mobile and Gravitation
I have fundamental question about what is called the “law of conservation of energy”.
We all hear about the tidal power stations which using the tidal power. The source of the tidal power came from ...
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Negative Energy in Inflation Theory (Low/Zero Energy Universe)
I've been reading Max Tegmark's book: Our Mathematical Universe. It's very interesting, but I wanted to know more about one particular thing. The book simplifies things and I know inflation theories ...
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Sufficient conditions for the energy to be not conserved?
I'm almost embarrased to ask this question because I thought I was by now very confident with classical mechanics.
Someone has stated that given a mechanical system with a Lagrangian $L$ s.t. $\frac{...
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If the energy of an ant is smaller than an elephant, does that mean the ant is more stable than the elephant?
I know that when a system is in its lowest level of energy, it is most stable. However, what if system 1 has lower energy than system 2, does it keep meaning so? Or do we need to examine their binding ...
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Estimating minimum energy with uncertainty principle
I'm currently trying to solve a problem that involves estimating the minimum energy of a particle in the potential:
$$
V(x) = \frac{-V_0a}{|{x}|}
$$
I'm quite confused about how to handle the ...
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Vacuum energy extraction: What happens to the cosmological constant?
If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same? .
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Energy of electron spinning in a magnetic field
When an electron travels in circles in a uniform magnetic field, it must lose energy because all accelerated charges radiate, and must therefore spiral down to the center. Is this energy compensated ...
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Elastic collision and spring
Bodies $A$ and $B$ are moving in the same direction in a straight line with a constant velocities on a frictionless surface. The mass and the velocity of $A$ are $2 \text{kg}$ and $10 \text{m/s}$. The ...
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What is meant by positive and negative gravity/energy/spacetime-curvature?
I have recently come across some cosmological assertions (based on empirical data) about the universe being self contained in the sense that it is entirely capable of coming into existence from a zero-...
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When matter and anti-matter collide
Do they create energy? Or do they just disappear with zero energy?
If they create energy when disappearing, that means it takes energy to create them, right?
If they disappear into zero energy, ...
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Energy in electric field of an electron?
I am just trying to get an intuition for the Griffiths equation no. 2.45, where work done to establish a field E is given by
Say we want to solve it for electric field due to an electron (point-charge)...
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Origination of electromagnetic wave energy
Please correct me if I am wrong in my statements
While it is said that electromagnetic waves are formed by the oscillation (acceleration) of charges which forms 'kinks' in their electric field which ...
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Why is the ratio of components of kinetic energy equal to the ratio of kinetic energy to total energy for a projectile whose range is maximized?
The launch angle $\theta$ that maximizes the range of a projectile in a uniform gravitational field is
\begin{align}
\theta = \arctan\left(\frac{v_o}{\sqrt{v_o^2 + 2gh}}\right), \tag{1}
\end{align}
...
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Gibbs-Duhem equation and homogeneous function of mixed Euler order
My question is related to this article by Sorensen and Compan. The usual definition of an homogeneous function of order $\mathcal M$ is by the equation $f(\lambda \mathbf{x}) = \lambda^{\mathcal M} f(\...
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How can a system with a given temperature, volume and number of particles have many possible microstates of different internal energies?
I am learning about the canonical ensemble where a system in contact with a heat reservior is considered. The objective is to find the probabilty of the system having the microstate marked by a ...
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Particle production in an expanding universe?
I was reading this interesting article which talks about particle production in an expanding universe.
Usually this process is proposed to have occurred in the early universe, when the expansion was ...
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What is the relation between the free energy and the action? More generally, what is the relation between Thermodynamics and Lagrangian Mechanics?
My question stems from the sentence said by my professor "The action is the free energy" which I don't understand. Thinking that probably I'm missing some key concepts, I'd like to know: ...
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Why is the energy of a vortex in a superconductor finite?
I just had a glimpse of the Ginzburg-Landau theory of superconductivity. I am surprised that that the energy of a vortex is finite. This is surprising because as far as I know, in superfluids, the ...
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An absurdly complicated, simple force problem
In my high school physics class, we're learning about analyzing force diagrams, with quite simple problems about blocks sliding down ramps. One of my friends decided to parody the hilarious "realism" ...
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Average kinetic energy in 1 dimension according to Maxwell-Boltzmann Distribution
The format of the 3 dimensional MB distribution is $A \cdot e^{-\frac{E}{k_BT}} \cdot g(E)$ in which $A$ can be derived using normalization (integration up to $\infty$ must be 1) and $g(E)$ being the ...
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Physical significance of free energy in canonical ensemble?
From macroscopic thermodynamics I understand that the free energy equals the total energy of the system minus the energy it would have cost a thermal reservoir to create it. So any energy in "excess" ...
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We just need a solar panelled SPAIN to power the world? [closed]
A stiffer, more formal (form, schmform!) way to ask this is:
Is a solar panel field the size of Spain enough to cover the worlds energy needs?
(This assumes that everything in the world runs on ...
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Relative potential energy vs Absolute potential energy
I have seen in many textbooks and sources which say that we can't experimentally measure potential energy but we can measure differences in potential energy.
$$\Delta U_g=-W_g$$
Choosing zero ...
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A question about magnets, energy, and forces [duplicate]
Following my first lecture on magnetism today, I'm left with just one question my lecturer couldn't answer.
Imagine a 1 kg magnet supporting its own weight stuck to a vertical surface, resisting ...
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Work done by a magnetostatic field [duplicate]
How does a (static) magnetic field accelerate objects (like an iron nail) if we are taught that the magnetic force does always zero work?
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Speaker energy mystery
Speaker power consumption quadruples when producing sound with double amplitude.
Two speakers consume two times the energy of single speaker.
Two speakers playing signal in phase double the sound ...
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What is the third peak in the spectrum of Sodium-22?
I collected this spectrum from a sodium-22 sample in an instructional laboratory. The sample was set in front of a germanium detector which sends a signal into a pulse height analyzer and plots a ...
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Capacitor with a dielectric with only one plate / with one plate moving
I was wondering how a capacitor like the one in the picture below works. The length of the plates is L and their width is b (parallel to the z axis). The distance between the plates is d. The whole ...
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Energy of a particle as measured by an observer at infinity
I'm wondering if it is possible to make a definition for the energy of a particle as measured by an observer at infinity. I've looked through Wald for this but wasn't able to find anything - I may be ...
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What is the abstract idea behind energy? [duplicate]
Many theories use something called energy to explain reason behind certain phenomenon, but I have not been able to grasp the idea of energy. Maybe it is because I have grown in a society where the ...
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Dissipation and first law of thermodynamics
Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
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Smallest Wavelength of light possible? [duplicate]
I was thinking about blue-shifting of light and I couldn't help my self but think about the limits of blue shifting mechanism and since we know energy of a photon is directly proportional to the ...
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Does or should the metric expansion of space imply a locally observable increase in kinetic energy?
The title is the question. Here's why it seems like local kinetic energy should increase:
Numerous questions and answers here and elsewhere suggest that the reason the metric expansion of space is ...
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What is energy? [duplicate]
What exactly is energy (in terms a non-physicist/non-mathematician can understand)? I've been researching this topic, and it seems that energy is not a real physical state, i.e. it is only a scalar ...
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What are the forms of energy at fundamental level? [closed]
Most high school textbooks distinguish several forms of energy.
Mechanical:
-Kinetic
-Potential
Chemical
Electromagnetic
Nuclear
Gravitational
Thermal
Hydraulic
Electric
Mass
...
This ...
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When Hamiltonian and the total energy are the same
In which condition, the Hamiltonian is the same as the total energy of the system, or say $H=T+V$?
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Is there a finite amount of mass in the universe? [duplicate]
So, I'm not too physics savvy but I am curious to ask. Is there a finite amount of mass in the universe? or is there more and more being created from somewhere or something? If the universe is ...
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How to convert Richter magnitude scale to approximate TNT?
I know the Richter magnitude scale is often used for measuring the strength of earthquakes. At the same time, explosive/destructive releases of energy are often quoted in equivalent amounts of TNT. Is ...
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How much energy is radiated when matter falls into a black hole
When a black hole consumes matter, it can form an accretion disc. Is there a relationship between the mass of the falling matter $m$, the mass of the black hole $M$, and the energy radiated during the ...
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What are the other ways of energy transfer apart from heat and work?
In my physics textbook I've seen that heat and work are non mechanical and mechanical forms of transfer of energy. Why can't electrical or chemical or nuclear energy or energies like that be a form of ...
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Why don't we get infinite energy from a continous emission spectrum?
If the spectrum emitted contains all kinds of photons of all kinds of wavelengths, doesn't that mean it should have infinite number of photons of very small energies? For example, 4000 angstrom to ...
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Why do we say that gravity did work on an object to give it velocity, when it already had that energy as a potential?
I'm having a crisis of intuition here.
Scenario
A person takes a dive from a cliff. The person has a potential energy of $E_p = mgh$. As the person falls, they build kinetic energy, and lose potential ...
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Why do almost all nuclear reactions release energy?
I'm just wondering why almost all nuclear reactions release energy, in a typical way, the mass defect is transformed into energy ? Is there a nuclear reaction that gains mass (resp. energy)? or most ...
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How can the Klein-Gordon equation have negative-energy solution if its Hamiltonian is positive-definite?
In a lesson about the introduction of classical field theory it was mentioned the Klein-Gordon equation
$$(\Box + m^2) \phi(x) = 0. \tag{1}$$
But before we got this equation, we studied the ...
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Why is the total electrostatic energy bigger than the sum of separate energies?
I don't understand why, if we add the two energies $\,\boxed{1}\,$ and $\,\boxed{2}\,$ from two electric fields, the component $\,\boxed{3}\,$ is added and so it's different from their sum
\begin{...
