Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [energy]

Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding [tag:energy-conservation] if it is specifically about its conservation.

6
votes
2answers
462 views

What is changing in latest light bulb technologies?

I'm confused with the latest home lightning bulbs. Understanding filament bulbs was easy. For example take 220V, 100W filament bulb: Power = $V^2/R$ Filament gets heated and emits energy in the form ...
2
votes
4answers
236 views

Energy quantization

Why does a free particle give rise to a continuous spectrum of energy eigenvalues while a particle in a bound potential gives rise to a discrete spectrum?
1
vote
2answers
81 views

What exactly is temperature?

I'm trying to have a really deep understanding of quantum physics and so I went back to what is blackbody radiation until suddenly I realized that my understanding of temperature is that of... well, ...
0
votes
0answers
10 views

An energy/model based controller to minimize overshoot and response time of a mass spring system

Consider a very simple system: $$m a + k x = F \, , \tag{1}$$ where $m$ is mass, $a = \ddot{x}$ is acceleration, $k$ is the spring's elasticity, $x$ is position of the mass and $F$ is the force from ...
-3
votes
0answers
38 views

Can a system that has no energy ,generate energy from nothing? [on hold]

Let's imagine a simple story : In the beginning there was NOTHING ,0 spacetime , 0 energy , 0 matter,no darkness,no light,no cold,no heat,0 dimensions, just absolute NOTHINGNESS.For energy to exist ...
7
votes
6answers
38k views

Is fire matter or energy?

I wanted to know that if FIRE is Matter or Energy. I know that both are inter-convertible. but that doesn't mean there is interconversion taking place just like nuclear fusion or fission. If it is ...
0
votes
1answer
137 views

Energy density and inernal density relations

If energy density relates to rest mass density as $\epsilon = \rho / c^2$. How internal energy relates to energy density? Also, when do we write $\epsilon = \rho / c^2$ an when $\epsilon = \rho / c ^2 ...
-1
votes
0answers
43 views

Can someone please help me to understand the following: force, work, energy, power, charge, voltage, amperage, wattage and kilowatt hour? [on hold]

I'm really bashing my head against the wall trying to understand the finer differences between some of these things. I thought I understood them until I reached my course on energy. I've lost so much ...
0
votes
1answer
19 views

Heat flow for an ideal gas in Isothermal Expansion

I'm having a bit of difficulty grasping the concept of heat flow in isothermal expansion -- most likely because I don't fully grasp the concepts yet. We were given a problem that the professor ...
4
votes
1answer
149 views

Mutual capacitance upper limit

I am having trouble making an analog for mutual capacitance from mutual inductance. In circuits with magnetic coupling, there is an upper limit established on mutual inductance due to energy ...
0
votes
1answer
150 views

About how much energy is transferred to a guitar when strumming it?

I'm curious as to how many calories(or joules) are directly transferred to a guitar through a player's arm and pick when strumming the guitar. Let's say that the player has an average weight (for the ...
0
votes
1answer
24 views

Bond graph, how to use it? [on hold]

Yesterday I heard the word "bond graph" and I felt like searching a bit about it. From what I understood, it is a graph that links the flow of energy between "states" in multiphysics systems. I am ...
3
votes
1answer
149 views

Are energy and momentum separable for EM waves

Everywhere I get to read statements like EM radiations and EM fields carry "energy as well as momentum " . I wonder if energy and momentum are inalienable . Is it possible for a field to carry only ...
0
votes
1answer
142 views

Using magnetic fields to fire plasma bolts

I very recently asked this question: Could you use magnetic fields to direct a bolt of lightning? As it doesn't seem feasible for what I have in mind, I decided I would instead ask if it's possible ...
0
votes
1answer
47 views

Energy formula for finite potential well [on hold]

The energy formula for infinite potential well is $$E=\frac{n^2h^2}{8ma^2},$$where $m$ is the mass of the particle, $a$ is the width of the well but in the case of finite potential well, I actually ...
-2
votes
1answer
24 views

Electrical energy generation by tangential wind? [on hold]

As shown in picture I want to get max energy output so what kind of analysis I should do for that?
1
vote
2answers
49 views

How can non-polarised light exist? [duplicate]

Typically unpolarised light is shown like this: Basically, from what I've seen, unpolarised light is just a lot of overlapping individual light waves. However, if they truly overlapped, would their ...
3
votes
2answers
3k views

Bound states, scattering states and infinite potentials

I am doing my first semester of Quantum Mechanics and we're using Griffith's Introduction to Quantum Mechanics. As he is introducing the Dirac delta function potential he explains bound and scattering ...
8
votes
7answers
87k views

How to deduce $E=(3/2)kT$?

It says in my course notes for undergraduate environmental physics that a particle has so-called "kinetic energy" $$E=\frac{3}{2}kT=\frac{1}{2}mv^{2}$$ Where does this formula come from? What is $k$?...
1
vote
3answers
73 views

Thermal energy turning into mass?

When you heat an object it's mass increases $E=mc^2$. What I don't understand is that this energy can be converted to mass and still be thermal energy too (object still hot). When a radioactive ...
0
votes
0answers
13 views

Why vertical wind turbine don't be half covered [on hold]

I think it would be more efficient for a vertical wind turbine to have a covered funnel about half of it Something like this figure It would protected the turbine from opposite wind and also ...
-4
votes
1answer
2k views

Joules versus newtons [on hold]

What is the difference between a Newton and a Joule? I know that a Newton is calculated by $F=AM$m but how is that different from a Joule, when a Joule is calculated by $K=1/2MV^2$ or $U= FX$? I am ...
1
vote
1answer
30 views

Free energy along a reaction coordinate

I've come into this issue when trying to understand biased sampling methods, in particular, umbrella sampling, but I think the question is more general. A recurring argument is that, along a reaction ...
1
vote
4answers
55 views

Bicycle Fuel equivalent on l/100km

Is there a way I can calculate the equivalent how much a Human powered bicycle consumes in the equivalent l/100 Km of Diesel fuel? And also can I calculate the same for Gasoline fuel? And for ...
0
votes
0answers
17 views

Energy of a Harmonic Progressive Wave

In a harmonic Progressive wave all the particles of the medium perform Simple Harmonic Motion. In case of SHM, when the kinetic energy is maximum the potential energy is minimum and vice versa. Is the ...
6
votes
3answers
695 views

Where does the energy of noise cancellation go?

This is related to this question on Aviation.SE about noise cancelling headsets. We know that soundwaves can be superimposed on each other. Therefore, by taking an existing sound wave and producing a ...
0
votes
3answers
59 views

Could pressure differentials be used to produce power?

There is potential energy between something like a vacuum in a container and a gas on the outside of it, or vice-versa. Could this energy be harvested in a vacuum, or close to vacuum situation like on ...
0
votes
1answer
42 views

Centripetal force related problem [on hold]

If a bike rider constantly keeps rotating on a vertical circular path, what is the required minimum velocity on the highest point of the circle to keep him on the circular path without falling?
0
votes
0answers
52 views

Mometum vs kinetic energy (vis viva), How nature by experiments show these on same objects? [closed]

Momentum was proposed by Isaac newton and kinetic energy(vis viva) was proposed by Gottfried Leibniz . how these two quantities different and understand intuitively and experimentally. For example if ...
0
votes
1answer
45 views

Eigenvalues of the Hamiltonian

Is every eigenvalue of the Hamiltonian a form of energy? If not are there values of the Hamiltonian that do not correspond to the energy of the system?
0
votes
1answer
152 views

Mass due to the ionization energy of the hydrogen atom from $E = mc^2$

Using $ E = mc^2$ I want to calculate a hypothetical mass from the first ionization energy of the hydrogen atom. The ionization energy is given in units of $\rm kJ/mol$ which could seemingly be ...
1
vote
2answers
147 views

Work done relation to potential energy

I know work done is negative of change in potential energy, I.e., $W=-(∆U)$. It means that Work done against a force (or work done on a system) increases its potential energy. And Work done by a ...
2
votes
3answers
1k views

In continuum mechanics, what is work potential in the context of total potential energy?

I'm reading a book on the finite element method. Specifically I'm looking at the background material where they are discussing potential energy, equilibrium, and the Rayleigh–Ritz method. The book ...
0
votes
2answers
43 views

Falling from a high cliff [closed]

I've always wondered about the reason why falling from a high cliff could actually cause death, is it the normal force exerted back from the ground? or is it related to energy? or what? thnx.
-1
votes
2answers
49 views

Constant gravitational acceleration $g$ and energy

I've been taught that $g$ is constant for different masses and that if I were to drop a heavy object and a light object from the same height then they would reach the ground at the same instant with ...
1
vote
2answers
58 views

Interpretation of the energy-time uncertainty [duplicate]

From the uncertainty relation it follows that: $$\Delta E \ \Delta t = \hbar$$ $\Delta E$ is the energy uncertainty of a state, $\Delta t$ should be the uncertainty of the lifetime $\tau_b$ of the ...
5
votes
1answer
3k views

Thermal de Broglie wavelength - definition

The thermal de Broglie wavelenght is often defined by the formula $$\lambda=\frac{h}{\sqrt{2\pi mkT}}$$ but equally frequently is it defined as de Broglie wavelength for a free ideal gas of massive ...
1
vote
1answer
175 views

Do circularly polarized photons have more energy than linearly polarized photons?

If the energy of a single photon is given by $E=hf$ then a linearly polarized photon has an energy E which is dependent on only its frequency. But a circularly polarized photon also has this same ...
-1
votes
2answers
140 views

Should I walk or run to my towel when naked and wet? [closed]

This morning when I got out of the shower, I realised I had left my towel in the bedroom. Naked and wet I ran as fast as I could to get the towel. On my way back I didn't run, but rather walked, and ...
3
votes
2answers
213 views

Is energy $E$ in Schrödinger equation an observable/ Can $E$ be measured?

There is something I am missing. Take this quantum approach to estimate mean energy of a molecule: $$\langle\psi|H|\psi\rangle=\overline E$$ Question: Is $E$ an observable? If it is, how to ...
1
vote
1answer
67 views

energy storage and flux produced by an inductor

The unit of magnetic flux is the Weber and is proportional to L x I or Henrys X Amps. Flux is also proportional to J/I or energy per Amp. Energy stored in an inductor is given as 1/2 LxIxI. When I ...
0
votes
1answer
39 views

“Plushness” of a simple mechanical damper?

What heuristics generally define the "plushness" of a mechanical damping or braking system? For example, if a person or some mass is to collide with a fixed wall or the ground (e.g., after a vertical ...
0
votes
0answers
33 views

Calculate the acceleration of a drone [closed]

It is for my final year project as a Computer Science student. I am building a desktop app drone simulator and I need some help with the Physics part of it. The scenario is as follows: I have a drone,...
1
vote
1answer
31 views

How does kinetic energy change into different forms of energy?

Is the kinetic energy the only thing that is generating heat when you rub your hands together? If so, exactly how does it do this? How does kinetic energy change forms? If not, what other energy forms ...
3
votes
3answers
132 views

Classical Mechanics: work

This a a fragment from my Theoretical Physics (- Classical Mechanics) notes: $$W_{1 \to 2} = \int_{t_1}^{t_2} \boldsymbol{F}\cdot\boldsymbol{v}\,dt = m \int_{t_1}^{t_2} \dot{\bf{v}}\cdot{\bf{v}}\,...
0
votes
3answers
5k views

Is magnetic wheel possible?

I once tried to make a magnetic wheel using different shaped magnets and placing them in different orientations and of different shapes.But it did rotate making a small angle ie it didnt rotate even a ...
-1
votes
4answers
60 views

How much energy is in a 75 kg human being? Including atomic and electrical (charge) [closed]

To calculate the energy in 75 kg of mass is easy with E = mc2. But, how to calculate how much charge are in all our atoms? It is, too, a gargantuan amount of energy.
0
votes
3answers
472 views

Question on work, energy and power

The engine of a train is working at a constant rate. The maximum speed of the train up a certain incline is $V_{1}$ and the maximum speed down the same incline is $V_{2}$. Then if the train moves on a ...
0
votes
4answers
64 views

What is heat and heat transfer?

Physics books write that heat is the transfer of thermal energy. They also write that heat transfer is the transfer of thermal energy from a thermodynamic system of high temperature to a one of lower ...
1
vote
0answers
8 views

How to calculate energy (KWh) from Temperature (T),Air quality (Co2), and illumination (lux)?

I have data of temperature, air quality, and illumination.I want to calculate energy consumption (KWh) from these parameters.My data is shown in the image . Also, examples are also shown in image 2 .