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Questions tagged [dissipation]

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Validity of $\mbox{d}H/\mbox{d}t=\partial H/\partial t$ for dissipative systems [closed]

It' well known that in Hamiltonian formalism one has $$ \frac{\mbox{d}H}{\mbox{d}t} = \frac{\partial H}{\partial t}.\tag{*} $$ One proof can be found here. Therefore, the total change of energy during ...
Luessiaw's user avatar
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1 answer
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Can an optical medium be lossless and dispersive?

Occasionally, I come across the phrase "lossless dispersive linear optical medium". How can such a medium be possible mathematically? I mean the real and imaginary parts of the electric ...
apadana's user avatar
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4 votes
1 answer
163 views

Would the Moon move away if the Earth were frozen with no liquid tide?

The moon is moving further from the Earth. To the extent that after 600 million years we will no longer enjoy full solar eclipses as it will be too far away to completely block the sun. The reason the ...
Francis Cagney's user avatar
1 vote
0 answers
22 views

Output of ventilator and air friction

Imagine you have a ventilator with straight rectangular ventilator blades which are rotated at some small angle from a perpendicular line to the rotating axis. The ventilator has 100% efficiency (all ...
Emma m's user avatar
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1 vote
2 answers
40 views

Why exactly (on the level of particles interacting with each other) do things heat up with friction? E.g. airplane from friction with air

Why exactly (on the level of particles interacting with each other) do things heat up with friction? E.g. airplane from friction with air. Also what is the difference between conduction and convection,...
Alexei M's user avatar
0 votes
3 answers
89 views

Does a single ball undergoing ideal simple harmonic motion count as being in thermodynamic equilibrium?

(Posting this and deleting a previous similar post to make the question more clear.) Suppose we have an isolated system inside a box consisting of a spring and a ball attached to the spring. The ball ...
Maximal Ideal's user avatar
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0 answers
28 views

Damping of a Lagrangian System in 3D [duplicate]

I have a Lagrangian, that describes a Pendulum hanging on a spinning disk in 3D. It looks like this: $$ L(p,\lambda, t) = \frac 12m\|\dot p\|^2-m g p\cdot\hat k+\lambda(\|p-q\|^2-l^2) $$ with $p$ and $...
Mo711's user avatar
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2 votes
1 answer
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How to demonstrate in a simple way that this system of differential equations form a damped harmonic oscillator? [closed]

How may I demonstrate in the most simple way that the following system of differential equation form a damped harmonic oscillator ? $$ \dot x = -\alpha_x x - \omega y \\ \dot y = -\alpha_y y + \omega ...
chmike's user avatar
  • 123
3 votes
1 answer
119 views

Information Loss in Chaos Theory

Is it accurate to suggest that in chaos theory, information is in practice lost due to the impossibility of characterizing the system's state with infinite precision, making it unfeasible to run the ...
Omid's user avatar
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19 votes
3 answers
3k views

Rocket attached to a pendulum. How is energy conserved?

I'm trying to wrap my head around a conceptual problem involving a simple pendulum with a rocket attached to its mass. Imagine the rocket expels gas to provide a tangential thrust force. However, the ...
Eduardo González's user avatar
7 votes
2 answers
755 views

When the energy in a conductor is not carried by the electrons, how resistances warm up?

The energy flux in a conductor paints the picture that the "collisions" of the electrons with atoms (Drude Model) are not the reason for an resistance warming up in the presence of an ...
Niclas's user avatar
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0 answers
15 views

Rotating disc with viscous damping with large initial angle (always 90 degrees) (unbalance/instability)

I have an application for a rotating disc with inertia that is put on a "knife edge" balancing fixture. The disc is then released in order to find the "heavy spot", once identified ...
Mikro1234's user avatar
0 votes
2 answers
106 views

Where does a body get its energy to heat up when falling from height $h$?

When a body falls from a height $h$ it loses some energy to the surroundings, is it the energy that is lost to the surroundings that increases its temperature on the remaining energy that is stored in ...
Ritsu's user avatar
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0 answers
51 views

Energy loss due to Cherenkov radiation

I'm trying to find a formula for (or some sort of direction towards approximating) the energy lost by a ultra relativistic positron when traveling through a cherenkov detector but I can't seem to find ...
Aiden.6's user avatar
0 votes
2 answers
87 views

Heat as a path dependent integral

Heat can be considered as an inexact differential. Hence, we could conclude that: there exists a path $\gamma$,such that: $$ \oint\delta Q \ne 0 $$ Hence, $\int\delta Q\ne\Delta Q$. i.e. $\Delta Q$ ...
Aditya Krishna Panickar's user avatar
1 vote
1 answer
72 views

Direct conversion of potential energy into heat

Is it possible for potential energy to be dissipated (converted into heat) without being first converted into kinetic energy? Put differently, are there isolated systems at complete rest which turn ...
BlenderBender's user avatar
1 vote
2 answers
77 views

Accelerating car under the influence of rolling friction

Consider the following textbook problem: An electric car of mass $m = 3500 kg$ has stored $E = 100 kWh$ in its battery. The rolling resistance coefficient is $\mu_R = 0.8$. How far can the car travel ...
BlenderBender's user avatar
0 votes
5 answers
115 views

Energy and Non-conservative forces

I understand that one cannot assign a potential energy to all points in space in the presence of a non-conservative force field due to the work done by the force being dependent on the path taken. ...
Cognoscenti's user avatar
0 votes
1 answer
107 views

Where does the energy go in inelastic collisions?

Chabay and Sherwood write in Matter and Interactions on page 406 about sticking collisions: We'll consider an inelastic collision in which a truck and a car collide in an icy intersection and stick ...
Julia's user avatar
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-1 votes
2 answers
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What’s wrong with this idea for an energy generator? [closed]

Okay I know a perpetuum mobile is impossible, so I think this should be wrong. I thought about heat pumps with a COP of 3.5, which is like 350% efficiency compared to a simple electrical resistor. Now ...
user1009013's user avatar
1 vote
1 answer
62 views

Modeling a viscoelastic string with a collection of damped spring oscillators? (To replace finite difference model.) How to find $Q$ per harmonic?

Background I have simulated a vibrating viscoelastic string fixed at each end under tension using finite difference modeling. Most simply this can be done using Kelvin-Voigt style mass-spring dampers ...
mike's user avatar
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2 votes
0 answers
54 views

Vibrating string and damping

Suppose we have a string (in tension) with its ends fixed. Think of a guitar string. Suppose we start with a plucked initial position and we let the string free. If we use the wave equation: $u_{tt}=c^...
Plemath's user avatar
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1 vote
1 answer
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When does exponentially damping term in Lagrangian make physical sense

I have a question on adding dissipation into the Lagrangian. On this page: https://profoundphysics.com/friction-in-lagrangian-mechanics/ the approach with adding an exponential factor to the ...
user202542's user avatar
-1 votes
1 answer
37 views

Continuity Equation on a Non-Ideal System

I recently watched a video on the diffusion equation for neutrons in a fissile material, and at about 2:30 minutes into the video, the author points out that the right hand side of the continuity ...
liuzp's user avatar
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3 votes
1 answer
158 views

Infinite reflection inside a glass loop

If you had a loop made of completely transparent glass (or other material), in the shape of a donut; think atomic collider (but probably not needing to be so large :) ), and you introduced light from ...
Steve Knowles's user avatar
4 votes
1 answer
512 views

Sloshing water coming to rest?

Something I've noticed is that when I jostle a glass of water, the water inside will start sloshing back and forth. Gradually, the water comes to rest. However, if I move the glass (i.e., translate it)...
Duncan Ramage's user avatar
0 votes
0 answers
30 views

Asymmetry when $t\rightarrow -t$ [duplicate]

If we consider the equation of critical damping $$x=(a+bt)e^{-ct}$$ then the graph is However, it is asymmetric for positive and negative time values. I have an intuition that this should be the case ...
GedankenExperimentalist's user avatar
1 vote
3 answers
66 views

The lowering of a block using a spring and the net work done by each force involved

A spring hangs vertically in its relaxed state. A block of mass m is attached to the spring, but the block is held in place so that the spring at first does not stretch. Now the hand holding the block ...
Shiven Pradeep's user avatar
0 votes
0 answers
65 views

Solutions to critically damped harmonic oscillator?

From MITOpenCourseWare, I was learning about the damped harmonic oscillator. Some context is pasted below. Case (iii) Critical Damping (repeated real roots) If $b^2 = 4mk$ then the term under the ...
Arden Tsang's user avatar
-4 votes
1 answer
69 views

Could a perpetual motion machine be made using a filling buoyant object that sinks when filled and releases when bottoming out? [duplicate]

Could you make a perpetual motion machine via buoyancy? If you started with 2 types of fluids with different buoyancy. Then add a buoyant object capable of filling with the top fluid where it closes ...
Jans Mcclain's user avatar
-1 votes
1 answer
75 views

Can you generate more heat than the amount of work done? [closed]

I have doubt regarding how can COP of a refrigerator can be one! It can happen only when heat is more extracted when work inputed or rate of heat absorbed is more than power? Can any one of the reason ...
Tulasi Manikanta Nagala's user avatar
0 votes
3 answers
100 views

Perpetuum mobile working in vacuum

Can a perpetuum mobile work in a vacuum? I think when it is in vacuum it won’t stop working because of outside forces, because there is no outside forces. Tell me if I’m wrong.
GeorgeBg4273's user avatar
0 votes
1 answer
88 views

Energy dissipation derivation with friction in Lagrangian context

I am self-studying analytical mechanics, and I am stuck in an intermediate derivation of the equation for energy dissipation in a Lagrangian context. Frictional forces cannot be derived from any ...
user34909's user avatar
0 votes
4 answers
63 views

If there is a resistor there is a potential drop because the potential energy gets converted to other forms, then how can the current remain constant?

I am pretty confused about this. If a current flows through a resistor in a series circuit, the resistor opposes the flow of charges. Therefore, the total charge flowing per unit time decreases. How ...
Shrabasti Adhya's user avatar
0 votes
1 answer
25 views

Friction on a rolling body [duplicate]

I have been reading about rolling motion and I seem to have a confusion regarding the friction acting on such bodies. First off for a body to start rolling their has to be some friction b/w the ...
HexusXD's user avatar
1 vote
5 answers
455 views

If energy is conserved, why do we need to save energy?

The conservation of energy says that it can neither be created nor be destroyed, it can only be transferred from one form to another. i had this doubt in my mind for a long time that why do we need to ...
Rajiv Raj's user avatar
0 votes
0 answers
21 views

Fourier Transform of Damped Oscillations - Zero Frequency Peak and Shift [duplicate]

A damped oscillator has the time evolution: $$ y(t) = e^{-\Gamma t}\cos^2(\tilde{\omega}_0 t)$$ where $\Gamma$ is the damping rate, $\tilde{\omega}_0^2=\omega_0^2-\Gamma^2$ and $\omega_0$ is the ...
Angus's user avatar
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0 votes
0 answers
23 views

How to determine structure stiffness of a damped 1D system with acceleration - time graph?

Consider a damped system with only acceleration - time data is available, how to determine the structure stiffness (k)? Mass of the structure is also known. It moves in a horizontal direction, like a ...
Jimmy 's user avatar
1 vote
1 answer
250 views

Equations of motion for two masses connected by the Kelvin-Voigt Model

I have a system where two particles $x_1$ and $x_2$ in one dimension are connected by a spring and a dash in parallel. This is analogous to the Kelvin-Voigt model for viscoelastic materials. The two ...
jarhead's user avatar
  • 121
1 vote
0 answers
25 views

Relation between power dissipation and imag part of susceptibility [duplicate]

I am trying to understand the following relation between power dissipation and the imaginary part of the susceptibility, from Sethna's Statistical Mechanics textbook. Why does the integral equal the ...
photonica's user avatar
  • 101
1 vote
1 answer
113 views

Pushing a Hamiltonian part into dissipative part in Lindbladian

Suppose we have the following Lindbladian: $$\mathcal{L}(\rho) = -\frac{i}{\hbar}[H, \rho] + \sum_\alpha L_\alpha \rho L_\alpha^\dagger - \frac{1}{2}\{L_\alpha^\dagger L_\alpha, \rho \}.$$ Suppose we ...
userflux9674's user avatar
0 votes
3 answers
193 views

How does energy conversions happen in the circuit?

Let's imagine that we have battery connected to wire and the only component in circuit is light bulb and let's say we got 5V in battery. I'm looking for the intuitive explanation and not with the ...
Matt's user avatar
  • 367
1 vote
1 answer
128 views

Amplitude of a Damped Harmonic Oscillator

Background: What I know about simple harmonic oscillators For a simple (undamped) harmonic oscillator, one expression for the position as a function of time is $$ x(t) = x_0 \cos(\omega_0 t) + \frac{...
Bunji's user avatar
  • 1,302
1 vote
2 answers
315 views

Would sound get weaker in metal faster than in air over the same distance?

I'm finally closing some gaps in sound waves, so forgive me for lots of questions. In metal, it's said sound travels fastest. The reason is molecules are tightly packed(more dense) in metals than in ...
Giorgi's user avatar
  • 525
-1 votes
6 answers
530 views

Why sound gets weaker as it travels in air? [closed]

When we talk, our vibrating chords oscilate next air molecules which oscilate the next molecules and so on. Hence sound wave travels. As we know, energy that reaches the destination is not the same ...
Giorgi's user avatar
  • 525
0 votes
0 answers
44 views

Theory of conserved quantities in damped systems?

As is well-known, classical conserved systems have conserved quantities by virtue of continuous symmetries, which can be derived from Lagrangian mechanics. For example, two masses on a spring can swap ...
David's user avatar
  • 713
2 votes
1 answer
70 views

Why resistors consumes power? [duplicate]

this is a basic voltage divider circuit. Whenever electrons are about to enter in $R_2$ they have some energy. And when they leave R_2 their energy level decreases. what kind of energy we are talking ...
Sayan's user avatar
  • 131
1 vote
1 answer
319 views

Energy conservation in a forced spring-mass-damper, off of resonance

I understand that at resonance, a spring-mass-damper system will only require input energy from a forcing that matches the energy dissipated per cycle by the damper. Let's say that you have a system ...
Ethan 's user avatar
  • 11
3 votes
0 answers
49 views

Conserved quantities in overdamped dynamics

I have an implementation of over-damped Brownian dynamics, with particles that follow the version of the Newtons law where the inertia is absent. This is a common thing to do at micrometer scale. $m x'...
user13831679's user avatar
0 votes
0 answers
37 views

What is the relationship between quantum dissipative system and quantum impurity system?

Now I'm studying the phase transition of the many-body system as a school degree. What I'm curious that, I found the meaning of quantum impurity system is : One particle interacts with an ensemble ...
Sora S's user avatar
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