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Questions tagged [dissipation]

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Energy dissipation for force-free, incompressible Navier-Stokes equation with tangent boundary conditions on bounded domains

I consider the Navier-Stokes equation for uniformly incompressible, force-free, Newtonian fluids with constant viscosity. The equations describing the situation are: $\partial_tv-v\times \text{curl}(...
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1answer
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Conservation of energy in case of a body in motion under non-conservative force [on hold]

A body was initially moving with a constant velocity on a frictionless floor along $+x$ axis. Then a constant force is applied by me along $-x$ axis .The applied force does negative work on the body ...
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Exponentially decaying force ODE [closed]

This question is proving to be really tricky. Would solving this equation be any different to solving an analogous one involving a periodic external force? $$m\frac{d^2x}{dt^2}=-kx-\Gamma \frac{dx}{...
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1answer
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Is the violation of time-reversal always associated with the violation of time-translation and vice-versa?

Is the violation of time-reversal symmetry always associated with the violation of time-translation symmetry? What about the converse? Is it possible for one to be violated while the other remaining ...
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Significance of the complex component in the underdamped harmonic motion equation [on hold]

The following differential equation represents the motion of a body of mass $m$ and displacement $x$ from the mean position, that is attached to a spring of force constant $a$ and viscous damping ...
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1answer
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Why do we need to have a low voltage drop over long distances in transmission of electricity? [closed]

It is said that AC is preferred over DC because of the negligible voltage drop over long distances. How does that work?
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2answers
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Why does height affect bounce efficiency?

I recently conducted an experiment, where I dropped tennis balls from various heights and recorded their rebound heights. The higher the drop, the higher the rebound height, obviously. However, the ...
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Motor/energy considerations

A motor is a device into which energy is transferred by electrical transmission while energy is transferred out by work. we know that the power delivered by an emf source is P=I^2*R. now coming to ...
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4answers
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How do charges lose electrical potential energy when going through a resistor?

I can understand that the charges need to do work against the resistance - which transfers energy to forms such as light, heat, etcetera - using the electrostatic force provided by the battery ...
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2answers
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Exact equation of exponential curves of underdamped harmonic motion

I was studying the underdamped harmonic motion and got curious about the fact that the decreasing exponentials $\pm Ae^{-\gamma t}$ are good approximations only for light damping $(\gamma<<\...
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4answers
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Why do we use the RMS but not the fourth root mean quad?

Why do we use the power of $2$? What is the relation between this and having the same heat energy in both AC and DC?
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Would it be appropriate to say that in presence of Non-Conservative Forces, the Entropy of System Always Increases?

Would it be appropriate to say that in Presence of Non Conservative Forces the Entropy of a system would always increase? Can we relate Non-Conservative Forces and Entropy in some way? I intuitively ...
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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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Do power supplies have to heat up?

Is there a fundamental reason why a power supply, say, from 120v AC to 12v DC, has to lose some power to heat dissipation? I am not asking why current engineering solutions do; I'm aware that ...
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1answer
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Maxwell's wheel and friction

We experimented with the Maxwell's wheel today and at the end we were asked about why does this apparatus stop since there is conservation of energy. I did some research and apparently there is a type ...
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1answer
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PT-symmetric hamiltonians: Transition from non-dissipative to dissipative system

It is known that Spectrum of a non-hermitian hamiltonian is complex ($E_n-i\gamma_n$) and they represent the dissipative system. eg, Damped harmonic oscillator(DHO), where $E_n$ are the energies of ...
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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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1answer
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How is the rate of decay of a Newton's Cradle affected by the number of spheres in the system?

How does the number of spheres in a Newton's Cradle affect its rate of decay? (assuming only 1 sphere is released initially) From experiment, I observed that the rate of decay of a 5 sphere Newton's ...
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2answers
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Force, work and the apparent disappearance of Mechanical Energy [duplicate]

A man exerts force on a wall of bricks. The man must have consumed the energy he possessed (mechanical energy?) to exert the force. The man sweats and tires himself out but the wall does not move. ...
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1answer
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Large Damped Harmonic Oscillator misunderstanding

So I'm confused, here with what is highlighted. When the book says of "order $1/y_-$" you will reduce the displacement by a factor of $1/e$. Does of order mean when the time is equal to $1/y_-$, if ...
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Principle of least action for dissipative systems [duplicate]

I am trying to solve a problem with involves friction, and am having trouble solving it with $F=ma$. I am considering to use Lagrangian mechanics, but I am puzzled. There doesn't seem to be a ...
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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 ...
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2answers
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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 ...
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3answers
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What happens to the heat generated in an irreversible process?

I know that a reversible process does more work than an irreversible process and that extra work is turned into heat. But what does that heat do? Does it increase the temperature?
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3answers
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Kinetic Energy with constant velocity

I am sorry for the question, but I am a noob in Physics. I don't understand why in the kinetic energy's formula the distance is out of the equation. Kinetic Energy formula: $$K = \frac{1}{2}m v^2 = ...
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4answers
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In a simple battery + resistor circuit, what form of energy is lost from the electrons upon exiting the resistor?

I will give this question a little context. Firstly, as I understand it, as soon as I "close the switch" on a circuit, electric current pretty quickly establishes a steady state where, at any given ...
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1answer
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Magnetic Turning Wheel [duplicate]

So a few years ago I came up with the idea of a magneticly powered wheel that could be attached to a generator and power it, it would not be infinite as over time magnets lose their power yet I think ...
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1answer
2k views

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 ...
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0answers
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Potential gravitational energy versus potential spring energy [duplicate]

My textbook points out the following predicament, and I do not know the answer, despite a lot of thinking: A spring is hanging of a ceiling and a mass is attached. As a result the spring descends to ...
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3answers
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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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2answers
107 views

Why is sound produced when we hit a metal? [duplicate]

We all know that metal are sonorous and produce sound on hitting but why is sound produced I thought that it might be a way of energy released on inelastic collision but then why not heat as heat is ...
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1answer
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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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2answers
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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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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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1answer
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Phase shift of damped mass on spring with moving source [closed]

I have a setup with a moving (upwards, downwards) board on which there is a spring mounted on the edge. The spring has a mass $m$ on its end and is damped in some sort of liquid. What methods could I ...
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1answer
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Is there a temperature limit for the magneto caloric effect?

Suppose a thermally insulated box which has to keep its inner temperature below a certain limit, and suppose a high temperature outside of the box, such as a fire at 1000C. Would it be possible to ...
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1answer
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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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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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2answers
186 views

Why does a ball rolling without slipping stop due to friction? [duplicate]

I'm confused on a scenario. If we roll a ball on a horizontal surface and it rolls without slipping it should eventually stop due to friction. However rolling without slipping means the velocity at ...
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1answer
51 views

What is the energy dissipation of an ideal launch loop?

Dynamical structures for space access use a stream of electromagnetically accelerated and levitated pellets that moves faster than escape velocity to maintain megascale structures and transmit force ...
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2answers
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Does current in a superconducting circuit ever decay?

Once a current has been started in a superconducting loop, say by induction, will it truly stay on forever or is it intrinsically doomed to decay, albeit slowly? For example, can radiative losses ...
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1answer
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Approximating mechanical systems with high friction

I remember to have read (a long time ago) that if I have a mechanical system $\ddot x=\frac1mF(x)$ with a high friction, then I can instead study the other system $$\dot x\sim F(x)$$ to get an ...
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How to debunk this perpetual motion machine? [duplicate]

I know it's impossible. I normally find the flaw behind the principle, but this one is hard to crack. The two wheels are geared together, so that no magnet on one wheel "backlashes" the wheel in a way ...
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Can you give an example of a “non-conservative field force”? [duplicate]

I need an example of a non conservative field force,if there exists any. If in the case of conservative field force work done is stored as potential energy then what can we say in the case of non-...
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1answer
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Resistor as an ideal machine

Isn't a resistor an ideal machine? It can convert electrical energy into thermal with an (or almost?) 100% efficiency.
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1answer
229 views

Energy dissipated by friction vs Work done by friction

Is energy dissipated by friction the same as work done by friction where the equation is W(friction) = Ff * d cos theta . However, since work is the transfer of energy and not energy itself then is ...
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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. ...
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2answers
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Why is a bath necessary for nonconservative forces in quantum mechanics

In classical mechanics, it's straightforward to include nonconservative forces. For a particle in 1D, Liouville's equation becomes, $$\partial_t \rho + \dot{q}\partial_q \rho + \dot{p}\partial_p \rho ...
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1answer
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Why is there no friction energy?

Can anyone briefly explain to me why is there no term for frictional energy when they often referred to work done by friction instead? Thank you
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1answer
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Is motion a form of energy?

I think I am running into a semantics difficulty. Loosely speaking when energy is converted from potential to kinetic is the motion a form of energy? Let us use an example: A ball drops to ...