Energy Definition and 999 Threads

I'm looking for some method to focus a variety of sound frequencies in the environment via metamaterials, parabolic reflectors, Helmholtz resonators, or some sort of device that can somewhat "attract" sound from it's regular path. I've heard about Schumann resonance in the atmosphere and I was...

Question concerns a remark by Dirac in his "General Theory of Relativity", chap. 33, p. 65-66. Dirac is working with plane waves, so the metric $$g_{\mu\nu}(x) = g_{\mu\nu}(l_\sigma x^\sigma)$$ where ##l_\sigma## is the wave vector. Writing ##\xi = l_\sigma x^\sigma##, Dirac defines...

"This is for science" - Dude with the broken nose I do sort of feel bad that I think this is funny. Proof that I am a flawed human being.

The Wikipedia article https://en.wikipedia.org/wiki/Decay_chain has some numbers but fails to provide some sums and specifics I´d prefer. The major natural ones: Uranium series: 238U α 4.26975 4.468×109a 234Th β− 0.273088 24.10 d 234mPa β− 2.268205 1.159 min 234U α 4.8698 2.45×105a 230Th α...

My interpretation of this equation is "how much does the electrical potential energy changes when I move the particle a little bit"? Suppose that I have some arrangement of charges, with Q at x and q at x'. Then I move the charge q a little bit in the direction of Q (dx), it will require some...

P.S. I tried to clean up this post, but the program does not seem to be working correctly. When I click on "preview" I get one thing, but when I go back to my original text, it does not match the preview. I plugged the expressions for mu and omega into the equation for total energy and...

Here is my line of thinking: I know A and B aren't correct since the work done would be negative since the electric force and displacement are in opposite directions. When calculating the electric potential energies to consider options C and D, I thought the initial electric potential energy of...

[ I think I should have asked this many years ago when I was studying !!! However it will help me re-understand thermodynamics and entropy a bit, and may be good for others on the same path so... ] Considering two portions of a liquid. Container A liquid is at a high temperature, container B...

Just for fun, suppose electrical energy had never been developed but technology had continued to advance after Classical Physics was well understood. What do you suppose the technology would look like by now in a fictional alternative timeline?

Pretty much everywhere secondary electron has energy of 50 eV or less. I would like to know bit detail definition of secondary electron in the SEM. Why there is no SE with higher energy even beam energy is quite high like 10KeV and more. What is the difference between secondary electron and...

Hello people, super confused here. In electrostatics we define the work done on a point charge Q to move it from A to B as $$W = Q \cdot \int_A^B \vec{E} \cdot d\vec{s}$$ . Where exactly does the energy go here? For instance when a positive charge Q is moved in the direction of the electric...

The work done by an artificial satellite in an orbit in a day is equal to the total energy produced, utilized and stored by the satellite during that day.

Consider this situation. A mass $$m$$ is dropped onto the spring system from rest , and it is given that the smaller spring gets compressed by a distance $$h$$ My main query in this question is regarding the use of Work Energy theorem, which states that the work done on a body by all the forces...

The NY Times is reporting the discovery of a new ultra-high energy (UHE) neutrino. This is reporting on a paper published in Nature today: https://www.nature.com/articles/d41586-025-00444-1 According to the article, the muon produced by the collision of a cosmic neutrino with a molecule in the...

So Coulomb's law is this simple formula for calculating the force between two charges. Kq1*q2/(r^2) (Disclaimer: I know this computation is not actually possible I was just wondering if it would give the correct result) I was wondering if it is valid to sum the force vector from every charge...

Let's construct a model: a small ball with mass m is thrown on a horizontal plane with a V, and the direction of the velocity makes an angle θ with the horizontal plane. What is the maximum height it can reach? (ignoring air resistance) We that the kinetic energy of an object will not be...

I am interested in a question related to energy for different reference frames. Let's say we have two inertial reference frames A and B. The reference frame B moves relative to the reference frame A at a high speed at which relativistic effects are manifested. In reference frame B there is a...

My try: At first, the energy is ##U_1 = \dfrac {q^2_1}{2C_1}##. After inserting the dielectric and reducing the distance between plates, the capacitance changes to ##\dfrac {5}{2}C_1##, and because the voltage is constant, we have ##q_2 = \dfrac {5}{2}q_1##. When we disconnect it from the...

According to what we can verify and experience among the various questions of modern physics, can we somehow affirm that everything on the planet is made up of energy or matter? Can it somehow be partially affirmed, always aiming at the explanations of modern physics studied until then?

Hi, Unfortunately, I can't quite work out the terms in the task The expression in the integral (4) corresponds to the Lagrangian and since ##t## and ##\varphi## are cyclic variables, the following follows: $$-\frac{d}{dt} \frac{d L}{d \dot{t}}=0 \quad \rightarrow \quad -\frac{d L}{d...

Just floating an idea. H2 production by electrolysis uses a lot of energy particularly as it usually produces oxygen as well. The energy required to produce the oxygen is usually wasted. So, the idea is to have a cell that has a H2 production electrode as normal, but uses an opposite...

So how can I calculate the energy of a volcanic eruption? If I know the VEI, total ejecta, duration and plume height would that be enough or would I need more variables?

My son is in year 7. Please see attached image for more details and context. We don't understand why the answer to the question no 4 is "F" and not "D"? The rollercoaster travelling at the fastest speed..... He put D but the correct answer is F. Please help. Thank you in advance.

https://www.msn.com/en-us/money/other/power-giant-strikes-while-the-iron-is-hot/ar-BB1rfdqS?ocid=msedgntp&pc=NMTS&cvid=773b1fa4940c44f68905bee6c78ee8a7&ei=66

Hello again. I am interested in the possibility of achieving a very high energy density, using accessible technical resources. I refer to the word accessible in terms of technical feasibility, not monetary cost. --------- It all started by thinking about how it would be possible to avoid the...

After collision energy is mgh/2. I am having trouble in writing the energy equation after this.

$$u(\nu, T) = \frac{8 \pi \nu^2}{c^3} \cdot \frac{h \nu}{e^{h \nu / k T} - 1}$$ Now using the relation ##c=\nu \lambda##, $$u(\lambda, T)=8 \pi h \frac{1}{\lambda^3} \cdot \frac{1}{e^{hc / (\lambda k T)} - 1}$$ Now this is still per unit frequency. To get it to per unit wavelength, then $$...

I'm familiar with statics and calculating the force that will start to tip a block (lets call it H). I'm also familiar with when a block will get to the point of tipping over, rather than sitting back down if the load is removed. What I'm not familiar with is how to calculate the duration for...

Researching the Casimir Effect and possibilities of incorporating this energy capture method into nano structures as part of any of diverse machines and systems, was linked here by an ai chat model. I wish to create entities. I am very interested in advancing our grids, states of the art...

Hello there. I have a Master degree in Mechanical Engineering and work on the energy assessment area. But i have a huge interest in subjects like General Relativity, particle physics, Cosmology and Astronomy.

Dear all I have the following problem with my working attached as a PDF. I want to calculate how far particle a travels after the string has snapped. The question says the particle A travel for 1m before the string snaps. The question asks me to use energy methods to do this. The total distance...

By definition, we have that ##G=H-TS##, which means that ##dG=dU+PdV+VdP-TdS-SdT##, and at constant temperature and pressure, ##dG=dU+PdV-TdS##. As ##dU=TdS-PdV##, I asked my lecturer why ##dG=0## isn't true for all processes at constant temperature and pressure. He then tells me that there is...

I have 2 questions, the first has been asked (unfortunately not directly answered) below: https://electronics.stackexchange.com/questions/199977/loaded-q-factor-of-parallel-rlc-with-series-resistive-load I have reposted the question below for ease of reference. For the given circuit...

Hello Universe, I am Benjamin (Ben) I am new to this forum. At first, I will just be nosey and read through the post to get a feel for the environment. I am open for any discussion about any subject. I keep an open mind about everything. Here are a few areas of interest I have but not limited...

I still don't get this and most answers all over kind of miss the point and just kind of recite without really explaining. Here's the dilemma. Yes, kinetic energy grows exponentially with speed. So a 1kg object changing from 0 to 1m/s increases by .5J. And from 4 to 5m/s increases from 8J to...

Included a diagram as well... forgive me... I cannot seem to 'uninvert' the attached picture final velocity is zero if we set the lowest point that the mass reaches as zero, then the final height is zero let H be the 'extra' length that the spring reaches over and above the initial stretch...

Hi I have a problem with task c) For the Poynting vector ##\vec S## and the energy density ##\omega## I got the following: $$\vec S= \frac{1}{\mu_0} \frac{4 I_0^2}{c \varrho} \frac{t}{c^2 t^2 - \varrho^2} \Theta(ct-\varrho)^2 \vec{e}_\varrho$$ $$\omega= \frac{1}{2} \epsilon_0 \frac{4 I_0^2...

[Mentor Note: Two threads on the same basic subject have been merged into this one thread.] Dear PF Forum, It's been a long time since I logged in PF, and I hope everybody is in a good health. Recently I'd like to know what is Kardashev scale type II and III I mean, Type 1: All energy from...

TL;DR Summary: I've done a torque calculation but as I'm new to this I would appreciate if someone could confirm my answer so I know I'm doing it right. The energy it would take to rotate a 10 mm cube weighting 7.5 grams 180 degrees in 0.001 seconds. To simplify it I didn't include drag or...

How to calculate the kinetic energy of an object propelled by a magnetic field. For example I have 2 magnets face to face in opposition. Each magnet is a N42 Neodymium cube dimensions 10, 10, 10 mm they are in free space with no interference. The maximum pull strength is 4.7 kg. If I were to...

Using the above equations and the given information, I get ##k=2.48*10^-4## 2.47∗10−4max=7.56∗10−5##Vmax=7.58*10^-5## and ##total energy=8*10^-6 joules##. My answer is clearly the wrong order of magnitude. The book answer key says 400 joules. My calculation for total energy was...

Observational Assessment of Changes in Earth’s Energy Imbalance Since 2000: 2024 Added greenhouse gases are supposed to be decreasing the OLR.

Could the rotation of tires be used to generate electricity and lengthen range?

i just watched this: and now im wondering, jsut as when the atom bomb converts mass into energy and we can measure it in force and heat and electromagnetic radiation of various wavelengths, obviously just grams, but of what? what particle would we say is representing the 99% of a proton's...

In statistical physics, in a two level system, I'll give an example to show what I am talking about: situation 1) energy 0 and energy E situation 2) energy E/2 and energy -E/2 Are these two situations equivalent? Computing the partition function for both of them it seems they are different...

My thinking is that because of the law of conservation of energy, the amount of energy needed to raise an object to a certain altitude has to be at least as much as the amount of energy released by the object if it were to be dropped from that altitude and hit the ground (and all that released...

Hello All, I have some space outside my room which have sunlight all day. The room heats up to very high temperature. Is there any way I could use that heat to cool down my room without using solar panels? Just a thought.

TL;DR Summary: Need some sources for Lagrangian and Hamilton Mechanics. I was looking through some of my physics books, and in one chapter they mentioned Hamiltonian and Lagrangian Mechanics, I thought it seemed pretty useful and looked into it some more. I noticed that these mechanics were...

Physics describes energy in various forms and each with an appropriate unit of measure. I am curious as to what can be said about the 'form' of energy in the universe's first seconds. Online references locate the Big Bang singularity at an estimated 13.787±0.020 billion years ago with the...

I asked Chat GPT this but could'nt get a satisfactory answer. I felt he was making it up as he went along. In principle it should be possible to set up two lasers emitting the same frequency and synchronize them so they are perfectly out of phase so that both beams destructively interfere. I...