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 [tag:energy-conservation] if it is specifically about its conservation.

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Why is there zero point energy at absolute zero temperature?

If we define the absolute zero as a temperature which there is no entropy in it so why should we have zero point energy?
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What is the connection between Bragg's condition with reduced EK diagram?

In my course notes the professor mentioned that there was some relationship between the Bragg's condition and the first Bernoulli zone of the reduced EK diagram. Specifically, the boundary before ...
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Why is energy in a system typically able to be described using quadratic expressions?

This might be more of an applied math question. Why is the energy of a system typically able to be described using quadratic expressions. Is there an underlying mechanic that drives this?
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Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [duplicate]

I want to know the configuration where the system would be most stable.I only know basic Physics & Maths and cannot start solving the problem.I can understand it for 4 charges and 6 charges as a ...
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47 views

Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [on hold]

I want to know the configuration where the system would be most stable. But I cannot think of a way to start solving the problem. I've solved it for 4 charges and 6 charges and they have a symmetric ...
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1answer
24 views

Is it possible to make use of the gluon field's energy to use is applications?

As we know most of the mass of the proton comes from the energy caused due to the interactions of the quarks with the gluon fields (reference link of this statement ...
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1answer
49 views

Do Waves have mass? [duplicate]

Do any form of electromagnetic waves like visible light have mass? It is known that all electromagnetic waves have energy. According to Einstein's $$ E^2=p^2c^2 + m^2c^4 $$ formula, the energy of a ...
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379 views

Is it possible to generate energy by the moon orbit?

My question could be a little bit surreal, but I was thinking about this: A hydroeletric plant transform the energy from the water passing through the turbines into electricity. Correct? If the ...
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1answer
69 views

Massless particle that have momentum not equal to 0

I saw some problems in special relativity that use conservation of total energy and momentum and the conclusions are spectacular. My problem is the following: how can a massless particle like neutrino ...
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3answers
60 views

Work-Energy conservation with friction

I didn't go to the lesson of work-energy theorem, so I miss something about this subject. I know the formulas, but I can't figure it out. This question has many quantities. Here is the problem, ...
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2answers
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What would happen to a star if a Dyson sphere lined with mirrors reflected a significant portion of the stars light back to the star

I have looked for similar questions here on stack exchange. The closest example to this that I found is Could a Dyson sphere destroy a star. That question assumed less than perfect absorption of ...
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Particle moving under force $F=-cx^3$ [on hold]

A particle with mass $m$ moves under influence of a force $F=-cx^3$, with $c$ a constant. What is the potential energy function $V(x)$? And if it starts to move from rest from position $x=-a$, what ...
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1answer
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How do you define the total rotational energy of an object?

This problem arose when I was applying a conservation of energy argument to a mechanics problem, (a spinning coin on a table) and wasn't sure how to define the total rotational energy of the coin. At ...
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Conservation of thermal energy [on hold]

A 2 kg block of ice's temperature is 0 degrees C. It is put into a 10 kg sample of water at 5 degrees C. What mass of the water is melted when thermal equilibrium is reached? I know it has to do ...
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2answers
49 views

Car motor heat to drive a steam engine

Why wouldn't be able to place a car motor inside a water tank or another liquid to be heated by the motor, instead of wasting the heat and then use the steam generated, to drive a steam engine, which ...
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1answer
42 views

Does gravity (and all other fundamental forces, for that matter) have infinite energy as they seemingly last forever? [duplicate]

If I put a brick onto an steel platform, that platform can hold the brick A LONG TIME, if not FOREVER. Does the platform exert force? If so, then shouldn't it have infinite energy to resist the pull ...
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1answer
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Polarized Filtering Frequency Shift?

A polarized filter is exposed to a unpolarized light source. The output of the filter should be of lower intensity, hence lower energy. Should not the filtered light be of a lower frequency to ...
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2answers
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How does matter get the energy to repel the gravitational effects of itself to to other matter

This has always puzzled me. As i stand on the earth i require energy to exert a force over gravity to enable me to keep standing. The net force between me and the the earth is zero and thus i remain ...
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1answer
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How to light a bulb with a kite? [on hold]

I need to make a kite from biodegradable materials. The kite must be able to generate enough energy to light a led. Any ideas?
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Is this the energy balance for this problem? [on hold]

I am working on a school project and I have to cool equipment that are in an enclosure that is in the living room of a house. I have an exhaust fan that draws cold air from outside the house (ambient) ...
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2answers
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Calculate required power output for a laser

How to calculate power rating required for a laser in order to produce a dot at a specific distance after reflection? For example, the laser is 10cm from the mirror, at an angel of 30 degrees it ...
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4answers
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Different kinds of energies in the form of $\frac{a_1a_2^2}{2}$

It seems to me that the energy of some kind frequently takes the form $$\frac{a_1a_2^2}{2}$$ Where $a_1$ and $a_2$ are some variables. So, for example, kinetic energy has $m$ and $v$; rotational ...
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Why aren't we affected by radium?

1)We have radium clocks, watches, wrist bands and many things which glow because of radium but we know that radium is radioactive so why isn't it harmfull for us when in bands, watches etc. 2)Does it ...
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When moving from one position to another at a constant velocity, how does the conservation of energy hold?

I know that this might be a duplicate question, but I have not found any satisfactory answers that clear up my lack of understanding. Here is my question. Say a sloth hangs on a tree in the middle of ...
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1answer
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Can the Cosmic Neutrino Background be detected from a lab moving near the speed of light?

If I've understood it correctly, the energy of an object depends on the reference frame, so when you accelerate, the CMB and CNB appear to gain energy (relative to your rest frame). So if you are ...
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1answer
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Can a solar panel work with heat?

As we know that a solar panels due to the energy of light, but can we run a solar panel with the same amount of energy provided as heat?
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What theories or formulas are involved with velocity

What theories or formulas are involved or can be added as background information in an experiment that sees a small toy car roll freely down an incline where the surface area is altered to cause more ...
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Lack of rigour in usual derivation of Work-Energy Theorem

The derivation of the Work-Energy theorem usually goes as follows: You define the work done on a particle under net force $\vec{F}$ as $$W=\int\limits_C \vec{F}\cdot\mathrm{d}\vec{r}$$ And then you ...
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3answers
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Work and energy

when a ball of mass m is brought with uniform velocity from infinity into the g field of the earth at a distance r from it, the potential energy of the ball earth system decreases from 0 to -GMm/r. ...
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1answer
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What factors affect the velocity of an object moving down an inclined plane?

If you have a small toy car rolling down an wooden plank, what factors would increase or decrease the velocity of said car. In the experiment my team originally stated that adding mass to the car ...
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Total Energy of Inverted Pendulum

I have to find the total energy $V$ of an inverted pendulum (rod). The following parameters and their values are given: Mass $m$ and length $l$ of the pendulum $\theta$ as the angle of the ...
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1answer
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“Definition” of internal energy

Conversation of energy implies that if we have a thermally insulated system which goes from state 1 to state 2: $$\Delta E_{12}=E(2)-E(1)=\Delta W_{12}$$ and the 1st law of thermodynamics ...
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Why does moving through time not require energy?

Moving through the other three dimensions necessitates energy. But why doesn't moving through time necessitate energy?
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Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
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Experiment validating existence of virtual particle

I'm curious about virtual particle whether do they really exists, therefore I dug out an experimental theory called lamb shift by measuring the difference between the two energy levels of a hydrogen ...
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Absortion of light by a plasma

Considering a plasma generated in a fixed volume by increasing the temperature of Helium gas from the environment temperature (this temperature is not stated) and an initial presure of 0.001 Torr, to ...
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Does it take more energy to open a door when applying force close to the hinge?

Assuming an ordinary hinged door (without any springs), would it take more energy to open it when applying force in the middle of the door (point b), rather than at the end of the door (point a), ...
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3answers
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Closed-system power-generation using waterwheels

I'm not a physicist, and this question is bugging me .. :) Is it possible to create a closed power-generation system, using upper and lower water-reservoirs where a continuous flow from the upper to ...
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1answer
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4-momentum of massless photons

The time component of a particle's 4-momentum is $$ E'=\frac{E-up}{\sqrt{1-u^2/c^2}}\tag{1} $$ Now suppose it is photons that you are observing from a system moving at $u$ on a line towards ...
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Why doesn't the evening/morning sun feel much hotter on your face?

I understand that places on the Earth's surface get hotter in summer, and in the middle of the day rather than morning or evening, because the surface of the Earth is presented 'face-on' to the Sun at ...
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1answer
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Series of parallel thermal resistance connection for this enclosure?

Let's say that I have an 2D enclosure in the shape of a pyramid with unequal areas for the faces and I am looking to determine in the inside air temperature. The parameters I know are the outer and ...
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1answer
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If we hit an electron will it go to an excited state?

For example i have a block of silicon doped with phosphorous and i hit it hard with a hammer will the energy get transfered to the block and make the electrons excited?
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How does a photon drive out the electrons in a solar cell?

We know that solar cells work when a photon hits the n-type the photon's energy drives free the electrons in the n-type to generate a current. But we also know that when a photon hits the atoms it ...
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2answers
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Energy conservation $\iff \frac{dE}{dt} = 0\ $?

If I'm asked to prove that a system is/ isn't conservative and compare it to whether or not the Hamiltonian is conserved, does that mean I need to compute the time derivative of energy $(T+U)$? Doing ...
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2answers
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How did Planck derive his formula $E=hf$?

Some time ago I asked my quantum physics lecturer the question: How did Planck derive his formula, the Planck–Einstein relation $$E=hf$$ with constant of proportionality $h$, the Planck ...
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Maximum Extension of a Spring [closed]

In the given figure: m= 5kg, F = 30N, K = 700N/m In the figure shown above. the surfaces are friction-less. The blocks are initially at rest and the spring is initially in its natural length. What ...
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Identity operator in terms of the energy eigenstates in case of continuous spectrum

Let us confine ourselves to the 1d case. If we define the momentum eigenvector $|k\rangle $ as $$ \langle x |k\rangle = \frac{1}{\sqrt{2\pi}} e^{i k x} ,$$ we have the identity operator decomposed ...
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Potential and kinetic energy

If a ball stays on the ground, it has no height and no velocity. So what energy does it have kinetic or potential?
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Calculate energy-density of known plasma in microwave?

Let's assume I want to create a plasma in a regular household microwave similar to this home-made experiment. Although I am dealing with a small amount of mass, I assume that the addition of microwave ...
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1answer
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Why can “slow” neutrons trigger fission?

My understanding of nuclear fission is that some massive isotopes such as uranium-235 are unstable and when split via fission there will be a "slow" neutron. This slow neutron will hit another ...