Questions tagged [dissipation]

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1answer
47 views

How much energy is lost per bounce with a tennis ball? [closed]

When a tennis ball bounces it loses some energy. How much energy or height is lost per bounce?
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1answer
31 views

Energy dissipation in unitary dynamics

In the context of quantum mechanics it is often (e.g. in several Wikipedia pages, like on Quantum dissipation) stated, that: "If the time evolution of a system is unitary (e.g. always in the ...
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1answer
66 views

Solution of a differential equation in physics

In physics when we solve the differential equation, in some cases we get two part of the solution, one is real and another is imaginary. Some cases we consider that the real part have some physical ...
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1answer
58 views

Is there a relationship between the frequency of a standing wave on an oscillating string and the half-life of its amplitude as it decays?

I'm asking in the context of an experimental exercise where we used a speaker to create a standing wave on a string with constant tension, then turned off the speaker and allowed the amplitudes to ...
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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 ...
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7answers
907 views

Physical Interpretation of an Overdamped Pendulum

Consider a damped pendulum whose equation of motion is given in general by $$m\ddot{x}=-\mu\dot{x}-kx$$ where $\mu,k>0$ Rewrite this equation as $$\ddot{x}+2\gamma\dot{x}+\omega^2x=0,$$ where $...
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0answers
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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 ...
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0answers
57 views

How imaginary part of susceptibility is measure of dissipation?

In linear response theory, we focus only imaginary part of the generalized susceptibility and consider it a measure of dissipation in the system. Can someone throw some light at it that what is meant ...
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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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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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1answer
107 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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2answers
79 views

Can thick fur isolate against heat?

I started writing this question on pet.SE but realised after a while that I think it has more to do with physics than pets but if some admin disagrees, please move it back to pets. I have heard ...
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2answers
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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: ...
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1answer
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Can a Peltier/Seebeck cell transfer energy from a “thermally insulated” system converting (a part of) thermal energy into electrical energy?

Suppose you have a closed system, as per the schema attached below, which walls are thermally insulated. Suppose you want to reduce the temperature of the fluid inside the closed system, without ...
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1answer
49 views

Reduce temperature of fluid inside an isolated system without dissipating heat

Suppose you have a perfectly isolated system filled with a fluid, which cannot transfer heat nor matter to the external environment. Suppose you want to reduce the temperature of the fluid within ...
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0answers
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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3answers
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Work done over a closed loop

Is it true that the work done in the motion of a body over a closed loop is zero for every force in nature?
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2answers
66 views

Thermodynamics: how does the deformation of partially elastic materials produce heat?

When a perfectly elastic material is deformed, the energy associated with the strain remains stored in the body as elastic potential energy, called strain energy. Upon the removal of the deforming ...
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4answers
2k views

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 ...
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1answer
58 views

In Feynman lecture Vol1. chapter12 about friction, $F = μN$ will fail because of the excessive heat generated. Why is that?

$F = μN$ will fail because of the excessive heat generated if the normal force or the speed of motion gets too big. Why is that? "$F = μN$, where μ is called the coefficient of friction (Fig. 12-1)....
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1answer
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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-...
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1answer
46 views

Damped forced Oscillation with variable external frequency

Consider that we have the following forced vibration with an input frequency $ω(t)$ variable in time. $$m\ddot{x}+c\dot{x}+kx = F_0 \sin{(\omega(t) t)}$$ Assuming that the solution must be a ...
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1answer
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Absence of dissipative forces in a reversible process

I can't understand why dissipative forces must be absent during a reversible transformation. Aren't they a way of exchanging heat with ambient? Since the system is allowed to exchange heat with the ...
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0answers
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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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1answer
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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
85 views

Why don't objects bounce infinitely?

I'm computer programmer, and I was making a little test of my “possibilities”, so to speak, so I made a small game with sort of gravity, bouncing ball and walls around. Recently I've noticed that ...
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0answers
41 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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2answers
47 views

Work transfer to the contents of an ideal thermos flask

Assuming the thermos to be ideal and the fluid stored inside it also ideal and non-viscous. For a cold fluid, is it possible to increase the fluid's temperature by shaking the thermos flask? Can the ...
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2answers
604 views

Longest ringing/resonating object [closed]

I am interested in objects which resonate or ring for as long as possible. In particular, I am interested in Crotales (https://en.wikipedia.org/wiki/Crotales), and if it is possible to make a longer ...
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1answer
105 views

Why is it better to accelerate electrons in a linear collider?

An accelerated charge (say an electron for simplicity) emits photons. Changing direction of movement is an acceleration. Electron-positron collisions are preferably done in linear colliders. But why ...
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4answers
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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?
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1answer
53 views

What happens with the energy released after a particles collision?

From the website of CERN: "Collisions in the LHC generate temperatures more than 100,000 times hotter than the centre of the Sun.". My question is, what happens to the energy released after the ...
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0answers
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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 ...
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1answer
56 views

Sign of the work done by dissipation forces

I don't understand this passage from the book I'm reading: Physically, it is clear that a system cannot be conservative if friction or other dissipation forces are present, because $\mathbf{F}\...
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1answer
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Perpetual Motion Machine 1: Magnetic Superconductor Loop Generating Energy with Piezoelectrics [closed]

I know there are a lot of perpetual motion machine designs out there, but I haven't found one that looks like this one. I will use this diagram. Assume the entire ring is made of a superconducting "...
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1answer
76 views

What is complex frequency? [closed]

I am learning EE, and about complex frequencies, but what is its physical meaning? What is it used for? Why is it? And only happen in the laplace transform?
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2answers
142 views

what are the sources of energy loss for a ball rolling down slope?

I am experimenting in lab with an iron sphere rolling down a smooth aluminum ramp. The final velocity is smaller than the one predicted assuming energy conservation (see calculations below), which ...
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1answer
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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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3answers
59 views

Potential, Kinetic, Thermal Energy?

When things move, potential energy turns into Kinetic energy, right? Then how does Kinetic energy convert to thermal energy?
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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 ...
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1answer
52 views

LC-circuit and the current

A capacitor and a coil are charged in the LC circuit. When the circuit switch is closed, the current starts to flow. In theory the oscillations and the current do not deteriorate, but why in reality ...
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1answer
135 views

Why friction causes energy to be lost in terms of heat when it appears to be an energy transfer mechanicsm?

For example, when we move/walk, we apply a force (via friction) on earth, and the earth in turn on us. So essentially I see it as an energy transfer as follows: Suppose I move in same direction as ...
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0answers
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Lagrangian for first order equation of motion? [duplicate]

Let us have the following equation of motion (it might not necessarily correspond to a physical system): $$\dot{x} + a \cdot x + b \cdot x^2 + c=0.$$ I would like to deduce the corresponding ...
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2answers
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Are there any time-periodic solutions to Einstein's equations apart from black holes?

Are there any solutions to Einstein's equations which are periodic in time? A black hole only has mass, charge and angular momentum according to the no-hair theorem. (Although this might just mean in ...
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1answer
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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 ...
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2answers
45 views

Damped drive oscillating systems

I am currently looking at the theory of find the viscosity of and object through damped harmonic motion, and tho it can be done there is obviously a limitation with regrades to the medium. If the ...
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1answer
74 views

Greiner's Green's function for diffusion

I am reading Greiner's "Quantum Electrodynamics". In example 1.5 he derives the Green's function for diffusion. I am stuck on a step in the derivation. He has the defining differential equation as $$ ...
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3answers
135 views

Why do energy transfers always result some heat loss?

explain that energy transfers and transformations in mechanical systems always result in some heat loss to the environment. Like why is it necessary for a heat loss?
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2answers
138 views

How is the simple damper equation derived?

I know the spring is modeled as $F_{\text{elastic}} = k\cdot x$ when the displacements are small since this is empirically based, but what happens with $F_{\text{damping}}=c\cdot\dot{x}$? It is the ...
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2answers
134 views

Harmonic motion with friction [closed]

Consider an undamped mass and spring system with friction. The friction is not proportional to the velocity of the mass. If we solve the corresponding differential equation,the spring will oscillate ...