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# Questions tagged [dissipation]

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34 questions with no upvoted or accepted answers
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### 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 ...
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### 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?
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### 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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### 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 ...
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 ...
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### 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 ...
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 ...
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### 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. ...
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 ...
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 ...
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'...
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 ...
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 ...
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 ...
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 ...
29 views

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

What's the "cause" of damping coeff. in springs? Air resistance, friction?
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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### 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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### 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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### 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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### 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 ...
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 ...
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### 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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### 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 ...
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'...
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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### 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 ...
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 ...