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

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Why does kinetic energy below molecule bond energy break bonds?

I was thinking about why bullet can break molecular bonds when it hits solid target despite the fact that the kinetic energy of the individual atoms that make up the bullet is less that the molecule ...
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Why is my solar panel more efficient as the temperature increases, rather than less efficient?

I have recently performed an experiment in which I placed a solar panel inside a closed box, together with a heater and a lamp (60W). I increased the temperature using a heater from 20ºC to 50ºC. The ...
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How do electrons lose their kinetic energy in ideal wire?

Electrons keep accelerating due to the electric field (produced by the battery) along the circuit. So electrons gain kinetic energy, hence their drift velocity changes. But this is not the case: ...
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What does this mean? World consume 14 trillion watts of power

I am not very clear about this statement. Does that mean in every second we are consuming that much energy?
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Why is there energy being spent / work being done in a static system?

Sorry that I don't have pictures. Imagine I have a steel circle, like a hula hoop. On opposite sides of that circle I attach two springs, then stretch them. They meet in center where I hook them ...
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In special relativity is mass just a measure of all other energy than kinetic?

The energy momentum equation in special relativity is: $$E^2=(pc)^2+(mc^2)^2.$$ and it holds for a moving but not accelerating object. One special case is the massless photon: $$E=pc.$$ And another ...
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How much energy does it take to form a plasma channel with a laser?

The usage is for something like this https://en.wikipedia.org/wiki/Electrolaser I know that the laser is powered for an instant in which a plasma channel is formed for the electricity to flow through,...
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Quantization of angular momentum of system of particles

Suppose there is a system of particles interacting with each other. Is it the angular momentum of each particles which would be quantized as $\sqrt{n(n+1)} \hbar$ or is the angular momentum of the ...
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Proper definition of Internal energy

In Internal energy of a gas ($U$), we have to include ALL types of energies possible like $KE$, bond energies, nuclear interaction energies, etc.., However we have derived that $U = (f/2)nRT$ from ...
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Is this dark energy? [on hold]

Consider a particle travelling near the speed of light towards a planet- relativity states that the space according to the particle shrinks between the particle and the planet as the particle ...
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How much energy would it take to blow up the Earth?

There is a common statement running around that we as a species has enough nuclear weapons to blow up the earth several times over. What I want to know is: by how many orders of magnitude is that a ...
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Energy consumption from acceleration

I have an interesting problem. I have a machine which has to lift 35 kg (this is the total mass of the object and the lifting arm). The lifting is done by a servo motor. Now I want to calculate the ...
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Entropy change of the surroundings

My textbook says: $\displaystyle\Delta S_{surr}=\frac{q_{surr}}{T}=-\frac{q_{sys}}{T}$ So far, so good. It then goes to say: $\displaystyle\Delta S_{surr}=\frac{-\Delta H_{sys}}{T}$ [at constant $P$...
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Varying of momentum for constant kinetic energy

How is that If the momentum of the particle is constant with time, its kinetic energy ($E_k$) should also be constant with time a true statement but the converse is false... When momentum is ...
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Energy contributions of Hamiltonian density

In Lancaster and Blundell, Quantum Field Theory for the Gifted Amateur, p.99, Hamiltonian density is \mathcal{H}=\frac{1}{2}[\partial_0\phi(x)]^2+\frac{1}{2}[\nabla\phi(x)]^2+\frac{...
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Why does kinetic energy increase quadratically, not linearly, with speed?

As Wikipedia says: [...] the kinetic energy of a non-rotating object of mass $m$ traveling at a speed $v$ is $\frac{1}{2}mv^2$. Why does this not increase linearly with speed? Why does it take so ...
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How would the angular velocity of the rod change if it slipped on the table?

I wanted to consider a second case of my homework assignment. We were asked to solve the question: A uniform rod of length b stands vertically upright on a horizontal plane in a position of unstable ...
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Difference between coherent and incoherent energy transfer (e.g. in photosynthesis)?

Several authors distinguish between incoherent and coherent when describing the energy transfer mechanism that forms the basis for photosynthesis. (e.g. Clegg & Sener 2010 and Keren & Paltiel ...
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Derivation of the K.E. formula without the work-energy theorem (or proof of the work-energy theorem without the kinetic energy formula)

All of the derivations I have seen for the kinetic energy formula have relied on the fact that work is the change in kinetic energy, something like the one found here: How to prove equation of kinetic ...
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If the heat capacity of an object changes does the internal energy or temperature of the object change?

Consider a spherical particle of material B contained in a spherical shell of material A. The thermal expansion coefficient of B is greater than that of A so that when the object is heated an internal ...
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Car Max Range Equation

In space engineering, thanks to the rocket equation, if you know some properties about a rocket (payload, fuel mass and specific impulse) you can compute the theoretical maximum distance the rocket ...
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charged plasma and ion grid in interaction in ion thrusters

I was just wondering ..... In this Image of an ion thruster, when the positively charged particles pass through the grids, wouldn't they just bombard the negatively charged grid(a fraction of them). ...
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Reduce temperature of fluid inside an isolated system without dissipating heat

Suppose you have a perfectly isolated system filled with a fluid, which cannot transfer heat nor matter to the external environment. Suppose you want to reduce the temperature of the fluid within ...
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Best way to apply force to all sides of a cylinder [on hold]

Im looking to apply force to all sides of a Cylinder from the inside with as much force possible without eruption.
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Stationary State of Quantum Mechanics [duplicate]

Why for every normalized solution to the time-independent Schrödinger equation $E$ must exceed the minimum value of $V(x)$?
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COSMIC ACCELERATION

Please forgive a probably naïve question from a lay person. I understand that galaxies are all moving away from us in every direction we look. And for any given distance the speed is the same. And ...
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Energy loss caused by a negative work

Let's supposed a box is sliding on a friction-less surface, so it has some KE at this point, and let's imagine an external force is being applied on the opposite direction of the displacement of the ...
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The strict definition of partition function in continuous system

I am confused about the definition of the partition function. From the class of statistical thermodynamics, I've learned that the partition function for a system with continuous energy can be ...
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How does conservation of energy work?

I understand that the law of conservation of energy states that energy cannot be created or destroyed, it can only change from one form to another. This means that the total energy before a certain ...
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Instantly freeza lava [closed]

If you could magically freeze lava, what would be the temperature and energy output of your spell (in KJ/Tons)? In this case the lava is 20 meters in diameters and instantly spawned beneath your feet.
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Using Helmholtz Free Energy to Calculate Liquid Density

My objective is to find an equation of state (EoS) for density, i.e. density as a function of pressure, temperature and concentration, for aqueous acids, bases and salts. A StackExchange user ...
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Energy of a light wave

I know that the energy of a photon can just be found from the equation E = hv. However, if we measure light as a wave, can the energy be found from the amplitude rather than the frequency, like you ...
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What is beyond Gamma Rays and Radiowaves in the Electromagnetic Spectrum?

The electromagnetic spectrum is commonly refered to as consisting of; Radio-waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays - of increasing frequency from left to right. ...
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What does the Higgs boson have to do with the uncertainty principle and quantum oscillations?

I was looking in New Scientist the other day when I saw something to do with the Higgs boson, energy levels, entropy, space/time, quantum oscillations and many other things. It was in a feature to do ...