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Questions tagged [dissipation]

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34 questions with no upvoted or accepted answers
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4
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3answers
102 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 ...
3
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3answers
183 views

How does an electric dipole lose its energy while aligning with a uniform electric field?

How does an electric dipole lose its energy while aligning with a uniform electric field--through heat or light?
3
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1answer
75 views

Landauers Principle Derivation

I read about Landauer's principle and was wondering about the implications from it's original derivation. Landauer derived his principle straight foward from the second law, but I see people favoring ...
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0answers
62 views

Physical origin of gradient-like system with nonautonomous damping term

I am in mathematics major, and I am considering the equation $$\ddot u(t) + \gamma(t) \dot u(t) + \nabla \phi (u(t)) = g(t), $$ where $\phi: \mathbb{R}^n \to \mathbb{R}$ is of class $C^1$, convex and ...
3
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3answers
699 views

Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
2
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0answers
45 views

How does friction cause a spinning top to fall?

I am wondering how friction can create a torque to change the angular momentum and cause a spinning top to tilt, like in the diagram of a close up of the rounded tip of a top while the angular ...
2
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0answers
133 views

Does the Lindblad equation satisfy a fluctuation dissipation relation?

The fluctuation dissipation relation is usually stated in terms of an identity that relates the retarded, advanced and either the Keldysh or time-ordered correlators. This is easily enforced in ...
2
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0answers
289 views

Liouville's theorem for systems with dissipation described by a single hamiltonian

Following this link, one can treat dissipation in the lagrangian by using a factor $e^{\frac{t \beta}{ m}}$ in addition to the Lagrangian $L_0$ of a system without disspation: $ L_0[q, \dot{q}] = \...
1
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2answers
129 views

When you have engine at idle and turn your car, where does the kinetic energy go?

When you turn the front wheels to the right for example, your car will tend to continue in its original forward direction. However, there is friction between the wheel and the ground that prevents it ...
1
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1answer
65 views

Guitar string - feedback from the body

This is a question about the frequencies that remain on the string during the decay of vibrations. As I understand it decay occurs because of the: a- Internal damping of the string. This is due to ...
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0answers
176 views

Definition of Ohmic bath and damping force

I have read the Wikipedia article on quantum dissipation where it is talking about the bath spectral function. The bath spectral function provides a constraint in the choice of the coefficients $...
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0answers
35 views

Is it possible to find an operator on wavefunctions that results in nonconservative forces?

The Schrodinger equation for a particle in a potential is, $$i\hbar \partial_t \varphi = \left( \frac{p^2}{2m} + V(x) \right) \varphi$$ where p is the momentum operator and $V$ is the potential. ...
1
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1answer
235 views

Determination of spring constant $k$ for an elastomer

Primary Question: How can you determine the spring constant $k$ of an elastic material? I was recently tasked with finding the spring constant for a series of elastomeric materials, the first of ...
1
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1answer
340 views

Why does a longer string vibrate longer before the damping brings it to rest?

While performing string vibration experiments under the boundary condition that both ends are fixed, I observed that the damping of the wave is much larger when the size of the string is smaller and ...
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0answers
99 views

How to physically interprut coupling to a heat bath?

In studying quantum optics I commonly see and use a model environment represented as a sum of harmonic modes. I am familiar with the idea of quantizing Maxwell's wave description of light so it doesn'...
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0answers
567 views

Friction in Lagrangian formulation

We know the Lagrange equations are: $$\frac{\partial \mathcal{L}}{\partial q_i}-\frac{d}{dt}\left(\frac{\partial \mathcal{L}}{\partial \dot{q_i}}\right)=0.$$ Then, when we add friction in there, we ...
1
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1answer
246 views

String vibration and damping

In case of a home experiment about string vibration under the boundary condition $$y(l,t)=y(0,t)=0$$ Where $y=$ the displacement of the string at spatial co-ordinate $x$ and at time $t$, I observed ...
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2answers
41 views

Electrical generators: power balance

Usually power generating synchronous generators are rated at around 85-90% efficiency. Curiosity struck me as of how a generator with field coils can ever go to such an high efficiency. My thought ...
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0answers
45 views

Experimental lower bound on the lifetime of a supercurrent?

Nothing is perfect, everything has friction---except in quantum physics, where macroscopic superconductors allow for dissipationless currents. It's an astounding theoretical prediction, and so it is ...
0
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1answer
29 views

What's the “cause” of damping coeff. in springs?

What's the "cause" of damping coeff. in springs? Air resistance, friction?
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0answers
41 views

Calculate viscous damping coefficient given force

With a force metre I recorded the force vs time of a spring with a disk on the end in water, experiencing viscous damping, during damped oscillatory motion. I pulled the disk to the bottom of the ...
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24 views

Solutions to Non-Ideal Gyroscopic Equations

In my work with gyroscopes, I have correctly derived the Lagrangian of a 3d top or gyroscope as $L=\frac{1}{2}I_{xy}(\dot{\phi}sin^2(\theta)+\dot{\theta}^2) + \frac{1}{2}I_{zz}(\dot{\phi}cos^2(\theta)...
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41 views

Klein-Gordon/Maxwell Equation: dissipative or dispersive?

In Aspects of Symmetry, Coleman says (p. 185) ''Most of the simple field theories with which we are familiar have the property that all of their non-singular solutions of finite total energy are ...
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42 views

Is there a formula showing the relationship between the number of iron cores and the output voltage of a transformer?

I know the relationship between number of turns, current and voltage of a transformer, but is there a formula showing the relationship between the number of iron cores and the output voltage of a ...
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0answers
54 views

Where exactly does the drag force come from when using eddy currents?

I read the Wikipedia page on eddy currents and the explanation for braking confused me At the leading edge of the magnet (left side) by the right hand rule the counterclockwise current creates a ...
0
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1answer
118 views

Airflow velocity and volume loss due to friction

I have a vacuum that the manufacturer claims capable of moving 20,000 cfm of air. In my application we often connect 150 feet of 6 inch diameter, smooth bore, flexible tubing to the vacuum. I know ...
0
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1answer
422 views

How does temperature affect sound wave dissipation in air?

Sound waves dissipate in any material such as air, but if temperature decreases or increases; how would the increase or decrease in temperature affect the dissipation?
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63 views

Can torsional force be used to harvest gravity?

I am curious if an idea I have will work or if it is the result of a lack of understanding of the physics involved. I am expecting to be disproved. Please excuse any lack of understanding on my part ...
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0answers
106 views

Deterministic non-harmonic motion of a single spring

Is there anything describing a spring's motion when e.g pulled and released, or pushed and released, with no mass-body attached to the spring. I.e not your usual "mass motion on a spring"-equation. I'...
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1answer
477 views

Energy dissipation in current flow

In section 4.8, Energy dissipation in current flow, of Purcell and Morin's Electricity in Magnetism, the expression for the power expended by a resistor is derived. The sections includes the following ...
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3answers
1k views

When is mechanical energy ever conserved for inelastic collisions?

So as I was taking a test today I encountered an intriguing question, the question came in two parts. The first parts, which I answered quite easily, was about whether or not mechanical energy is ...
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1answer
53 views

Change of energy into friction?

If I am pushing a car and it does not move, I am doing no mechanical work. However, I am changing the energy that was stored in my cells into heat energy (maybe sound energy if my hand slips off the ...
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1answer
112 views

Hamilton's equation of motion with other momentum

I wrote here a problem couple days ago. I figured out what was the problem there, but now it made another problem. Sorry for similiar question. I'm trying to draw phase portrait for my ODE and for my ...
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1answer
38 views

Dissipation of energy in inductors

Please explain the dissipation of energy in a circuit containing a resistance and inductor after the switched in the circuit is opened.I mean how do you explain that the energy that is across inductor ...