Questions tagged [dissipation]

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68 views

Do resistors heat up with left-over amps?

Apologies in advance if I misunderstand and for my bad explanation. I have heard that resistors heat up when there are left over amps that are not being used. If this is the case, why do most home ...
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3answers
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How is energy really dissipated in an electric circuit?

I've heard that in a circuit, energy is provided to separate components (lamps, motors, etc.) because of the flow of electrons. How is this possible? Since energy cannot be created, where is this ...
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Where does energy go in joining capacitors of different capacitance charged by different potential, hypothetically assuming no resistance in circuits?

I don't understand why there is any change in initial and final energy since we have already assumed a perfectly conductive circuit. I mean, theoretically at least, there should be no change in energy....
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2answers
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Energy lost in a do-nothing machine

I recently came across this large (and very cool) do-nothing machine: do-nothing machine (video) Commentators on the internet have mentioned that the machine wastes energy, and therefore doesn't "...
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0answers
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Reversibility of equation $F=mv$ [duplicate]

Please read the following text. This text is part of Leonardo Sauskind's book. It says that the relation F = m v is reversible. Why?
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1answer
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Reversibility of the rules of classical mechanics [closed]

In the book of classical mechanics, Leonard Susskind says that Aristotle's equation of motion (F = mv) is reversible. But in the second lecture Theoretical Minimum 'videos say that F = mv is not ...
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1answer
39 views

In a simple circuit with only cell and wire, where is the electrical energy lost (what causes potential difference)?

Imagine a simple cell circuit with a nine volts cell. Because of the cell, there is a potential difference of 9V between 2 points on the circuit. Because $$Energy at a point = charge * electric ...
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1answer
41 views

Confusion about energy changes

A bicyclist first goes up and then down a hill with constant speed. He ends up at the same height as at the start? I dont understand why to explain the law of conservation of energy my book has stated ...
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2answers
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Why does the free vibration of the spring-mass system not work in actual experiment?

Why do we not get free vibration of the spring mass system forever in reality?
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1answer
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Why does the angular frequency ω changes during the damping oscillations?

I can understand why $ω$ in the damped system is smaller than the intrinsic $ω_0$, but why does he say 'angular frequency $ω$ changes during the damping oscillations'? The equation between $ω$ and $...
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1answer
34 views

What are the factors that affect the dampening of spring-mass system? [closed]

I'm trying to investigate how different values of spring constant affect the changes in amplitude and period of oscillations while the spring-mass system undergoes dampening. However, I have to make ...
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2answers
58 views

Why do waves disappear after some time?

When a stone is thrown in water then transverse waves are formed. But they get slow and disappear after sometime. Why? Similarly it happens in longitudinal waves. When we speak, after sometime our ...
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0answers
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Statistical definitions of heat and work

My understanding of heat and work from a statistical mechanics perspective (mainly extracted from Schrödinger's Statistical Thermodynamics) is as follows. We have some system, let us say a box of gas....
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2answers
154 views

A proof that air resistance isn't conservative

I want to show that a force depending on the velocity $\dot{\underline{r}}$, where $\underline{r}$ is the position vector of a particle, cannot be conservative since there is energy dissipation. Here, ...
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3answers
113 views

Why does the reversible adiabatic expansion do more work on the surroundings compared to the irreversible adiabatic expansion?

I am wondering why a reversible adiabatic expansion results in a higher work output on the surroundings though the irreversible adiabatic expansion has to overcome the frictional force and therefore, ...
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3answers
832 views

How do we dampen a spring-mass system with respect to time?

Here https://en.wikipedia.org/wiki/Harmonic_oscillator we have an equation for displacement of a mass on a string as a function of time. ${\displaystyle x(t)=A\cos \left({\sqrt {\frac {k}{m}}}t\right)...
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4answers
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Does friction do work or dissipate heat?

I know there are a bunch of similar questions but I read through them all and they don't answer my question. Let's say I give a box on a floor an initial "kick" of force such that it has kinetic ...
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1answer
25 views

Cound someone help to check if this paper is talking about sound absorption coefficient of the air?

I am trying to compute the distance I stand away from a sound source and still can detect the sound although I cannot hear clearly what the speaker is saying. Given the threshold of human hearing and ...
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4answers
173 views

How do I include friction due to normal force in Lagrange Equations?

I am going through the Goldstein book on classical mechanics and the after he derived the Lagrange equations he used Rayleigh dissipation function to include friction as a generalized force. In school ...
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1answer
41 views

Quantising a Damped Mass on a Spring

Background: this question discusses Lagrangian/Hamiltonian formulation of a dissipative problem. However, I'm not clear if this can be made quantum and would like a more explicit roadmap if possible. ...
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1answer
51 views

How do electrical motors obey the conservation of energy?

Feynman introduces the concept of an electromagnetic motor with this diagram. I believe I understand why the wire turns when there is current through it, because $F = q(\mathbf{E} + \mathbf{v} \times ...
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2answers
484 views

Calculating the total time elapsed until two pendulums “stop colliding” gives a divergent result [closed]

Setup Consider the following situation: Two (small) balls hang by two identical ideal threads, such that in their initial states the threads are perfectly vertical. The two balls are moved by small, ...
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2answers
99 views

Why must all natural processes be irreversible?

My thermodynamics lecturer was talking about reversibility and the idea of spontaneous change and he mentioned that all natural processes are irreversible. Can someone offer some sort of proof or ...
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1answer
26 views

How the total energy of a LC oscillator remains unchanged while placing a coil near the inductor of the LC oscillator?

If the capacitor is initially charged with Q charge and then conected to a inuctor then discharging takes place and the energy stored in electric field gets converted into the energy stored in ...
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0answers
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Where are the hysteresis losses?

I have some troubles to understand what are the hysteresis losses on a magnetic hysteresis loop of a ferromagnetic material. First question, is there a law which say that the product of the magnetic ...
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3answers
76 views

Conservation of energy in collision if A hits B but fails to move B

If body A hits body B but fails to move B what happens to its kinetic energy? There is no increase in potential energy. So what is accounting for this loss?
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1answer
59 views

Doing work against the friction force, temperature, and heat

In Feynman's his introduction to the second law of thermodynamics, he said, We know that if we do work against friction, say, the work lost to us is equal to the heat produced. If we do work in ...
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2answers
67 views

How can the energy be conserved, as negative work done on a moving body also wastes energy stored in my muscle? [closed]

Suppose a particle like object is moving on a frictionless surface. If I push it back to reduce its kinetic energy, it also wastes energy stored in my body. Is energy really conserved here? Again, ...
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6answers
100 views

Can we keep a photon bouncing of mirrors for a long time (eg days)? [duplicate]

If a photon is sent into a box with perfect mirrors aligned in a way that it won’t ever be reflected out, is it possible to hold the photon for extended lengths of time with its quantum properties ...
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6answers
165 views

How the moon takes energy from Earth (if at all)?

At least twice (on the comments of this answer, and mentioned in passing on this book), I have read that the moon takes energy from Earth due to tidal drag. The notion seems that: a) energy must ...
2
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1answer
41 views

How does the tuned mass damper on Taipei 101 work?

I'm interested in how the tuned mass damper on the top floors of Taipei 101 works, particularly how do engineers ensure that it dampens oscillation rather than making it worse. The damper can be ...
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1answer
54 views

Problem with understanding non-conservative systems

I'm trying to understand non-conservative systems. I'm struggling with lagrangian/hamiltonian mechanics and I read that classic lagrangian/hamiltonian mechanics can't be used for non-conservative ...
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2answers
95 views

Why is the power unchanged by a transformer?

If we have a step up transformer then the voltage at the secondary side will be more than the voltage at the primary side. Since we all know that POWER = VOLTAGE * CURRENT and because voltage at the ...
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1answer
36 views

Sound energy transformation

What does sound energy transforms into? Energy can neither be created nor be destroyed. So what does sound energy change into?
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1answer
38 views

Does every form of energy tends to get converted into heat?

I am not sure that each and every form of energy gets converted into heat but I observed that in most of the cases it happens.For example:- we feel hot when our body is exposed to light, our room ...
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1answer
46 views

On a dam spillway, where does the potential energy of the water go?

Dams are used to generate electric power by running the water through turbines. This uses the potential energy of the water, first converting it to kinetic energy of linear water movement, then ...
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0answers
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Symmetrical design of a tuning fork [duplicate]

I was reading Ch. 10 of Kleppner and Kolenkow and I came across an explanation which said "The energy loss in a tuning fork is primarily due to heating of the metal. Air friction and energy loss to ...
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1answer
34 views

$Q$-factor of oscillator [duplicate]

Given the equation for a damped oscillator is $$\ddot{x}+\gamma\dot{x}+\omega_0^2x=0$$ Is the $Q$ factor of the system given by $\omega_0/\gamma$ or $\omega_0/2\gamma$? I have seen both forms come ...
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0answers
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Perpetual Motion Explanation [duplicate]

Hello could someone explain the reason why this machine does not work. There is an explanation in the text but I cannot seem to follow it. Here is the link - it's the buoyant spheres perpetual motion ...
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1answer
21 views

Energy dissipation and work of adherence force

Assume you are pushing a heavy item. But it's not moving. So there is no work, and there should also be no dissipation of energy $P=F v=0$, since the forces don't work. But we see that it does demand ...
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0answers
47 views

I want to know more about this specific perpetuum mobile [duplicate]

Sorry for beeing another noob asking stupid questions, but I just wanna know more about this specific perpetuum mobile. What prevents this magnetic perpetuum mobile from working? I don t say I full ...
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4answers
192 views

Moon causing tides violates conservation of energy?

It is a simple fact that the moon causes tides in the earth. But these tides seem to be a violation of the conservation of energy. Why exactly would this be? Well think of it the way I am thinking ...
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1answer
126 views

$Q$ factor of a pendulum

according to the definition of the Q-factor of damping, it is given by: $Q = 2\pi\frac{Energy \; Stored}{ Energy \;Dissipated \; per \;cycle }$ Q = 1⁄2 --> Critical damping Q > ​1⁄2 --> Over ...
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2answers
44 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 ...
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1answer
65 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
45 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
69 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
67 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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0answers
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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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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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