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 the [energy-conservation] tag if it is specifically about its conservation.
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Cryogenic coolers [closed]
Could someone explain to me in very high detail exactly how cryogenic coolers work. Also, if the whole system is under a vacuum, how can the compressor work? Please, do include images, since that ...
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Gravitational collapse - proof that energy dissipation is required?
As an undergraduate, I took a short course on astrophysics, where I encountered the Jeans mass. This is the critical mass for a spherical cloud of interstellar gas above which the cloud is predicted ...
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Why do objects slow down when they hit the ground? [closed]
Say you drop an object on the ground. For the purpose of this question, I am just focusing on the slowing down of the object, not if it rebounds. I was just wondering which of the two reasons explains ...
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Understand power rating in layman terms
I have recently started the chapter of electricity of class 8. I am not understanding the concept of power rating of appliances. When we say that a bulb is rated 220V-100W, which means, according to ...
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Does this double well potential contradict the fact that there is no degeneracy for one-dimensional bound states?
This example is taken from Modern Quantum Mechanics by Sakurai.
Consider a symmetric double well potential in one-dimension with a barrier of height $V_0$ and width $a$ at the middle. The eigenstates ...
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Strange calculus involved in work and power [closed]
If force is given by $$F(t)= 3t^2i + t^3j$$ and velocity is $$v(t)= 5t^2i + 2tj$$ then what is work done in time $t$. Now we can obtain power by their dot product $F.v$ and then integrate power to get ...
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Gibbs Free Energy and Definitions of Entropy [duplicate]
When we speak about entropy, it's classically defined as
$\delta S = \frac {\delta Q}{T}$
Where, I emphasize that it's the definition for only a change in entropy and not entropy itself (That's how I ...
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Total differential of internal energy $U$ in terms of $p$ and $T$ using first law of thermodynamics in Fermi's Thermodynamics
While reading pages 19-20 of Enrico Fermi's classic introductory text on Thermodynamics, I ran into two sources of confusion with his application of the First Law. Fermi introduces a peculiar notation ...
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Expressing internal energy of a system in thermodynamics
Recently I came across a article where it was written that
1.$\Delta U= nC_v\Delta T$ for all thermodynamic process
2.but $\Delta U =nC_p\Delta T$ is true only in a isobaric process
How true are the ...
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Could cosmic rays induce a vacuum decay in the future?
I've been told that very energetic cosmic rays could cause a vacuum phase transition or vacuum decay (and even could cause a true vacuum level to go "uphill" to a false vacuum) due to their ...
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Why the work done by surrounding on the piston is same as average work done by surrounding on the gas inside the cylinder? [closed]
In thermodynamics when we derive the formula for work done by the surrounding on the gas, we actually derive the formula for work done by the surrounding on the piston and say that let the surrounding ...
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Where am I wrong in proving that force perpendicular to motion increases speed and kinetic energy? [closed]
Lets think of a helicopter flying at some height $h$. It throws a food packet to a person on the ground from air. Let's neglect the air drag.
The food packet is thrown only with some velocity $v_x$ in ...
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If a slice of a 4 dimensional metric violates an energy condition, does the 4 dim metric violate it aswell?
I 'm currently studying analogue gravity see this paper for a review. Here a 2+1 dimensional metric is derived:
$$
ds^2 = -dt^2 + (dr - \frac{A}{r} dt)^2 + (r d\theta - \frac{B}{r} dt)^2
$$
Now it ...
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Simulation of a battery with lifting up and role of salt bridge
Usually for explanation of the mechanism of a battery, it is modelled by lifting a mass from lower to higher position.
The attached figure shows a mass that goes down due to the gravitational ...
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How is the expression for work in this problem derived?
In this solution to the problem I found, the work expression comes out to be the force times $d$, the difference in distances from the collar to the force origin at positions A an B. I can't for the ...
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