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Questions tagged [dissipation]

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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
46 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
69 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
57 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
62 views

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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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
47 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
84 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
32 views

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
33 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
60 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
77 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
66 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
113 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 ...
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1answer
73 views

Explanation of a spring using “Artistotle's law of motion”, $\vec{F}=m\vec{v}$

So I was watching Susskind's Classical Mechanics lectures and I didn't understand something in the second lecture. He was telling about Aristotle's Law of motion which is $$\vec F = m\vec v.$$ He ...
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1answer
61 views

Exact form of the damped wave equation

The undamped wave equation has the standard form \begin{equation*} \frac{\partial^2 \psi}{\partial t^2}=c^2\nabla^2\psi \end{equation*} while the damped wave equation is frequenly found written in ...
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2answers
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How much energy is wasted by a noisy refrigerator?

I recently bought a new refrigerator for my kitchen. The feet are adjustable but I've been lazy. Whenever the motor runs and the feet aren't all touching the floor there is a loud buzzing noise. As ...
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1answer
35 views

Potential energy-Conservative forces

Does potential energy exist because conservative forces exist? Can a system of objects that interact with dissipative forces have potential energy?
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Is there an intuitive reason the resistance that maximizes power dissipation in this simple circuit has a simple form?

Consider the following circuit: A textbook problem[2] asks to find the resistance $R$ such that the power dissipated in $R$ is maximized (assuming $R_1$ and $R_2$ are fixed). I found that $R$ should ...
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1answer
31 views

Damped mechanical wave

a string with density $\rho$ and tension $T$ is bound at it's two ends at $x=0$ and $x=L$. there is a force acting on the string proportional to the velocity $F(x,t)= -2\gamma \rho \dot \psi(x,t)$ ...
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3answers
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If the molecular collisions are elastic will there be any dissipation in a fluid?

Viscosity arises due to collisions of the molecules of one layer of a fluid with another in contact. But viscosity is a dissipative element leading to heating and dissipation. Where does it heat come ...
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1answer
86 views

Airflow velocity and volume loss due to friction

I have a vacuum that the manufacturer claims capable of moving 20,000 cfm of air. In my application we often connect 150 feet of 6 inch diameter, smooth bore, flexible tubing to the vacuum. I know ...
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1answer
125 views

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
61 views

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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2answers
105 views

Significance of the complex component in the underdamped harmonic motion equation [closed]

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
38 views

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
120 views

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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4answers
82 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 ...
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2answers
101 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<<\...
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4answers
150 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
255 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
85 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
192 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 ...
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1answer
77 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
129 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 ...
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1answer
478 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. ...
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1answer
29 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
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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
103 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
114 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
96 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 = ...
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4answers
106 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 ...
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1answer
196 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 ...
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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 ...