Questions tagged [dissipation]
The dissipation tag has no usage guidance.
542 questions
0
votes
0
answers
22
views
How to (coarsely) estimate turbulent kinetic energy (TKE) dissipation in a large tank?
I'm wondering if it is possible to say something semi-quantitative (approximate order of magnitude) about turbulent kinetic energy (TKE) dissipation in a large tank of water (6 m tall, 3 m wide). The ...
- 111
1
vote
2
answers
68
views
Doubt with Heat and Potential Energy. (Warning: Many Assumptions) [closed]
I had a question in my Textbook which reads as follows,
Before that, we have to assume that the flowing water is ideal.
So, here we have to equate Change in Potential Energy to Heat Energy/Internal ...
1
vote
4
answers
165
views
Can a stable energy system be created using variable capacitors to generate high current for energy recovery?
My idea is:
If two charged capacitors are connected in parallel so that their positive plates are connected together and their negative plates are connected together. Then, if the capacity of one of ...
2
votes
1
answer
99
views
Variable Doubling in Lagrangian Mechanics
I have been looking into how we handle non-conservative forces in Lagrangian mechanics. They don't form a potential $V$ quite as easily as conservative forces do. I have read in several places that ...
- 51.7k
1
vote
0
answers
38
views
The form of Euler-Lagrange equation $f''(t)+2\lambda f'(t)+\omega ^2 f(t)=0$ [duplicate]
Proof that differential equation $f''(t)+2\lambda f'(t)+\omega ^2 f(t)=0$ when $\lambda\neq0$ is not an Euler-Lagrange equation.
The damped harmonic oscillator equation with a dissipative force ...
- 11
1
vote
1
answer
71
views
Decay Rates of Harmonics in Standing Waves on a String
In my class experiment on standing waves on a string, I used the FFT mode of an oscilloscope to analyze the frequencies produced by the string. I observed that the fundamental frequency exhibited the ...
- 51
0
votes
1
answer
34
views
Rayleigh dissipation function for quadratic drag
Is there a way to adapt the Rayleigh dissipation function to be used for quadratic drag instead of linear drag? I was thinking that something like
$$\mathcal R = \frac{1}{3}(c_d)(v)^3$$
where $c_d$ is ...
- 56
1
vote
1
answer
42
views
The Usage of non Non-Constraint Forces and the Rayleigh dissipation function in the generalized Lagrange equation
The most general Lagrange equation for classical mechanics systems is of the form:
$$\frac{d}{dt} \left( \frac{\partial \mathcal{L}}{\partial \dot{q}_i} \right) - \frac{\partial \mathcal{L}}{\partial ...
- 904
0
votes
3
answers
52
views
If there is not energy loss will a circuit board do the same processes forever with the initial energy?
same as above. if we for example take a circuit board of laptop without any speakers or screen just the circuit board and if we can stop energy loss from this can it do the same process forever with ...
0
votes
0
answers
33
views
Lagrangian in systems with damping
The top comment of this post (Difficulties while trying to apply the Lagrangian approach to a problem with damping) mentions the importance of multiplying the standard lagrangian with $e^{\omega t}$ ...
- 56
1
vote
1
answer
67
views
Lagrangian Formulation in Non-Conservative Systems
I am working in a non-conservative system. Would it make a difference if I
Formulate the Lagrange Equation with an additional term on the right hand side of the equation to account for the Rayleigh ...
- 56
3
votes
1
answer
131
views
Why do systems with greater energy fluctuation have better heat dissipation ability?
In canonical ensemble ($NVT$), it can be shown that the fluctuations in energy is related to the specific heat of the system according to the formula,
$$
\left( \Delta E \right)^2 = k_B T^2 C_V
$$
...
- 3,134
33
votes
13
answers
5k
views
How is it possible to know a proposed perpetual motion machine won't work without even looking at it?
It is often said that perpetual motion is impossible. Many people try to invent perpetual motion machines. Apparently every such attempt is doomed to failure. People don't even need to look at one to ...
- 45.6k
0
votes
0
answers
21
views
Can a thermistor's heat capacity be calculated using the still air thermal time constant and dissipation constant? (using $C = τ·h·A$)
Thermistor data sheets typically state the thermal time constant in still air and the dissipation constant in still air.
For a body heating or cooling, the thermal time constant can be calculated as $\...
- 113
0
votes
0
answers
22
views
Does a thermistor's dissipation constant also apply to cooling when current stops? How is it connected to the thermal time constant?
If a thermistor has a dissipation constant of, for example, 0.5 mW/°C, then it is expected that dissipating 5 mW in the thermistor will raise the temperature 10°C above ambient. At that point the ...
- 113
1
vote
4
answers
90
views
Example of a system which has both rheonomic and conservative constraint?
Generally speaking, rheonomic constraints are dissipative, although there are exceptions.
This was given in classical Mechanics by Rana and Joag
So, I was wondering what are those exceptions. If ...
- 13
5
votes
1
answer
343
views
Mathematical proof that viscous damping always diminishes energy
In S. Coleman's The Fate Of the False Vacuum I he imagines a particle in a negative potential with "Euclidean" Lagrangian:
$$ \frac{1}{2} \left(\frac{d \phi}{d \rho}\right)^2 + U$$
after ...
- 179
2
votes
2
answers
233
views
Validity of $\mbox{d}H/\mbox{d}t=\partial H/\partial t$ for dissipative systems
It' well known that in Hamiltonian formalism one has
$$
\frac{\mbox{d}H}{\mbox{d}t} = \frac{\partial H}{\partial t}.\tag{*}
$$
One proof can be found here. Therefore, the total change of energy during ...
- 717
1
vote
1
answer
52
views
Can an optical medium be lossless and dispersive?
Occasionally, I come across the phrase "lossless dispersive linear optical medium". How can such a medium be possible mathematically? I mean the real and imaginary parts of the electric ...
- 483
5
votes
1
answer
178
views
Would the Moon move away if the Earth were frozen with no liquid tide?
The moon is moving further from the Earth. To the extent that after 600 million years we will no longer enjoy full solar eclipses as it will be too far away to completely block the sun.
The reason the ...
- 151
1
vote
0
answers
24
views
Output of ventilator and air friction
Imagine you have a ventilator with straight rectangular ventilator blades which are rotated at some small angle from a perpendicular line to the rotating axis. The ventilator has 100% efficiency (all ...
- 11
1
vote
2
answers
47
views
Why exactly (on the level of particles interacting with each other) do things heat up with friction? E.g. airplane from friction with air
Why exactly (on the level of particles interacting with each other) do things heat up with friction? E.g. airplane from friction with air. Also what is the difference between conduction and convection,...
- 25
0
votes
3
answers
95
views
Does a single ball undergoing ideal simple harmonic motion count as being in thermodynamic equilibrium?
(Posting this and deleting a previous similar post to make the question more clear.)
Suppose we have an isolated system inside a box consisting of a spring and a ball attached to the spring. The ball ...
- 8,776
0
votes
0
answers
28
views
Damping of a Lagrangian System in 3D [duplicate]
I have a Lagrangian, that describes a Pendulum hanging on a spinning disk in 3D. It looks like this:
$$
L(p,\lambda, t) = \frac 12m\|\dot p\|^2-m g p\cdot\hat k+\lambda(\|p-q\|^2-l^2)
$$
with $p$ and $...
- 79
2
votes
1
answer
54
views
How to demonstrate in a simple way that this system of differential equations form a damped harmonic oscillator? [closed]
How may I demonstrate in the most simple way that the following system of differential equation form a damped harmonic oscillator ?
$$
\dot x = -\alpha_x x - \omega y \\
\dot y = -\alpha_y y + \omega ...
- 123
3
votes
1
answer
128
views
Information Loss in Chaos Theory
Is it accurate to suggest that in chaos theory, information is in practice lost due to the impossibility of characterizing the system's state with infinite precision, making it unfeasible to run the ...
- 352
18
votes
3
answers
3k
views
Rocket attached to a pendulum. How is energy conserved?
I'm trying to wrap my head around a conceptual problem involving a simple pendulum with a rocket attached to its mass. Imagine the rocket expels gas to provide a tangential thrust force. However, the ...
- 183
6
votes
2
answers
759
views
When the energy in a conductor is not carried by the electrons, how resistances warm up?
The energy flux in a conductor paints the picture that the "collisions" of the electrons with atoms (Drude Model) are not the reason for an resistance warming up in the presence of an ...
- 351
0
votes
0
answers
22
views
Rotating disc with viscous damping with large initial angle (always 90 degrees) (unbalance/instability)
I have an application for a rotating disc with inertia that is put on a "knife edge" balancing fixture. The disc is then released in order to find the "heavy spot", once identified ...
0
votes
2
answers
124
views
Where does a body get its energy to heat up when falling from height $h$?
When a body falls from a height $h$ it loses some energy to the surroundings, is it the energy that is lost to the surroundings that increases its temperature on the remaining energy that is stored in ...
- 1
0
votes
0
answers
56
views
Energy loss due to Cherenkov radiation
I'm trying to find a formula for (or some sort of direction towards approximating) the energy lost by a ultra relativistic positron when traveling through a cherenkov detector but I can't seem to find ...
- 1
0
votes
2
answers
106
views
Heat as a path dependent integral
Heat can be considered as an inexact differential. Hence, we could conclude that:
there exists a path $\gamma$,such that:
$$
\oint\delta Q \ne 0
$$
Hence, $\int\delta Q\ne\Delta Q$.
i.e. $\Delta Q$ ...
1
vote
1
answer
105
views
Direct conversion of potential energy into heat
Is it possible for potential energy to be dissipated (converted into heat) without being first converted into kinetic energy? Put differently, are there isolated systems at complete rest which turn ...
- 205
1
vote
2
answers
81
views
Accelerating car under the influence of rolling friction
Consider the following textbook problem:
An electric car of mass $m = 3500 kg$ has stored $E = 100 kWh$ in its battery. The rolling resistance coefficient is $\mu_R = 0.8$. How far can the car travel ...
- 205
0
votes
5
answers
148
views
Energy and Non-conservative forces
I understand that one cannot assign a potential energy to all points in space in the presence of a non-conservative force field due to the work done by the force being dependent on the path taken. ...
- 145
0
votes
1
answer
118
views
Where does the energy go in inelastic collisions?
Chabay and Sherwood write in Matter and Interactions on page 406 about sticking collisions:
We'll consider an inelastic collision in which a truck and a car collide in an icy intersection and stick ...
- 1,810
-1
votes
2
answers
97
views
What’s wrong with this idea for an energy generator? [closed]
Okay I know a perpetuum mobile is impossible, so I think this should be wrong.
I thought about heat pumps with a COP of 3.5, which is like 350% efficiency compared to a simple electrical resistor. Now ...
- 113
2
votes
1
answer
75
views
Modeling a viscoelastic string with a collection of damped spring oscillators? (To replace finite difference model.) How to find $Q$ per harmonic?
Background
I have simulated a vibrating viscoelastic string fixed at each end under tension using finite difference modeling. Most simply this can be done using Kelvin-Voigt style mass-spring dampers ...
- 343
2
votes
0
answers
75
views
Vibrating string and damping
Suppose we have a string (in tension) with its ends fixed. Think of a guitar string. Suppose we start with a plucked initial position and we let the string free. If we use the wave equation: $u_{tt}=c^...
- 242
1
vote
1
answer
90
views
When does exponentially damping term in Lagrangian make physical sense
I have a question on adding dissipation into the Lagrangian. On this page:
https://profoundphysics.com/friction-in-lagrangian-mechanics/ the approach with adding an exponential factor to the ...
- 113
-1
votes
1
answer
37
views
Continuity Equation on a Non-Ideal System
I recently watched a video on the diffusion equation for neutrons in a fissile material, and at about 2:30 minutes into the video, the author points out that the right hand side of the continuity ...
- 11
3
votes
1
answer
171
views
Infinite reflection inside a glass loop
If you had a loop made of completely transparent glass (or other material), in the shape of a donut; think atomic collider (but probably not needing to be so large :) ), and you introduced light from ...
4
votes
1
answer
513
views
Sloshing water coming to rest?
Something I've noticed is that when I jostle a glass of water, the water inside will start sloshing back and forth. Gradually, the water comes to rest. However, if I move the glass (i.e., translate it)...
- 153
0
votes
0
answers
30
views
Asymmetry when $t\rightarrow -t$ [duplicate]
If we consider the equation of critical damping $$x=(a+bt)e^{-ct}$$
then the graph is
However, it is asymmetric for positive and negative time values. I have an intuition that this should be the case ...
1
vote
3
answers
71
views
The lowering of a block using a spring and the net work done by each force involved
A spring hangs vertically in its relaxed state. A block of mass m is attached to the
spring, but the block is held in place so that the spring at first does not stretch. Now the hand holding the block ...
0
votes
0
answers
89
views
Solutions to critically damped harmonic oscillator?
From MITOpenCourseWare, I was learning about the damped harmonic oscillator. Some context is pasted below.
Case (iii) Critical Damping (repeated real roots)
If $b^2 = 4mk$ then the term under the ...
- 49
-4
votes
1
answer
82
views
Could a perpetual motion machine be made using a filling buoyant object that sinks when filled and releases when bottoming out? [duplicate]
Could you make a perpetual motion machine via buoyancy? If you started with 2 types of fluids with different buoyancy. Then add a buoyant object capable of filling with the top fluid where it closes ...
-1
votes
1
answer
85
views
Can you generate more heat than the amount of work done? [closed]
I have doubt regarding how can COP of a refrigerator can be one!
It can happen only when heat is more extracted when work inputed or rate of heat absorbed is more than power? Can any one of the reason ...
0
votes
3
answers
133
views
Perpetuum mobile working in vacuum
Can a perpetuum mobile work in a vacuum? I think when it is in vacuum it won’t stop working because of outside forces, because there is no outside forces. Tell me if I’m wrong.
0
votes
1
answer
150
views
Energy dissipation derivation with friction in Lagrangian context
I am self-studying analytical mechanics, and I am stuck in an intermediate derivation of the equation for energy dissipation in a Lagrangian context.
Frictional forces cannot be derived from any ...
- 95