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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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55 views

Convert emotion into energy? [on hold]

if it were possible to quantify emotion, would it be possible, theoretically, to then convert it into usable energy?
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1answer
91 views

Energy stored in system or field?

I am having difficulty in understanding whether fields store momentum and energy or particles store them or both fields and particles store them? System of potential energy In the above source it ...
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3answers
45 views

Energy extraction from the layers of sea water?

Could it be possible/reasonable to extract Peltier thermoelectric energy by using a long rod of suitable material that connects the cold bottom of the ocean and the warm surface layer?
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22 views

Can non-conservative field store energy when work is done?

Taking a non-conservative field like magnetic field (in presence of current density), when work is done can it store energy? If so how?
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1answer
63 views

A doubt regarding Planck's quantum theory [duplicate]

I am a beginner and I have a problem regarding Planck's Quantum Theory The following is one of the postulate of Planck's Quantum Theory 1) The energy of each quantum is directly proportional to ...
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0answers
33 views
+50

Does freezing point depression also affect the speed at which something melts?

If you have a pure water frozen, then it should begin to melt if you apply 33°F air to it. If you have impure water that's frozen, it's melting temperature might have dropped to 30°F. If you apply ...
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0answers
16 views

Can you predict how much fuel you need to launch a rocket based on conservation of energy?

I was just wondering if there was a way to calculate how much fuel you need for launch, possibly to do with chemical energy to kinetic energy. Thanks
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0answers
44 views

Are conservation of mass and conservation of energy *independent* constraints for physical systems?

I'm modeling fluid systems and want to use conservation of mass (aka 'continuity') and conservation of energy as constraints to help solve for certain system parameters. But it occurred to me that the ...
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1answer
63 views

Why is it easier to ride a bicycle than to run? [duplicate]

While it is very hard and energy-consuming to run a marathon, covering the same distance by bike is doable by most people. Where exactly does the gain come from? Assuming for simplicity that we are ...
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0answers
51 views

A particle of mass $M$ decays into two particles of mass $m_{1}$ and $m_{2}$ [closed]

I can't understand how to get what the problems asks for: A particle of mass M decays into two particles of mass $m_{1}$ and $m_{2}$. A detector measures your energies and moments like this: $$E_{1} =...
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0answers
31 views

Why does the vacuum in the real world not have infinite negative charge density? [on hold]

Physical vacuum can only be stable if all the negative energy states available to electrons are occupied. If this is so then vacuum state would have infinite negative charge density. This blatantly ...
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1answer
83 views

Kinetic energy always time independent?! Where is my mistake? [closed]

I have some problems understanding the Lagrangian and the Hamiltonian formalism. Those can be condensed in the following "derivation" of $\frac{\partial T}{\partial t} = 0$ from the equation $\frac{\...
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1answer
22 views

Confusion on kinetic energy quadratic forms and eigenfrequencies

I am new to the idea of expressing kinetic energy in terms of the quadratic form. I noticed that online, people often express the kinetic energy as: $$T = \frac{1}{2} \dot q^T M \dot q \tag{1}$$ ...
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1answer
65 views

Mass required to accelerate to relativistic speed

What would the rest mass of a rocket need to be if it carries a payload of 1kg and is accelerated to 1/2 c and then decelerated to a stop. Assume: 1 - energy required is obtained via fusion of ...
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2answers
58 views

A spacecraft orbiting the sun charges a battery which becomes a tiny bit more massive. How does this effect the velocity of the spacecraft

According to E=mc² the spacecraft which stores the Energy from the sun becomes a tiny bit more massive. how does this effect the impulse of this spacecraft. Would it grow because P = (m + extra mass) *...
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2answers
95 views

In the tunnel through the Earth thought experiment, how does total energy of a particle vary when it goes from surface of the Earth to its center?

In the typical tunnel through the center of the Earth thought experiment, a particle at the surface would oscillate between the two diametrically opposite points ignoring the rotation of the Earth. ...
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1answer
34 views

Energy consumption [closed]

If the yearly worldwide energy consumption is 80,000 TWh, and a particular earthquake generates 1.6x10^13 Joules of energy. If we could harness all of the energy from the earthquake, for how long ...
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1answer
58 views

Projectile coming to a full stop at impact versus breaking through and continuing on

In the following scenario neglect any deformation forces within materials and assume the collision is inelastic. There are no instances of rebounding of the projectile at impact. There is no flying ...
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4answers
104 views

Does energy exist or is it just a relationship between other fundamental things?

Could anyone tell me what energy really is?I searched for it and some people said that energy doesn't exist physically and it is not fundamental but it is a relationship between other fundamental ...
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2answers
34 views

Why is the entropy production inside the system zero for a reversible process?

For a reversible process, why is the production of entropy within the system equal to zero?
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2answers
47 views

What is the relativistic energy of a bounded static particle?

Premise: The speed of light is set $c = 1$. Let's consider an electron in an external electromagnetic field. Its four-momentum will be $$p^{\mu} = (E, \bar p) = (\gamma m_e, \gamma m_e \bar v),$$ ...
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2answers
64 views

What happens when amplitude of light increases?

As $E=hf$ and $\mathrm{amplitude}^2 = \mathrm{energy}$ of an EM wave, if I increase the amplitude does that then affect wavelength and frequency to keep $c$ constant? I assume so since high energy ...
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2answers
135 views

Do calculations require energy?

A typical computer takes some energy "from the wall" while operating. I know that energy is spent on: Heating various components (psu/vrm/cpu/ram/ssd, so on) Fan/air motion to remove that heat (also ...
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1answer
27 views

How can internal energy be expressed as a function of any two of $p, v, T$?

In the book of Irey, Theormodynamics, the author states that (while talking about single phase substances) For a simple compressible media, we may choose our measurable independent variables any ...
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3answers
369 views

Whats the next step after commercial fusion reactors? [closed]

I'm trying to write some science fiction where they've had nuclear fusion working for quite sometime, interplanetary travel is no problem, and they're debating making the next step to a radical new, ...
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2answers
127 views

A hypothesis based on the principle of conservation of momentum

When a ball hits a wall (ground), some quantity of its momentum must be transferred to the wall at rest. If else the ball would bounce back with the exact same speed as it did when it collided with ...
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3answers
59 views

Kinetic energy of an object

We know that motion is relative. So let an object(o) be moving with a certain velocity with respect to an object (A).If another object (B) is moving with respect to (A) at a given moment and they ...
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2answers
168 views

Value of $\beta$ in Boltzmann statistics when degeneracy of quantum states is taken into account

The relationship between entropy $S$, the total number of particles $N$, the total energy $U(\beta)$, the partition function $Z(\beta)$ and a yet to be defined constant $\beta$ is: $$S(\beta)=k_BN \...
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0answers
54 views

I don't understand how does the Conservation of Energy Law apply to a Negative Unity Power Factor?

How can this be a Law if the total watts of an electrical circuit can vary per unit of time? In other words, isn't it possible to break down this so-called inviolate Law into at least two constituent ...
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0answers
24 views

Elastic collision

In an elastic collision, 2 processes can be said to take place as mentioned here in the accepted answer: Why does a billiard ball stop when it hits another billiard ball head on? First by the ...
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0answers
14 views

Do delocalized electrons have different energies?

Consider a molecule with alternating single and double bonds between carbon atoms, such that multiple resonant configurations are possible, e.g. beta-carotene. While using UToko's edx course about ...
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1answer
21 views

Polar form of Newton's Second Law

Can someone please show the steps for deriving the total energy of a particle from the Polar form of Newton's Second Law?
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1answer
42 views

Contradiction between conservation of momentum and conservation of energy [closed]

Let's say that a $2\text{ kg}$ cart is rolling (frictionless) along a surface at $2\text{ ms}^{-1}$. A suspended $2\text{ kg}$ weight is then dropped onto it from above. If we apply the law of ...
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1answer
32 views

Work-Kinetic energy theorem derivation

So I came across this derivation in the book Classical Mechanics by Herbert Goldstein. I don't follow from the second step onwards. I understand that there's a dot product, but how do you compute it? ...
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1answer
41 views

KE in photoelectric effect

I photoelectric effect when a single photon's energy is absorbed, why don't all get the same Max $KE$. Because for an electron, there can be no loss in heat or any friction and all. Why do most of the ...
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1answer
26 views

Clarification on temperature's relationship to container volume

My physics textbook says that if a container that contains some amount of gas is expanded then the temperature of the gas will decrease But isn't this only if the container is increased in volume ...
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1answer
24 views

Interpretation of change in entropy and how to formulate an expression for how much energy required to mix gases.?

From statistical mechanics one cab derive the change of entropy of the mixing of two ideal gases with the result $$\Delta S_\text{mix} = - n R \Sigma_{i} x_i \ln(x_i)$$ where $n$ is the total amount ...
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2answers
62 views

Why expression of energy occurs in triplet?

I have basically two questions in mind,which are Why expression of energy occurs in triplet? Why the expressions are somewhat symmetrical? Coming to elaborated form of 1st part, we have $$U=\frac{...
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0answers
29 views

Why is photon quantized in vacuum? [duplicate]

Apparition of quantized energy levels in quantum physics is usually explained in analogy with sound waves in a box (like in music instruments): the wave has to satisfy the boundary conditions and ...
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1answer
30 views

Vibrations in Stones and Crystals [closed]

I have read studies done that indicate certain sounds can either disrupt or reinforce the molecular structure (I think this is the terminology used) of living organisms. This is based on the idea that ...
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3answers
76 views

$\Delta K=\Delta U$ vs $\Delta K = -\Delta U$

While doing physics homework, I noticed that in some problems, the change in kinetic energy(KE) is equal to the change in potential energy(PE), even though I learned that conservation of energy shows ...
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2answers
98 views

Physical concept of imaginary energy [closed]

I want to know that what's the physical description of complex energy? The energies have the real and imaginary parts.
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1answer
59 views

Oscillation of 2 identical pendulums connected by a rubber band

While solving A level past papers, I came across the following question. For reference, this is the Edexcel GCE A2 Physics Paper 2 from June 2018. What does not make sense in my mind is the fact that ...
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2answers
50 views

How do we extract energy from capacitors?

I have an intuitive reasoning for the use of capacitors. I think that it is used to store electrical energy. Without going in much detail in engineering and being at an introductory level of ...
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2answers
89 views

Which is positive? which is negative? about laws thermodynamics…from problem solve

1) A hot block of iron does 50 kJ of work on a cold floor. The block of iron also transfers 20 kJ of heat energy to the air. Calculate the change in energy (in kJ) of the iron block. 2) A chef ...
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1answer
129 views

Need verification if this simple derivation of the Schrödinger equation is valid

By 1924 it was well observed that matter (as well as light) has wave-particle duality (later named quantum), and the wavelength-momentum-energy relation of quanta $$\lambda=\frac{h}{p}\;\;\...
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1answer
49 views

Effects of measurement on particle energy

According to quantum mechanics, once you measure a particle's energy, its wave function collapse into some state, an eigenfunction with some eigenvalue (which is the particle energy). But if a ...
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1answer
36 views

Statistical mechanics Calculating sums [closed]

The energy is given by: $$ E(\sigma) = -\sum_{i=1}^{N}\sigma_i + a \sum_{i=1}^{N}\sigma_i^2 $$ where $a$ is constant. I have to calculate the following: $$\left\langle \frac{1}{N}\sum_{i=1}^{N}\...
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5answers
1k views

Is ideal gas incompressible?

If so, I have read that for $C_P$ and $C_V$ for an incompressible gas are identical (in Heat Transfer by Yunus A. Cengel). Then how will the relation between $C_P$ and $C_V$ ($C_P-C_V=R$) hold for an ...
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1answer
35 views

Difference between expected $p_0$-value and observed $p_0$-value?

In the ATLAS paper for the higgs discovery, they used 2 kinds of different $p_0$-values. One is the expected $p_0$-value, the other one is observed $p_0$-value. What's the difference between the ...