Questions tagged [dissipation]

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141 views

Elastic or inelastic collision?

When two billiard balls collide in normal situation (on earth) we hear the sound due to their impact. This is a sufficient proof that the collision is inelastic in nature due to loss of energy in the ...
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1answer
442 views

Why the name “relaxation time”?

Trying to explain to myself the Stokes number, I was linked by Wikipedia to this article: http://en.wikipedia.org/wiki/Relaxation_(physics) In that article, if $\tau$ is the relaxation time, then ...
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2answers
4k views

Why do power lines use high voltage?

I have just read that using high voltage results in low current, which limits the energy losses caused by the resistance of the wires. What I don't understand is why it works this way. Does it have ...
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3answers
299 views

RMS Values in AC Circuits

When do you use RMS values when calculating power? My physics textbook provides several equations for determining the power dissipated in AC circuits. For example, there are power equations using ...
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2answers
771 views

What is the difference between damping and elasticity forces?

From DYNAMICS OF STRUCTURES, Third edition, by Ray W. Clough and Joseph Penzien Damping has much less importance in controlling the maximum response of a structure to impulsive loads than for ...
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1answer
385 views

Lagrangian for an oscillator with position-dependent damping

I wonder if the equation of motion of an oscillator with (position-dependent) damping \begin{equation*} \ddot{x}+\gamma(x)\dot{x}+\omega_{0}^{2}x=0 \end{equation*} can be derived directly from ...
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114 views

Superconductor surface resistance

If the superconductive state is due to a phase transition from ohmic to a state a zero-resistivity, why the superconductive materials are usually identified by their surface resistance, or by their ...
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2answers
673 views

If I charge 3 capacitors in series, then connect themin parallel, where does the remaining energy go? [duplicate]

I'll get into the math straight away $C_1, C_2, C_3$ each are charged to $q$. The energy is $$\frac{q^2}{2\left(\frac{1}{\frac{1}{C_1}\frac{1}{C_2}\frac{1}{C_3}}\right)}$$ $$\frac{1}{2}\left(\frac{q^2}...
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1answer
200 views

Why does the photon travel differently in Earth's Atmosphere?

Take a box T.V. and place it out side and notice the farther away you walk from it the red color fades only leaving the blue color. Why is that? Deep sea plants are commonly found to be red in color ...
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1answer
438 views

Meaning of Non-dissipative Dynamical System

What does it mean to say that a dynamical system is non-dissipative? I am particularly interested in an answer in the context of field theory or particle dynamics. Also, how does this imply that we ...
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1answer
3k views

Why does a rolling sphere stop?

I've just started studying Rotational Mechanics and one thing I'm confused about is that if friction is equal to zero when a body is rolling purely.. then why does a rolling body e.g. sphere.. stop ...
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2answers
688 views

Why isn't the resonance frequency of a vibration the damped frequency? [duplicate]

I had studied the damped forced vibration and had come to know that the angular speed of force which creates resonance is Which is counter-intuitive to me that the angular frequency should match ...
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0answers
131 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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2answers
73 views

Is it true that an object, in course of its motion, always seeks the position of minimum potential energy?

I have heard the statement, in a Classical mechanics course, that the motion of an object is always toward the position of minimum potential energy. I don't think that this statement correct because I ...
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3answers
198 views

Energy doesn't get lost? Basic understanding, please [duplicate]

If its true that energy isn't lost, its just transferred, where did the energy go from a falling object that hits the floor and stays there? It started with the most gravitational potential energy, a ...
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1answer
469 views

Why power dissipated over a resistor relies upon intensity not upon voltage

For computing the power dissipated over a resistor the correct formula is $P = R \times I^2$. Why, in other purposes equivalent, $P = \frac{V^2}{R}$ is not good? I can imagine that the actual current ...
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2answers
2k views

Frequency of Damped Vibrations [duplicate]

In the chapter sound, my book states that the Frequency of damped vibrations is less than the natural frequency but I could not understand this because in damped vibrations the amplitude decreases and ...
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1answer
164 views

Relation between Diffusion in Momentum and Decoherence

I have noticed in several sources (for example, eq. (3.151) of Decoherence and the Appearance of a Classical World in Quantum Theory and eq. (5.40) of Decoherence, einselection, and the quantum ...
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1answer
3k views

How do non-conservative forces affect Lagrange equations?

If we have a system and we know all the degrees of freedom, we can find the Lagrangian of the dynamical system. What happens if we apply some non-conservative forces in the system? I mean how to deal ...
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2answers
228 views

Which period should be used to determine average speed of a damped oscillator? [closed]

For a damped, driven oscillator, show that the average kinetic energy is the same at a frequency of a given number of octaves* above the kinetic energy resonance as at a frequency of the same number ...
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3answers
441 views

RLC circuit - calculating resonant frequency

If I take a series RLC circuit connected to a battery, the impedance is minimized when $\omega = \frac{1}{\sqrt{LC}}$. I also know that the series RLC circuit is analogous to a damped driven harmonic ...
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3answers
2k views

If string is stretched just by weight, where does the gravitational potential energy goes if only half is converted to elastic potential energy?

If a spring is stretched by a weight of mass m, (so the extension is $\Delta x$) then $ k = \frac W{\Delta x} = \frac {mg}{\Delta x}$. So $ k\Delta x= mg $. When the Spring is stretched by distance $\...
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1answer
5k views

Does fluid speed affect liquid cooling?

If you have a liquid-based cooling system, like the loop in the picture below, does the fluid speed actually matter? I can see how cycling the liquid too slowly would be bad, since the fluid would be ...
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2answers
2k views

How does viscosity cause dissipation? [closed]

I am not a physicist so bear with me. I'm trying to understand the mechanism through which energy is dissipated in a fluid or solid. Often the explanation is that it happens due to viscosity or ...
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1answer
439 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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1answer
53 views

DPD weight function

I was wondering about the connection between the weight function of the random force and the conservative force between DPD particles in a standard DPD simulation. Both usually have the form [Groot ...
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3answers
2k views

Work done in thermodynamics [duplicate]

The work done in thermodynamic process is given by the integral of Pdv and also we can write so assuming a quasi static process between two points. But this work is then non dissipative work or work ...
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1answer
2k views

Crack pattern of safety glass - what gives rise to spider web-like shape

When (laminated) security or shatter-proof glass fractures, the ensuing crack-pattern is often resembling a spider web, with radial and concentric cracks, see e.g. (Source: http://essentialhommemag....
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2answers
862 views

How to calculate energy loss in a rotating shaft?

Please help me with proper formula for below example. Imagine a rotating shaft 'X' with 2 gear wheels 'a' and 'b' of same dimensions. If energy applied to gear 'a' on the shaft through source A ...
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2answers
827 views

Damped oscillator: time-reversal, time-translation and dissipation

The equation of motion of a damped oscillator $$\frac{d^2x}{dt^2}+\gamma\frac{dx}{dt}+\omega_0^2x=0$$ which is invariant under time-translation $t\rightarrow t+a$, but not under time reversal $t\...
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1answer
63 views

What kind of damping is this $F = -ax|x'|$?

From Applied Mathematics by Logan: A mass hanging on a spring is <...> governed by $$mx'' = -ax|x'| - kx$$ where $-ax|x'|$ is a nonlinear damping force. I looked up "nonlinear damping" and ...
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6answers
8k views

Why does a system try to minimize its total energy?

Why does a system like to minimize its total energy? For example, the total energy of a $H_2$ molecule is smaller than the that of two two isolated hydrogen atoms and that is why two $H$ atoms try to ...
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1answer
207 views

Are all forces given by a field conservative forces?

When teaching us electromagnetism, our professor first introduced us to the concept of "field". Several lessons later, he proved that electric field force is a conservative force. But I think the ...
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2answers
3k views

Why does a ball eventually stop?

I was wondering, if the force of friction with the ground does not make any work on the ball and just give it the necessary torque to rotate (hence the consideration of static friction coefficient in ...
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2answers
6k views

Difference between stiffness and damping?

I understand stiffness as the extent to which an object (e.g. a mass spring) resists deformation from an applied force, or the rigidity of an object. And I understand damping as the energy ...
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2answers
583 views

If I spinned a fan in a vacuum it will keep spinning forever. Why can we not make energy out of it? [duplicate]

Suppose we created a vacuum and spinned a turbine inside it with some amount of force. According to newton's second law it will keep spinning as there is no air resistance, so why can we not make ...
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1answer
187 views

Quantization of dissipative systems?

In undergraduate courses the introduction to Hamiltonian mechanics usually starts from a Newtonian view point. One has equations of motions of the form (not sure if it is ok to use covariant notation ...
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3answers
670 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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4answers
820 views

Why does work done ultimately culminate as wasted heat?

Come to think of it, the work done on a body is converted into some form of energy.But why is it that it ultimately tends to produce heat? In physics we all talk about energy dissipation in the form ...
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4answers
768 views

Where does the energy go when engine braking?

If you're in gear in a car and not accelerating, the car slows down faster than it would from just air resistance and tire deformation. In normal braking, the energy is turned into heat from the brake ...
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1answer
4k views

Perpetual motion machine with magnets [duplicate]

I have been recently made aware of the following motor, which uses two magnets and a wheel to generate motion, and the creator of this machine claims that this motion is perpetual. Here is a YouTube ...
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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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0answers
84 views

Friction in Lagrangian Method [duplicate]

A uniform, flexible chain of length $l$, mass $m$, hangs off a frictionless table-top of height greater than $l$. The length of the part of rope hanging off is $x$. Gravity accelerates the part of the ...
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0answers
136 views

Are gravitational waves dissipated and what is the mechanism? [duplicate]

I was amazed by the fact that we have been able to detect gravitational waves created thousands of year before they were observed. My surprise is that any wave phenomena I know it is always dissipated,...
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1answer
675 views

Saving energy while charging capacitor

While charging a capacitor by a DC source, half energy is wasted as heat. Can't we save that energy? Here I am talking about $$(1/2)CV^2 $$ which is wasted while supplying $$CV^2$$
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0answers
136 views

Wronskian of complex second order linear differential equation [closed]

While studying certain analogue gravity models I came across a differential equation of the form: \begin{align} \frac{d^2y}{dz^2} + \omega^2 (z)~ y(z) = 0 \end{align} where $z$ is a complex variable ...
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5answers
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A conceptual doubt regarding Forced Oscillations and Resonance

While studying about the Resonance and Forced Oscillations, I came across a graph in my textbook that is given below:- Now, the author writes As the amount of damping increases, the peak shifts ...
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1answer
82 views

Help with my bouncy ball lab (I know the factors just not how to approach them) [closed]

In my physics lab we need to determine the factors that account for the energy "loss" during a high bounce ball bounce. I know that energy is "lost" (not really) to heat, air resistance, and sound. ...
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8answers
495 views

Why not use our own light production to produce new energy instead of wasting it?

Why don't we use our own light production at night (I mean home, buildings, streets,..., lighting) to charge photovoltaic panels instead of wasting it?
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2answers
593 views

Dissipative forces and reversible processes

A book that I have contains the following lines: For a process to be reversible, the dissipative forces such as viscosity and friction should be absent. My question is why?