Questions tagged [dissipation]

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61
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6answers
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Why does a system try to minimize its total energy?

Why does a system like to minimize its total energy? For example, the total energy of a $H_2$ molecule is smaller than the that of two two isolated hydrogen atoms and that is why two $H$ atoms try to ...
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4answers
5k views

Will tsunami waves travel forever if there was no land?

If there was no land for tsunami waves to collide with, can the waves travel around the globe for forever?
16
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4answers
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Why can't we ascribe a (possibly velocity dependent) potential to a dissipative force?

Sorry if this is a silly question but I cant get my head around it.
16
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1answer
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Does fluid speed affect liquid cooling?

If you have a liquid-based cooling system, like the loop in the picture below, does the fluid speed actually matter? I can see how cycling the liquid too slowly would be bad, since the fluid would be ...
16
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3answers
690 views

Can we quantize Aristotelian physics?

Aristotelian physics, shorn of whatever the historical Aristotle actually believed, is pretty similar to Newtonian physics. Instead of "An object in motion stays in motion unless acted on by an ...
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4answers
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What exactly makes a force conservative?

I get that forces can be classified as either conservative or non-conservative, depending on whether the work done in a round trip is zero or non-zero. What property of the force makes it to be, ...
14
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2answers
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Lagrangian and Hamiltonian EOM with dissipative force

I am trying to write the Lagrangian and Hamiltonian for the forced Harmonic oscillator before quantizing it to get to the quantum picture. For EOM $$m\ddot{q}+\beta\dot{q}+kq=f(t),$$ I write the ...
14
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2answers
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Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is a hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic materials, ...
13
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2answers
323 views

Numerical Simulation of Stochastic Master Equation using Stochastic Schrödinger Equation (Wave Function Monte Carlo)

Consider a time independent system coupled to a Markovian bath, the equation of motion for the density matrix of the system has to take the form \begin{equation} \dot{\rho} = - i \left[H,\rho\right] -...
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3answers
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Why can't we make a perpetual motion machine by using a magnet to pull up a piece of metal, then letting it fall back down? [duplicate]

Obviously, a perpetuum mobile isn't possible by any law in physics, because energy can't be "created" or "destroyed", only transformed. This said, I've had an idea for a perpetuum mobile and can't ...
11
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3answers
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What happens to the energy in an ocean wave after it breaks on a reef or the shore?

I understand that the conservation of energy essentially says that "energy can neither be destroyed or created but that it is transferred from one form to another." Given that, on the ocean, wind ...
10
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3answers
820 views

Is a superconductor really a super conductor?

It is known that a superconductor is a material with electrical resistance zero. My question is, it is exactly zero, a theoretical zero, or for practical realistic reasons it is effectively zero?
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A conceptual doubt regarding Forced Oscillations and Resonance

While studying about the Resonance and Forced Oscillations, I came across a graph in my textbook that is given below:- Now, the author writes As the amount of damping increases, the peak shifts ...
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How do you define the resonance frequency of a forced damped oscillator?

Consider a forced, damped harmonic oscillator $$\ddot{\phi} + 2\beta \dot{\phi} + \omega_0^2 \phi = j(t) \, .\tag{1}$$ If I pick a sinusoidal driving force $j(t) = A \cos(\Omega t)$, I find $$\phi(...
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1answer
304 views

A damped harmonic oscillator is NOT a dissipative system?

I know this sounds rather insane, but it says so in my book. The argument is the following: Given a damped harmonic oscilator $$\ddot{q}+\frac{b}{m}\dot{q}+\frac{k}{m}q=0 \tag1 $$ this system can be ...
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How do resistors generate different heat if we make the current fixed and changed the voltage and resistance? Notice the flow of charge is constant

Consider having a circuit which consists of a battery and one resistor. $V = 10$ volts, $R = 5$ ohms, so $I = 2$ Amperes, and $P = 20$ watts. If we double the voltage and resistance, the current ...
9
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2answers
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Can a water vortex (whirlpool) be used to efficiently store energy?

Either a large, constrained cylinder of water or a large volume of open water (perhaps in the ocean) could be persuaded to form a vortex by pumping energy in. The body of water would be acting as a ...
9
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1answer
3k views

How do non-conservative forces affect Lagrange equations?

If we have a system and we know all the degrees of freedom, we can find the Lagrangian of the dynamical system. What happens if we apply some non-conservative forces in the system? I mean how to deal ...
9
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1answer
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Crack pattern of safety glass - what gives rise to spider web-like shape

When (laminated) security or shatter-proof glass fractures, the ensuing crack-pattern is often resembling a spider web, with radial and concentric cracks, see e.g. (Source: http://essentialhommemag....
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1answer
374 views

Caldeira-Leggett Dissipation: frequency shift due to bath coupling

I am trying to understand the Caldeira-Leggett model. It considers the Lagrangian $$L = \frac{1}{2} \left(\dot{Q}^2 - \left(\Omega^2-\Delta \Omega^2\right)Q^2\right) - Q \sum_{i} f_iq_i + \sum_{i}\...
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Would a pendulum swing indefinitely in a frictionless vacuum?

I am attempting to settle a friendly bet. Would a pendulum swing indefinitely in a hypothetical vacuum (i.e. no air resistance) having a hypothetical frictionless bearing (i.e. no energy lost due to ...
8
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4answers
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Can single DC 1.5V battery generate 1500 watts of power?

Suppose there is a DC $1.5\mathrm{V}$ battery connected with $1.5\times10^{-3}\mathrm{\Omega}$ resistor. Then the amount of circuit current is $I=V/R=10^3\mathrm{A}$. (according to Ohm's law) I know ...
8
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2answers
411 views

A false proof of drag force being conservative

Consider a particle moving along some trajectory in the $x$-$y$ plane, in a viscous medium. Then its equation of motion is given by: $$\mathbf{F}_d = - b \mathbf{v} .$$ it's well-known from the ...
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6answers
737 views

Resonance peak broadening due to losses: physical reason

I wonder why when losses are present in a oscillator, the width of the resonance peak is broadened. More precisely: why, when losses are present, can the amplitude reach nearly the maximal one (the ...
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2answers
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How much energy is wasted by a noisy refrigerator?

I recently bought a new refrigerator for my kitchen. The feet are adjustable but I've been lazy. Whenever the motor runs and the feet aren't all touching the floor there is a loud buzzing noise. As ...
7
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2answers
817 views

Damped oscillator: time-reversal, time-translation and dissipation

The equation of motion of a damped oscillator $$\frac{d^2x}{dt^2}+\gamma\frac{dx}{dt}+\omega_0^2x=0$$ which is invariant under time-translation $t\rightarrow t+a$, but not under time reversal $t\...
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3answers
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An example of non-Hamiltonian systems [closed]

I am preparing for the exam. And I need to know the answer to one question which I can't understand. "Give an example of non-Hamiltonian systems: in case of infinite number of particles; for a finite ...
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1answer
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What is the electrical difference between rolled and unrolled extension cables? [closed]

I am talking about the extension cord of length 10 meter or more as follows. The clerk said that it is better to unroll it when using. So what is the difference? I know for alternating current there ...
6
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3answers
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Liouville's theorem and conservation of phase space volume

It can be proved that the size of an initial volume element in phase space remain constant in time even for time-dependent Hamiltonians. So I was wondering whether it is still true even when the ...
6
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2answers
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Why does friction produce heat?

What causes two objects sliding against each other to produce heat? Why don't they generate visible light or something else?
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What are the reasons for leaving the dissipative energy term out of the Hamiltonian when writing the Lyapunov function?

I have a problem with one of my study questions for an oral exam: The Hamiltonian of a nonlinear mechanical system, i.e. the sum of the kinetic and potential energies, is often used as a Lyapunov ...
6
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2answers
118 views

Is there a fundamental reason why “dynamic energy storage” is lossy?

Consider springs and moving masses - both can be used to store energy, the spring via tension $E=\frac{1}{2}kx^2$ and the mass via kinetic energy $E=\frac{1}{2}mv^2$. But day to day experience tells ...
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1answer
104 views

How can dissipative/friction terms be incorporated into a Lagrangian?

I'm trying to find a suitable Lagrangian for a damped harmonic oscillator, a system that satisfies the following equation of motion: $$m \ddot{x} + \gamma \dot{x} + \frac{d\phi}{dx} = 0.$$ What I ...
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1answer
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Why does a rolling sphere stop?

I've just started studying Rotational Mechanics and one thing I'm confused about is that if friction is equal to zero when a body is rolling purely.. then why does a rolling body e.g. sphere.. stop ...
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1answer
185 views

Quantization of dissipative systems?

In undergraduate courses the introduction to Hamiltonian mechanics usually starts from a Newtonian view point. One has equations of motions of the form (not sure if it is ok to use covariant notation ...
5
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2answers
545 views

What physical processes may underly the collisional term in the Boltzmann equation, and how do they increase entropy?

Consider particles interacting only by long-range (inverse square law) forces, either attractive or repulsive. I am comfortable with the idea that their behavior may be described by the collsionless ...
5
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2answers
749 views

What makes quantum decoherence different from dissipation?

From my understanding quantum decoherence and dissipation are completely different ways of modelling information loss to the environment. Dissipation can be modeled using the Caldeira-Leggett model ...
5
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1answer
138 views

Noether's Theorem, Boundary-Bulk, and Open Thermodynamic Systems

Before going any further, I should emphasize that I know we cannot use the action principle for locally dissipative systems or even Noether's theorem for that matter. There are plenty of stackexchange ...
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270 views

Orbit in the vacuum

As the space is a vacuum and there is no friction in space, Can we assume that, if we place an object in gravity in exactly the right distance from a planet with gravity and in the right acceleration, ...
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If string is stretched just by weight, where does the gravitational potential energy goes if only half is converted to elastic potential energy?

If a spring is stretched by a weight of mass m, (so the extension is $\Delta x$) then $ k = \frac W{\Delta x} = \frac {mg}{\Delta x}$. So $ k\Delta x= mg $. When the Spring is stretched by distance $\...
4
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1answer
643 views

Saving energy while charging capacitor

While charging a capacitor by a DC source, half energy is wasted as heat. Can't we save that energy? Here I am talking about $$(1/2)CV^2 $$ which is wasted while supplying $$CV^2$$
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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: ...
4
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1answer
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Why can't friction in an accretion disk radiate away enough of the angular momentum do create inward spiral?

As almost every source that I'd found explains, it was a challenge for scientists to understand the mechanism by which the total angular momentum in the accretion disc was conserved, while taking the ...
4
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1answer
57 views

Examples of non-Hermitian Hamiltonians in open systems?

I have often heard the statement that non-Hermitian Hamiltonians can be used to describe open systems, since the dynamics are non-unitary. However, I have not been able to find any examples of a non-...
4
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3answers
81 views

Is there an intuitive reason the resistance that maximizes power dissipation in this simple circuit has a simple form?

Consider the following circuit: A textbook problem[2] asks to find the resistance $R$ such that the power dissipated in $R$ is maximized (assuming $R_1$ and $R_2$ are fixed). I found that $R$ should ...
4
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1answer
68 views

What is the difference between Non-Conservative and Dissipative?

We often hear these terms. However, they are often confused to be synonyms, but they are not. What are the rigorous definitions of them?
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1answer
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Intuitive explanation for subsonic Fanno flow

In most situations in physics, the effect of kinetic friction is to reduce the macroscopic kinetic energy of a system and convert it into heat, thereby increasing its temperature. but in the case of ...
4
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3answers
101 views

Where does the energy go if the current is induced in a perfect conductor?

Let us rotate a closed circuit made of a copper coil in front of a magnet. This will generate an induced current and all the mechanical energy will be converted into heat through Joule effect. If the ...
4
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0answers
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Are gravitational waves dissipated and what is the mechanism? [duplicate]

I was amazed by the fact that we have been able to detect gravitational waves created thousands of year before they were observed. My surprise is that any wave phenomena I know it is always dissipated,...
4
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1answer
205 views

Is a particle subject to dissipation proportional to its velocity a Hamiltonian system?

Why or why not? I'm pretty sure that this isn't a Hamiltonian system because it involves a dissipation term, but using the Hamiltonian flow it gives me that the system is Hamiltonian.