Questions tagged [dissipation]

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4answers
103 views

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 ...
2
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2answers
107 views

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<<\...
2
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4answers
177 views

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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2answers
321 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
86 views

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
214 views

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 ...
1
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1answer
112 views

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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1answer
137 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 ...
1
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1answer
545 views

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
46 views

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. ...
0
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1answer
30 views

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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2answers
3k views

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
108 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 ...
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3answers
124 views

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
104 views

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 = ...
2
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4answers
118 views

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 ...
0
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1answer
282 views

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 ...
6
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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 ...
2
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0answers
43 views

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 ...
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 ...
0
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2answers
317 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 ...
1
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1answer
60 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 ...
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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0answers
149 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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1answer
47 views

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
34 views

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
376 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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1answer
303 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 ...
0
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2answers
508 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 ...
1
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1answer
53 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 ...
2
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2answers
152 views

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 ...
1
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1answer
41 views

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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2answers
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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0answers
171 views

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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1answer
53 views

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
522 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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0answers
33 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. ...
2
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2answers
108 views

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
79 views

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
65 views

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 ...
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0answers
62 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 ...
2
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2answers
556 views

The Role of Friction in The Lagrangian

I'm pretty new to physics (I am presently taking AP Physics 1 though I am far ahead of that in math) and I was reading this paper that found the equations of motion for Atwood's machine using ...
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3answers
154 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?
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4answers
552 views

Friction during pure rotation

I have already read Role of friction during pure rolling What is the direction of the friction force on a rolling ball? Rolling resistance and static friction and many others But I still have the ...
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2answers
281 views

What is wrong with my perpetual motion machine model? [closed]

I know that perpetual motion machines are not possible and I want to know the reason why will this machine not work. The Car B has a magnetic bulge on top of it and Car B can only move forward. It ...
3
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1answer
70 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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4answers
317 views

Non-conservative forces in nature [duplicate]

We know that gravitational, electrical and magnetic forces are conservative in nature. We also know that friction is fundamentally Electromagnetic in nature. How is it then a non-conservative force?
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1answer
75 views

Potential Energy of Damped Oscillator

In the case of a simple harmonic oscillator we know that the total energy of the system is given as $$E=\frac{1}{2}m\dot{x}^2+\frac{1}{2}kx^2$$ where the potential is $$U=\frac{1}{2}kx^2$$ I read ...
2
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1answer
98 views

Counterexamples to the least action principle

Many of important equations in physics satisfy the least action principle, namely they are Euler-Lagrange equations for some Lagrangian. On the other hand it is known in mathematics that not all ...
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1answer
440 views

Light traveling through different mediums

When light travels from air to another medium, why does the energy of the wave (photon) not change if the new medium is more resistive water, oil etc?