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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Energy spent by motor in a period

Consider a single coil that is turning in a constant and uniform magnetic field thanks to a motor. The normal to the coil is given by: $${\bf u}(t)=\sin (\omega t){\bf u_x}+\cos(\omega t){\bf u_z}$$ ...
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Proof of conservation of energy?

How is it proved to be always true? It's a fundamental principle in Physics, that is based on all of our currents observations of multiple systems in the universe, is it always true to all systems? ...
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0answers
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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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2answers
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Is the total mass of the universe constant in time? [duplicate]

Is the total mass of the universe constant in time?
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2answers
553 views

“Correlation energy” using the pair correlation function

In this paper on the Quantum Hall effect the authors refer to something called the correlation energy of electrons. It is defined at the top of page 5 as $E=\frac{n}{2}\int (g(r)-1)V(r)dA\ ,$ where ...
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2answers
549 views

How much faster is the fusion we make on earth compared to the fusion that happens in the sun?

I have come across many websites that states that the proton-proton fusion which is the dominant type of fusion that powers the suns, is extremely slow and that is why the sun is still burning to that ...
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1answer
77 views

We create systems with different values of Energy? [closed]

I understand that Energy is a conserved quantity in a system. A number, that's always the same to the system. However, don't we determine such a number? I mean, we can create systems(Or study them ...
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1answer
116 views

Can it require different amounts of energy to generate the same impulse?

According to impulse principle the impulse is the same as the change in the object's momentum: $\bar I = \delta p$ Because the momentum can be calculated like this: $\bar p = m\bar v$. If we solve ...
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3answers
537 views

Shouldn't the sign of generated entropy always be positive?

I have a process where 10 g of liquid lead at 400 C is dropped into a water bath that is at 25 C. The lead solidifies over time and comes to thermal equilibrium with the water bath. The bath is so ...
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0answers
485 views

Making an equal amount of positive and negative energy?

I was wondering if it would be possible to create an amount of positive energy out of a vacuum, in addition to an equal amount of negative energy, thus not violating the first law of thermodynamics, ...
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1answer
45 views

Propulsion Energy in Special Relativity

I have a question regarding how to calculate the energy required to move objects within the frame of special relativity. To that extent, I understand the mass of an object as it approaches the speed ...
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1answer
138 views

How is the energy of a lightning calculated?

I was wondering how is the energy of a lightning measured? Is it based on the luminous intensity and/or the generated sound? What about the generated heat and energy spent in the production of ozone? ...
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4answers
3k views

Does light loses its energy when it passes through denser medium

I know it does not because it emerges out of denser medium at 300,000 KM per second, but according to E=MC square and given that speed of light decreases inside denser medium with refractive index ...
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0answers
59 views

Kaon spontaneously splits into two pions (just need an confirmation)

I just need a confirmation on a problem that I am dealing. In my problem I have a statioary kaon which spontaenously splits into two pions which are headed in different directions. Is it possible to ...
2
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1answer
442 views

A dielectric table is being inserted between a plate capacitor and $\triangle U<0$ how to deduce the table is attracted to the plates?

I am practicing for an exam in my Physics $2$ course. One of a previews exam questions described a plate capacitor and asked to calculate the initial energy $U_{0}$, then a dielectric table was ...
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0answers
53 views

How do you determine the energy of an isotope?

How do you determine the energy of an isotope? I there a calculation for it? Sorry for the confusion
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2answers
134 views

what is “work”? (of a force)

I would like to know why two forces (of different magnitudes but same direction) that we'd use sequentially on an object to move it by the same amount twice, will produce two different values for the ...
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2answers
540 views

Elastic potential energy of compressed spring? [duplicate]

If a compressed spring is dissolved in acid what happens to the elastic potential energy of the spring?
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2answers
6k views

Why can't we destroy energy?

From a wikipedia article: In physics, the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. Energy can be neither ...
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1answer
203 views

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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6answers
17k views

Where does gravity get its energy from?

I would like to know where gravity gets its energy to attract physical bodies? I know that the law of conservation states that total energy of an isolated system cannot change. So gravity has to be ...
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1answer
291 views

Can magnetic energy be used to create a magnetic motor which can power vehicles and machines? [closed]

Can magnetic energy be used to create a magnetic motor which can power vehicles and machines?
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2answers
264 views

How much more energy would I spend if my bicycle was 2 kilos heavier? [closed]

I have a bicycle weighing 8 kilos. An 10 kilometer ride averaging 20 km/h requires z kWh's of energy. How much more energy would I spend if I added 2 kilos to my ...
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3answers
6k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
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0answers
64 views

what are the main factors holding back magnetic energy storage systems?

Perhaps is it the magnet's own magnetic field that causes it to lose its superconductive state? It seems as though these systems could become incredible energy dense.
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1answer
220 views

Does a 27 hp engine output the same amount of energy as lifting a 1 ton stone block almost 3 meters per second?

I’m trying to get a sense of how much energy a 27 horsepower engine outputs. 27 hp $=$ 20 133 watts (joules/second). Potential energy can be calculated as $E = mgh$ where $g = ~9.8\ m/s^2$ on earth. ...
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1answer
421 views

How is the energy distributed in a proton-antiprotion annihilation?

I know the products of the annihilation, but I don't know how much energy each particle has or gets. For example I know that 1876 MeV is released for each annihilation. Now, this energy is distributed ...
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0answers
173 views

What causes an electron to return from a higher orbit to a lower orbit

Ultraviolet light can cause electrons from Hydrogen gas to jump from a lower energy orbit to a higher energy orbit. What causes the electrons to return from the higher energy orbit to the lower energy ...
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3answers
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Energy needed for Superman to take off and fly at the speed of sound

I just watched "Man of Steel", and I'm wondering if my logic is correct. Let's assume Superman is 80 kg. The energy required to take off from the rest to reach the speed of sound in air (if I neglect ...
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2answers
3k views

How to transform mechanical work into electrical energy without using piezoelectricity?

can someone help me with the following issue. I need a method for transforming mechanical work into electrical energy without using piezoelectricity. I have such kind of mechanical forces (like on the ...
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0answers
79 views

Where does the relation $u=h_f-RT+(c_p-R)(T-T_0)$ come from?

I'm working on a college project for a subject called Motorcycle Engineering, and in this project I'm supposed to do some reverse engineering on a MATLAB program to model the engine of the motorcycle. ...
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2answers
599 views

What is the percentage of useful energy do we get from matter-antimatter annihilation?

This is a theoretical question since we haven't made enough antimatter to try it in reality of course. But I am asking about the physics part in this. Also, by "useful energy" I mean the energy we ...
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3answers
29k views

Why is Energy = Voltage x Charge, and how to prove that?

As you know the equation $\mathbf{E=V\times Q}$. Where: $\mathbf E$ is the energy measured in joules, $\mathbf V$ is potential difference (Voltage), $\mathbf Q$ is the charge. So my qustion is: ...
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3answers
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Can antimatter be used as fuel for nuclear reactors?

I completely understand the difficulties of making and storing antimatter, so I am not talking about the mechanism or the way of doing it here, I am just talking about the concept. As far as I know, ...
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2answers
1k views

The Quantization of Photon Energies [duplicate]

Despite Planck's constant being in $E=hf$, it would appear to me that energy is still not discrete, as frequency can be an fraction of a Hertz that one wants. How does this imply that electromagnetic ...
2
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1answer
648 views

Diagonalization of a hamiltonian for a quantum wire with proximity-induced superconductivity

I'm trying to diagonalize the Hamiltonian for a 1D wire with proximity-induced superconductivity. In the case without a superconductor it's all fine. However, with a superconductor I don't get the ...
0
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1answer
115 views

energy efficiency, transformation from chemical to thermal energy, for district heating plants

If I have a system in which I introduce 100e.u.F (energy units) derived from chemical energy (i.e. fuel) and generate thermal energy to heat water what are e.u. absorbed by water? I.e. the efficiency ...
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0answers
26 views

What are physical effects that could be employed to emulate this system?

This is a simple system consisting of a tree of numbers such as ((1 2 (3 4)) (2 6) 1 6) and a rule of application, that states that a tree A applied to B is a copy ...
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2answers
4k views

The Energy Eigenvalue of a Wavefunction

I've been reading an introduction to quantum mechanics online, and while constructing the Schrodinger equation for a free particle, the equation $i\hbar \frac{d \Psi}{dt}=\hbar\omega\Psi$ is obtained. ...
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3answers
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In nuclear fusion reaction, what is the percentage of mass converted to energy?

I read somewhere that it is about one percent of the mass, but I find this too high. Also I have done some calculations, for example, the Tsar Bomba was 50 MT bomb and weighed about 27 tons. Although ...
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0answers
56 views

What highest amount of energy can we get from a laser?

Can we get high energy from laser like fusion and fission reactions ? what is highest energy we can get from laser ?
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2answers
217 views

Can an Incandescent Bulb be considered as a heater?

Due to an experiment, I need a small heater (around 70 to 100 watts). I intend to use an incandescent bulb so it can act as a heater. What I wonder here is will a 70 watts Incandescent Bulb be equal ...
1
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1answer
1k views

Can electromagnetic radiation (i.e. photons) produce gravity? [duplicate]

I don't want to play with physical laws in a frivolous way. Assuming that the nature of matter and energy is the same, can a high density of highly energetic photons produce a gravity force? We do ...
7
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3answers
922 views

Connection between $\Delta x \Delta p \geq \frac{\hbar}{2}$ and $\Delta E \Delta t \geq \frac{\hbar}{2}$

Is there a way to derive second equation from the first one? I mean is there a connection between those two uncertainty relations? \begin{align} \Delta x \Delta p &\geq \frac{\hbar}{2}\\ \Delta ...
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0answers
169 views

Collision of two deformable bodies - limitation of work-energy theorem

I am attempting to model the impact of a deformable body (clean, dry sand characterized as a continuous fluid) with flexible diaphragm (in this case a sheet of rubber). Assuming that this is a closed ...
0
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1answer
213 views

Question on communication between universes in a level 1 multiverse

Can matter, energy, or information travel from one universe to another in a Level I Multiverse? That is, is there any communication between Hubble volumes in an eternal inflation-induced multiverse?
3
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1answer
301 views

Energy of an EM wave compared to energy of a photon

Several posts on this forum ask the question about the role of amplitude in calculating the energy of an Em wave. This struck me as odd since I learned that E=hv. There is no amplitude in the Planck ...
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1answer
455 views

Does the particle vibrate in 3D space? [closed]

As far as I know, particles vibrate with a frequency and wavelength determined by their energy level. Is this vibration in 3D space?
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2answers
121 views

Do all impacts create a wave-like disturbance in the medium through which they travel?

There is a scene in the first Matrix movie, where a helicopter strikes a skyscraper. The most interesting part is the 'slow-motion' bit where, as the helicopter strikes the building, a wave first ...
3
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2answers
744 views

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 ...