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3answers
125 views

Diffuse laser light in a surface

Im building a laser target. It consists of a box, with a black plexiglass circle in the center of one of its sides, and a larger white circle around it. The black for the inside shots, and the white ...
5
votes
2answers
685 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic ...
3
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1answer
80 views

Intuitive explanation for subsonic Fanno flow

In most situations in physics, the effect of kinetic friction is to reduce the macroscopic kinetic energy of a system and convert it into heat, thereby increasing its temperature. but in the case of ...
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1answer
43 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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1answer
52 views

What is the difference between damping and friction?

What is the difference between damping and friction? Both of them slows down any moving system. So whats the conceptual difference between them?
3
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0answers
62 views

Liouville's theorem for systems with dissipation described by a single hamiltonian

Following this link, one can treat dissipation in the lagrangian by using a factor $e^{\frac{t \beta}{ m}}$ in addition to the Lagrangian $L_0$ of a system without disspation: $ L_0[q, \dot{q}] = ...
2
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0answers
62 views

Wronskian of complex second order linear differential equation

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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0answers
66 views

Quantization of non-variational 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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0answers
130 views

Friction in Lagrangian formulation

We know the Lagrange equations are: $$\frac{\partial \mathcal{L}}{\partial q_i}-\frac{d}{dt}\left(\frac{\partial \mathcal{L}}{\partial \dot{q_i}}\right)=0.$$ Then, when we add friction in there, we ...
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0answers
29 views

How is Thermal Design Power (TDP) related to Surface Power Density (SPD)

Although this question is kind of IT related I'm interested into the actual physical backgrounds and thus posting it here. I know that TDP is an indicator for dimension of the thermal dissipation ...
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0answers
63 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?