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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 the GPE of an object always equal the work done?

I had a question that said, "If you do 100 J of work to lift an object over your head, what is the gravitational potential energy relative to its starting position? What would be its gravitational ...
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3answers
58 views

Does potential energy get transferred from my body to a wall when I push a wall and fail to move it?

When I push a rock (and fail to move it), I do not do any work and therefore there should be no energy transfer. But my teacher says that, when one pushes a rock, energy is transferred to the rock ...
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3answers
178 views

What's the point of momentum? [closed]

I know this may sound like a strange question but I have always wondered what exactly the mathematical point of momentum is. I have understood energy to be an attempt to reformulate Newton's 2nd law ...
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1answer
33 views

Total energy, total momentum of two different balls [closed]

I have a ball out of plasticine thrown horizontally with speed $v$ on a steel ball that is attached from top to the ground on flexible straps in the middle (see picture). The mass of plasticine is $m$,...
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2answers
81 views

Electrons Getting mass from energy

According to relation $E=mc^2$ energy and mass are equivalent. So, when an electron in its orbit gets energy from out, does its mass increase? If not, where is the energy stored? I am not ...
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2answers
47 views

Calculating initial average energy of a thermal state

We are given a system with the Hamiltionian $$H = \sum_i \omega_i a^{\dagger}_ia_i \tag{1}$$ where $a^{\dagger}_i, a_i$ are creation and anihilation operators. I did the calculations and got the ...
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1answer
14 views

Can fire create pressure if it released it energy as fast as an explosion [closed]

Since fire release energy, I wanna know if it can create a shockwave if it release it energy as fast as an explosion
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1answer
29 views

Energy recovery from refinery cooling tower

Is there any possibility of recovering exhaust energy from a cooling tower by putting a wind turbine above it? Would this affect the performance of the cooling tower?
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4answers
134 views

Why do we use heat engines if they are so inefficient?

Let's say I wish to build an engine which will launch a box vertically upwards. I propose two such engine designs: Engine 1 (finger, spring, box) Step 1: Orient uncompressed spring vertically. ...
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2answers
110 views

Conceptual understanding of Schrödinger equation

So I followed this lecture: https://www.youtube.com/watch?v=qu-jyrwW6hw which starts of with the statement: If you have a Schrödinger equation for an energy eigenstate you have $$-\frac{\hbar}{2m}...
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0answers
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Magnitude of mass polarization

When solving many-body atomic Hamiltonians, (such as Helium), there exists a term in the Hamiltonian which looks something like: $$ \begin{equation} \frac{1}{M}\vec{\nabla}_i\cdot\vec{\nabla}_j \end{...
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1answer
202 views

To what extent is the heat in the focal point due to visible light?

When focusing sunlight on a piece of paper, e.g. with magnifying glass, the paper will be charred and might eventually even burn (assuming low cloudiness). To what extent is the heat a result of the ...
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170 views

How is a capacitor implemented in Kirchoff's Loop Rule?

I'm real stumped here. I may be missing something, but I'm genuinely perplexed as to how one would add a capacitor to the list of elements being added to an equation through Kirchoff's Loop Rule (KVL)...
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1answer
139 views

Number density of photons and the total energy of the universe

I was reading over some assignment solutions that my lecturer put up and one of them said that instead of calculating the number of photons in the universe with the familiar method of $$\int^{\infty}...
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1answer
59 views

How to analyse the LHC signal for Higgs?

With increasing energy the collision decreases in the plot for signal in LHC. why is that? and at an energy 125GeV the no of events suddenly increases. How this proves that higgs has a mass of 125GeV?
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3answers
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water pipes break when temperature goes down, how to estimate the energy involved?

Normally low temperature is associated with lower energy state and high temperature with higher energy state. There is an apparent paradox when a water pipe breaks due to low temperature: when ...
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2answers
52 views

I am having trouble understanding work and the factor of time

Consider this: 1 kg object vs 1000 kg object No friction applies in my example and the machine I am using is 100% efficient. Some machine using a fuel applies 1 N of force over 1 meter to each object ...
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13answers
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If visible light has more energy than microwaves, why isn't visible light dangerous?

Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all ...
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2answers
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In a masses inelastic collision, K energy convert to heat but velocity remain same. we receive heat without losing velocity? how?

I have read the answer about the energy and momentum conservation question but I have a great question now! Imagine we have two masses which one of them is at rest and another move and collide to the ...
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0answers
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Free energy of non-interacting bosons in mean field

The result As a mathematician I am currently struggling to understand Tóth's Phase transition in an interacting Bose system. An application of the theory of Ventsel' and Freidlin. The free energy (...
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0answers
21 views

Does Oberth Effect work in free space or it works only in gravitational field (gravitational well)?

From Wikipedia article about Oberth Effect it is not clear if it works in free space (no gravity, no air, etc). For example, in very far space between 2 galaxies, gravity is almost zero. There are 2 ...
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1answer
30 views

Does a field gain energy or does the mass/charge?

My textbook reads that when a mass/ charge is moved into the influence of a gravitational/ electric field the field gains/ loses energy rather than the mass/ charge. How can this be explained?
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0answers
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What happens to energy when waves cancel out? [duplicate]

So this is basically What happens to the energy when waves perfectly cancel each other? again, but I'm not understanding the answers given (or they don't address what I am confused about) Basically ...
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1answer
46 views

How do salt crystals evaporate in water?

Salt dissolves in water but when water has evaporated it is still there. What has happened to the salt in the water and why is it still there when water has evaporated?
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1answer
56 views

Population of conformers in $NVT$ ensemble

I have one question - I've done simulations using Car Parrinello Molecular Dynamics together with Thermodynamic Integration method (liquid phase), hence I have calculated Helmholtz energies for my ...
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0answers
24 views

Does the energy of two entangled quanta vary with distance?

my question is about,Does the energy of two entangled quanta vary with distance?
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1answer
62 views

Is There a Limit to The Energy-density Confined to a Black-hole Structure, Consisting of a Schwarzschild Sphere? [closed]

Imagine two particles repeatedly colliding with increasing momentum,like a dense collection of particles confined within the envelope of a collapsing star that's close to becoming a black hole. Is ...
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1answer
72 views

Energy spacetime warping

If energy warps spacetime, then does light warp spacetime? And if special relativity says that things near the speed of light increase in relativistic mass, then does light have a relativistic mass? ...
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2answers
59 views

What is the energy of an atomic orbital?

When we refer to energy of an atomic orbital what is this energy ? is potential energy ? but if is potential energy then shouldn't be considered the whole potential energy of the atom ( potential ...
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1answer
81 views

Irreversible and reversible compression work

Why is work done on the gas when it is compressed from (p2,V2) (pressure,volume) to (p1,V1) against constant pressure external pressure p1 maximum when it is done irreversibly? In reversible process, ...
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1answer
36 views

Formula for Power from Kinetic Energy

Work Done = $Fd$ Power = $Fv$ If the (net) Work Done = Change in Kinetic Energy, and the object starts from rest: Work Done = $\frac{1}{2} mv^2$ Power = $\frac{1}{2} m av$ Power = $\frac{1}{2} ...
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3answers
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Photon energy comes in packets

From the HyperPhysics page on the Photoelectric Effect: According to the Planck hypothesis, all electromagnetic radiation is quantized and occurs in finite "bundles" of energy which we call photons....
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2answers
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Constant gravitational acceleration $g$ and energy

I've been taught that $g$ is constant for different masses and that if I were to drop a heavy object and a light object from the same height then they would reach the ground at the same instant with ...
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Generic Differential Equation for Oberth Effect

In Wikipedia article about Oberth Effect there is an example of calculation in a simple case when the differential equation is not required. In non-English versions of this article (for example, ...
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3answers
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How are various forms of energy ability to do work? [closed]

According to various sources that i have come across, energy is the ability to do work. Can someone elaborate how diff forms of energy like potential energy and kinetic energy are ability to do work? ...
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4answers
92 views

$E=hf$ true for all implies $E=pv$ true for all?

In the answer to this question: Can I apply $E=hf$ to a particle having mass? It was stated that $E=hf$ is true for all particles. If so, doesn't this imply that $E=$momentum x velocity is true for ...
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1answer
75 views

Work done in accelerating an object in circular motion

In a hammer throw competition, an athlete spins a “hammer” before releasing it. The “hammer” used in this sport is a metal ball of mass 𝑀 = 8 kg and diameter 𝐷 = 30cm, which is attached to a ...
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1answer
28 views

How to estimate energy of piezo igniter discharge?

Question for fun. We all know piezo igniters, these small friends, like following one: All of them are probably quite similar: same spring, same piezo, same hit force, and so on. Also I have some ...
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3answers
75 views

Does the wave function carry energy and momenta?

I was reading a forum regarding the reality of the wave function, and one user (who apparently works in quantum foundations) stated that "the wavefunction carries no energy or momenta and this ...
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0answers
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Is this solution in Conquering the Physics GRE incorrect? [closed]

In Conquering the Physics GRE 2nd edition, Exam 3 problem 20, the statement is as follows: A metal bar is pulled at constant velocity $v\mathbf{\hat{x}}$ along two metal rails a distance $d$ apart ...
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1answer
47 views

Cycling: The energy behind it

I'm developing a school project (I'm studying software engineering) and it's about a sharing bicycles company. We need to calculate the total amount of necessary energy to travel from one point to ...
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3answers
99 views

How can we define energy other than the definition that it's a capability to do work? [closed]

It is actually a property of energy that it can do some work not an actual mean to define it because we cannot define a thing on the basis of what it is doing or what it can do.
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4answers
201 views

Electron in free space and Schrodinger's equation

Topic: Quantum Theory of Solids I have come across the following text: Electron in Free Space: Consider the motion of an electron in free space. If there is no force acting on the particle, ...
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1answer
51 views

Joule expansion and center of mass

This question comes from a doubt resulting from some physics forums. Similar to and related to this question, I have a doubt on Joule expansion raised by reading too much bad faith arguments. I'm not ...
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2answers
38 views

What's the total energy when I tie a mass with a string and then rotate it in a radius $r$ with angular velocity $\omega$?

I know it may be a very silly question. But when we are calculating the total energy, shouldn't we also consider the potential energy due to the centrifugal force acting on the body? Or as, we are ...
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2answers
51 views

Is it possible to add energy to an antiparticle?

The title says most of it but the more drawn out version is. If you were to add energy to a single particle or antiparticle in a pair, what would be the effects, if it is possible to do.
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1answer
36 views

Why Gibbs energy for nucleation theory?

In nucleation theory, the free energy is given by (https://en.wikipedia.org/wiki/Classical_nucleation_theory but in many other places also): $$\Delta G=\frac{4\pi }{3}r^3\Delta g +4\pi r^2\sigma,$$ ...
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1answer
96 views

Whether this proof regarding Bohr's second postulate is true or false?

Let us assume a particle oscillating with displacement $x$. Now $x = A\sin(2πft)$ $$\frac{\mathrm d x}{\mathrm dt} = v = 2πfA\cos(2πft)$$ Now $KE_\text{max}$ can be given when cosine value is 1; ...
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2answers
86 views

Inconsistent Results with Momentum and Kinetic Energy

A speed skater with a mass of $m_1$ kg is moving at $v_{1i}$ m/s. He prepares to push the next speed skater of mass $m_2$ kg moving at $v_{2i}$ m/s. After the push, the velocity of the first skater ...
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2answers
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Proof for $W_{\text{total}}$

Looking upon a certain solution of a problem in Griffiths regarding the work done in arranging two concentric spheres with inner shell having charge $q$ and outer shell with charge $-q$ and I found a ...