Energy Definition and 999 Threads

I am a student at high school who just finished a paper about nuclear energy and I really learned a lot from it. I found the topic interesting and really enjoyed learning about it. I now am searching out more people who know about it and as much information as I can fins while having good...

Inertia I = 2/5 mr² m=5.98* 10^24 kg. r=6.38* 10^6 kg. I= 9,736 * 10^37 kg. Earth rotation is V= (2 * pi* R)/T = (2*pi*6.38*10^6m)/(24*3600s)=463 m/s angular velocity w= V/r =463m/s/(6.38*10^6m)=7.27*10^-5 rad/s Enerrgy, E= 0.5* I*w²=2.57*10^29 j I get the...

In a globally hyperbolic spacetime you have a global time ##t: M \longrightarrow \mathbf{R}## which foliates it into Cauchy surfaces ##\Sigma_t## and the metric can be written ##\mathrm{d}s^2 = -N^2 \mathrm{d}t^2 + h_{ij}(\mathrm{d}x^i + N^i \mathrm{d}t)(\mathrm{d}x^j + N^j \mathrm{d}t)##. By...

Hi guys, a special relativity problem requested to choose the right graph representing relativistic momentum ##p## as a function of rel. kinetic energy ##K##, from these four: At first, I tried writing ##p## as a function of ##K##, in order to then analyze the function's graph and see if it...

Hello everyone, I am sorry if this question looks silly but my tutor has not replied yet and I need to work it out as soon as I can. Could someone tell me if they see any difference question 1 and question 2? Because I genuinely don't and it is driving me crazy. The assignment is about a coal...

As we know Energy is a scalar quantity. So when we add kinetic and potential energy to get Total energy. So addicting these two energy (kinetic and potential) comes under Scalar addition ? I just wanted to confirm it.

I have no idea how to do this. I've tried conservation of mechanical energy and it didn't work. Ek = Kinetic Energy R = horizontal range of the ball h = height from which the ball is released

So it seems the typical way to approach this problem is to consider the sphere when it has charge q and radius r. With uniform charge density ##\rho##, this becomes ##q = 4/3 \pi r^3 \rho## and so ##dq = 4 \pi r^2 dr \rho##. Using our expression for the potential outside of the sphere, we find...

We have a question about highly energized beta particles (6 to 22 MeV). Is it possible fore this radiation to affect the nucleus of an isotope and not just ionize it? In our case a copper-65 and copper- 63 isotope become their unstable neighbors Cu-64 and Cu-62 due to the high beta radiation...

VR = IR = 400 [ 29*10^-6 * 800 * 10^3 ] = 9280 P = IV = 400*9280 = 3.7 MW I was able to calculate the correct answer from the above, but why can't I use the equation P= V^2 / R?

In an article published in Scientific American, authors Adam Riess and Mario Livio wrote: Why negative pressure? I would think the pressure would be positive, thus making gravity repulsive.

I had found what U(x) was equal to already by plugging in the wave function and simplifying, which is (2h^2/mL^4)(x^2 - 3L^2/2) by the way. But the solution key that I have goes an extra step. After stating the equation of U(x) that I got, it says that: "U(x) is a parabola centred at x = 0 with...

D is correct, the reasoning is as follows: 1/2*(M1V1)^2 + 1/2*(M2V2)^2 = 1/2 * (M1 + M2) (Vcm)^2, since V1 =V2 =Vcm KE retained = KE final = 1/2 *M(Vcm)^2 Let me know if reasoning is okay? However, why A isn't correct?

I am trying to understand the scalar form of the Einstein field equations. I know that you can contract the stress-energy tensor using the metric. And for a perfect fluid model, this turns out to be the energy density summed with the pressure. This also gives the Ricci scalar. However, you can...

So always in my problems i had mass (M) but now i don't and it seems impossible to solve this problem if I don't have mass I think i am missing something. I was looking for similar problems in my book and internet and didn't find any.

Can energy be defined as an entity? The ability to do work is abstract, so is E=mc^2. It seems like energy is a catch-all phrase for something we can only describe in terms of other physical realities.

Energy is equal to Planck’s constant times the number of waves in 1 sec. The time scale for electronic excitation is far shorter then one second. So when we talk about the excitation of an electron from a lower level to a higher level occurring at a certain energy, are we talking about the...

Hello guys, I am designing a 1052 kwh solar farm with 2844 panels in Wales. These panels have to supply energy to a train station but I get minors coverage of the energy required if I do the following calculation which is based on the average sunshine of hours per month. What do you think about...

Hello everyone, I have found this on internet but I don't get the calculations. Can someone do the calculations and show me that the annual consumption is 600 kWh is you use a 200 Wh computer for 8 hours?: A complete desktop uses an average of 200 Watt hours (Wh). This is the sum of the average...

I understand the idea of a fictitious force. What I am confused about is the energy/potential associated with it. For example, if a cylinder of water is rotating, there apparently exists this centrifugal potential energy, which is obtained by integrating mrw^2 dr. Why is it that the...

I have some doubts with respect on how the functional derivative for the kinetic energy in density functional theory is obtained. I have been looking at this article in wikipedia: https://en.wikipedia.org/wiki/Functional_derivative In particular, I'm interested in how to get the...

I was thinking about the Gravity-B probe and the rotation of the satellite due to the Lense-Thirring effect. I was imagining that the satellite, once in orbit, was aligned to a distant star using retro rockets effectively rendering it non-rotating relative to that star. That being said, once...

I've been researching pem electrolyzers, but still don't understand how to mathematically express how platinum reduces the activation energy necessary to dissociate H2O. I've seen the Arrhenius equation solved before, but didn't understand how to get the values for it. Here are the operating...

Hi, I have to find the magnetic energy inside a coaxial cable of inner radius ##a## and outer radium ##b##, ##I = I## By using Ampere's law if ##r<a## ##B = \frac{\mu_0Ir}{2\pi a^2}## if ##a<r<b## ##B = \frac{\mu_0I}{2\pi r}## if ##r>b## ##B = 0## Then, the energy in a magnetic field ##E_b...

Of potential and kinetic energy in their various forms, in their own reference frames, which involve motion? Heat, light, nuclear, kinetic, etc., seem to involve motion. Does potential energy, in any way whatsoever, involve motion? Thermal does. Does nuclear energy involve motion? Seems to...

I have completed part a, from which I got the expression: Cv = 3KTn/(T_f) For part b, the first term is the electron contribution and the second term is the phonon contribution. I'm stuck on how to estimate the fermi energy for the potassium metal. I'm thinking I only need to consider the...

Hello! I've come across this forum looking for an answer to an odd question related to energy production. I have no intention of creating infinite energy so don't worry. Imagine a very strong balloon with a cord wrapped tightly around it. The balloon expands pulling the cord which spins a...

Textbooks always give an explanation for why electrons move between energy levels in atoms with an explanation something like this: 'An electron can jump to a higher energy level if it absorb's energy which exactly matches the difference between final and initial energy level'. My question...

Well, internal energy is the sum of the kinetic and potential energies of all the molecules within a given mass of a substance; this energy is associated with the random, disordered motion of the molecules. An example of internal energy is compressed gases; since gases occupy the total volume...

Yes, heat can flow into a body without increasing the mean kinetic energy of its molecules. Transferring heat energy to an object will raise its internal energy, this will not necessarily cause an increase in temperture. Specific latent heat is the energy required to change the state of one...

Is the purpose of the 0th, 1st & 2nd Laws of Thermodynamics simply to legitimate the thermodynamic properties of Temperature, Internal Energy & Entropy, respectively? It seems that all these laws really do is establish that these properties are valid thermodynamic state properties and the...

I was going to put this in the homework forums, but on second thoughts it's more conceptual so perhaps here is better. It's about problem 4, chapter 6 of Wald. Part (a) is fine, $$u^a \nabla_a u^b = \frac{\xi^a}{(-\xi^c \xi_c)^{1/2}} \left( \frac{\nabla_a \xi^b}{(-\xi^c \xi_c)^{1/2}} +...

Hello. Questions: Are antimatter, dark matter, negative mass confirmed that they exist and exhibit as phenomena? What about dark energy and negative energy? Do these types of matter behave as wave also? Do they exhibit such behaviour? About those types of energy i said, can they be transformed...

First, in section 20.4, after listing all the things gravitational potential energy does not do, they say the equivalence principle forbids it being localized. I thought I understood the equivalence principle, but maybe I don’t. Any comments explaining that would be appreciated. Second, they...

If a system is in an eigenstate of the hamiltonian operator, the state of the system varies with time only with a "j exp(w t)" phase factor. So, the system is in a "stationary state": no variation with time of observable properties. But the system could in theory (for what I understand) be...

We know that energy can be converted from one for to another , but how does it do that? How exactly does energy interacts with the quantum particles or with strings for that matter?

How much energy is required to double the radius of a uniformly dense stellar object? Express the answer in terms of mass and the radius of the object.

I got 12/12 on the above part^ And as for the mathematical solution below I got 5/6 and then 2.5/3 for the conclusion.

I solved this problem easily using Newton's second law, but I had problems trying to use mechanical energy conservation to solve it. How I solved using Newton's second law: ##\text{(part of the rope that is on the left)}\, m_1=x\rho g,\, \text{(part of the rope that is on the right)}\...

Do you think Coke was thinking science when naming this "Energy drink" ?? Do they know how much energy zero calories represents?

Am i right Is internal energy for engineering just the sum of energy stored with a system of a substance. which is only affect by heat and work coming out of the system

If you search on-line for "efficiency of a black hole" you will get several discussions suggesting that the efficiencies of converting mass to energy are from 6% for non-rotating black holes to 42% for the fastest rotating black holes. I would like to know exactly how black holes convert some of...

Remind me please? In a three level system, with discrete energies E0,E1,E2: would light-shift (Stark shift), applied due to an external electric field, change the values of E1 and E2 by the same \Delta E? Or would \Delta E1 be different from \Delta E2?

I know the answer would be yes, but why? In class, I learned that energy is scalar and cannot be negative (at least in undergraduate class). Thus adding two sources of energy should result in a higher level of energy in general. But here for wave, if we have 2 waves that do destructive...

Hello there, I am interested in renewable or clean or new energy sources. What branch of physics that I need to focus on in order to get a deep understanding on this? Also, what prerequisites do I need? p.s. I am a self taught student, so I don't have any academic advisor

In Principles of Lasers by Svelto, while deriving the Planck radiation formula, equation 2.2.3 says $$I_{\nu} = \frac {c_0} {4n} \rho_\nu$$ where ##I_\nu## is the spectral intensity at some hole in the cavity wall (energy per time per area per frequency), ##c_0## is the speed of light in...

Hi, Could anyone please give me a little advice. If we look at a disc brake on a vehicle, the disc brake pads apply a friction force on the disk rotor which causes the kinetic energy of the moving vehicle to be turned into heat. Does this heat reduce the reactive force experienced on the disks...