Energy Definition and 999 Threads

I am wondering if it is possible to calculate either the Kinetic Energy or Rotational Kinetic Energy of an object if we have the Power (kW), Torque (Nm), and Speed (RPM) of the object.

Hi, I am trying to get to an answer for the following scenario. Imagine you have an electrochemical cell in its most basic terms. On the negative electrode you have 3 moles of iron metal in a chloride solution. On the positive side you have 3 moles FeCl3 solution. These are separated by a...

Let ##U## be a bounded open subset of ##\mathbb{R}^n##. Given a continuous function ##\phi : \overline{U} \to \mathbb{R}##, show that any real-valued function ##u## of class ##C^2(\overline{U})## such that ##\Delta u = \phi## in ##U## and ##u|_{\partial U} = 0## is a minimizer of the energy...

krotovs solution is based on energy conservation. My question is that why the solution didn't consider inductors energy? the question: The solution:

Hi, I completely failed this homework. I mean I think I know what happen, but I don't know how to show it mathematically. The energy lost by the wave is used to oscillate the electrons inside the conductor. Thus, the electrons acts like some damped driven oscillators. I guess I have to find...

Here, I have assumed very quick movement of the moving part. So, as per the mmf-flux curve, flux linking with the system will be unchanged during the movement. To support this assumption, I have made use of the following analysis. In this graph, the movement of the part happens quickly (small...

Summary: I am looking for suggestions on an informative read surrounding nuclear energy I am a junior year physics student at UCSB looking to go to grad school for nuclear physics and eventually work with nuclear energy. My curriculum at UCSB does not offer any explicit classes surrounding...

Hi, I have hard time to really understand what's a stationary state for a wave function. I know in a stationary state all observables are independent of time, but is the energy fix? Is the particle has some momentum? If a wave function oscillates between multiple energies does it means that the...

This is just a curiosity to me. My interest is from the position of a layman (as you will see from my description below). In the double slit experiment it shows a wave passing through both slits and interfering with itself to create an interference pattern. This is how I understand it... From...

A screenshot from a book which describes it: So I am trying to picture this one: 1. A laser is "pumped" through a cylinder made from lithium niobate which is placed at 90 degrees, perpendicularly...so that the laser passes through the body of the cylinder (and not through the 2 round ends)...

So, I use Ansys (well known FEM software) and get the next output for a modal analysis toy problem (If you happen to know Ansys that's a pre, but I promise it shouldn't matter). The problem is a simple beam, clamped at one end. I used 160 20-node brick elements to solve it (so no Timoshenko...

Could kinetic energy possibly depend explicitly on time in the lagrangian for some arbitrary set of generalized coordinates?

Is there a way to know what is the amount of energy a wire can transport and know what is the amount of energy transported by moving air at a certain psi.

I found a paper (https://arxiv.org/pdf/astro-ph/0411299.pdf) which talks about quantum systems emitting energy due to spacetime expansion. Is this true or only a hypothesis?

The book(Schaum) says the above is the solution but after two hours of tedious checking and rechecking I get 2n^2 in place or the 3n^2. Am I missing something or is this just a typo?

Hello I am a physiology student who is curious about the physics underyling blood flow and pressure. I have taken physics classes however at the elementary level the focus is on ideal fluids in systems with no friction. I would appreciate any answers or if you could point me in the right...

what is the reason for that the energy hypersurfaces in a phase space, which belong to systems with constant energy are closed? ( see picture )

I'm thinking about how the energy is conserved when a E.M. wave pass through a conductor. If a E.M. pass through a conductor, the electrons must move "oscillated", thus the energy from the E.M. wave is converted to kinematic energy. Another way I see that is the E.M wave must generate a current...

I found an old article (https://journals.aps.org/pr/abstract/10.1103/PhysRev.137.B1379) which talks about conservation of energy in an expanding space. Apparently, the author found that energy is conserved at local scales (like the motion of planets in our solar system) as one would expect, but...

Assume two observers very far from each other, so far, that the accelerating expansion of the universe matters. (edit: But not outside of each others event horizons.) They will send light beams each other, and measure the energy of it. Also tie them together with a very long rope to fix their...

I was reading this interesting article [1] which talks about particle production in an expanding universe. Usually this process is proposed to have occurred in the early universe, when the expansion was in the inflationary phase and it was so powerful that matter was created in particle...

Earlier today, I posted a question about the strain energy function. I am happy with the answer (I love this group). But the answer opened up a deeper question. Many elasticity textbook posit the existence of a strain energy function: And they make an additional assumption about its...

(If this is in the wrong forum, please move it) Here is the potential energy of a spring Here is the strain energy function in elasticity The look alike -- I like that. If we want the force in the spring, we take the derivative of V with respect to the displacement and make the result...

When an n-type material comes in contact with a p-type material to form pn-junction, electrons with the highest energy in the conduction band will diffuse to the p-side to reach equilibrium so the entire band structure on n-side will shift down relative to p-side as described in the following...

Hi, everyone! There are a lot of work energy conservation laws and I get confused which one of them summarizes all of them. Which one I should keep with me and rest should be easy to derive on spot ? 1. ##\Delta E_{mec}=0## 2. ##\Delta E_{mec}=W_{ext}## 3.##\Delta E_{mec} + \Delta...

I am working on a sanity check for capacity vs load and if anyone here has experience with off-grid solar, any feedback would be much appreciated. The application is to run a fridge and a modem off-grid on a piece of land in New Mexico. I read that in December (worst case month) the area gets...

Apologies for an additional thread (could not delete the previous one which was not coherent). After reading this paper: https://link.springer.com/article/10.1007/s10701-021-00464-7 "Fast Vacuum Fluctuations and the Emergence of Quantum Mechanics" Gerard ’t Hooft I was struck by a general...

Hello, I'm hoping someone can help me understand a statement in Sakurai Modern Quantum Mechanics (3rd edition). In particular, in the section that describes free particle in infinite spherical well (page 198, section 3.7.2), after the text has shown that for a given ##l## value, the energy...

We are all familiar with ladder operators, such as QM harmonic oscillators or in QFT to produce energy states which are interpreted as particles. But when a creation operator raises the energy level of a system, where does that energy come from?

From this post-gradient energy in classical field theory, one identifies the term ##E\equiv\frac{1}{2}\left(\partial_x\phi\right)^2## as the gradient energy which can be interpreted as elastic potential energy. Can one then say that $$F\equiv -\frac{\partial...

There is an article written by astrophysicist Edward Harrison [1] which defends that energy could be extracted from attaching an imaginary cosmologically long string to a receding object from us in an expanding universe. He says that the energy extracted is potentially limited (in decelerating...

Energy = ##\frac{2000}{235}## x 6.02 x 1023 x 0.7% x 200 x 1 x 106 x 1.6 x 10-19 = 1.15 x 1012 J But the answer is 1.15 x 109 J I am off by a factor of 1000. Where is my mistake? Thanks

I was reading an article by Edward Harrison, which tackles the problems of conservation of energy at cosmological scales. At some point (point 2.4) he cites several article, including one by Rees and Gott, which he says indicates that the internal energy of a comoving volume (e.g. a cosmic...

It takes energy to compress an ideal gas, and that same amount of energy is output as heat. But we also gain the potential energy of the compressed gas. It seems to me that we are doubling up our energy. Can anybody explain in simple, practical terms (to a humble mech engineer) how this works...

If I start with two, otherwise isolated, masses M and m initially together and do work to separate them then the work done, I assume, goes into the gravitational binding energy between them. Will the system of mass M and m have increased in mass due to this in accordance with e=mc^2? I...

Sean Carroll has an article (https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/) where he explains that matter can gain energy from spacetime expansion. At the end of the article, he says: In general relativity spacetime can give energy to matter, or absorb it from...

This is in fact a shamelessly simple question to a point the reason it puzzles me is because it's too simple: So basically you have a closed empty/hollow cylinder filled with either gas or even an ordinary solid ball...and then on the left side of the cylinder you put a force on the "fuel"...

This is my answer: $$KE_{total}=KE_{centermass}+KE_{uppermass}+KE_{bottommass}$$ $$KE_{total} = \frac 1 2 (mv^2 + 2m(\vec {v} + \vec {wL})^2) $$ But, the solution manual says that the answer is this: $$KE_{total} = \frac 1 2 (mv^2 + 2m(v^2+w^2L^2)) $$ I think he regard this composite body as...

Im not really sure how to answer this question. Would you have any ideas?

Q=Qwarm water+Qsteam Q=mct+mLv Q=(8kg)(4200J)(100C-25C)+(2kg)(2.3*10 to the power of 6 J/Kg) Q=7.12*10 to the power of 6 J Is this the correct answer?

This is not homework, just a question of curiosity. Something that came to my mind last night. Say I have a magnet and a piece of iron. Say I use it to do weight training exercise. I stick the magnet on the wall and stick the iron on the magnet. Say it takes 100lbs of force to pull the piece of...

Firstly, what I'm about to do is to find the velocity of the mass soon after it doesn't touch the slide A anymore. using momentum conservation, I got ##0 = mv' + MV'## with ##v'## and ##V'## are the velocity for mass C and slide A respectively immediately after they lost interaction. Now, I...

Hey all, I am working through some practice problems and am stuck at the following one: "A cylindrical tank 10m high has an internal diameter of 4m. How much work would be required to fill the tank with water if the water were pumped in i.) at the bottom and ii.) over the top edge?" Part i is...

What is the free energy and why is it so important? I realize there's different types but what is the underlying concept? Is a general principle of CM systems to attempt to minimise free energy?

Me again! For a sci-fi story I'm working on, I've created a sci-fi technology called an Aneutronic Triple Alpha Fusion Reactor. It works via aneutronic fusion, in this case, fusing Deuterium with Helium 3, but it also mimics the triple alpha process found within stars to maximise fuel use...

Suppose there is a pressurized gas canister in space, at rest. With a mass "m" of gas inside of it at a pressure "P". Next the valve of the canister is opened. The canister will accelerate in the opposite direction to the valve opening. When all the gas has left the canister, it will be moving...

About a year ago, I heard Leonard Susskind discussing how entangled black holes could create spacetime. As I was listening to Prof. Susskind describe the mechanisms for creating entangled black holes, and how these black holes might create their own spacetime, it occurred to me that if we were...

The energy of an electromagnetic wave does not depend on the frequency of the wave, only on the amplitude. Then why is light with higher frequency more energetic than light with lower frequency?

I already know the solution to this, all you do is set the height of the top of the trampoline to 0 and solve for initial velocity so the equation for the conservation of energy $$mgh_0 + \frac{1}{2}mv_0^2 + \frac{1}{2}kx_0^2 = mgh_1 + \frac{1}{2}mv_1^2 + \frac{1}{2}kx_1^2$$ becomes...

Hello! For the experiment I am working on we are using as the ion source an ablation target. We have a 1 inch coin of the material of interest (ytterbium currently) and we send laser pulses to it (we are using a 532 Nd:YAG laser). Can someone point me towards a paper (or tell me from their...