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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.

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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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?
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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?
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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 ...
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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.
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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 ...
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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 ...
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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,...
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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 ...
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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 ...
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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 ...
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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.
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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 ...
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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}}\,...
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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 .
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1answer
20 views

Damped oscilliations on a ball rolling in a U-shape

How do you calculate the rate of loss of energy on a ball moving in a U-shape (half sphere)? Can I simply look at the height of the ball at its peaks and measure the difference between the potential ...
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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 ...
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1answer
22 views

$p$-$V$ diagram and internal energy

I recently learned that if the initial state is equal to the final state in the $p$-$V$ diagram then the internal energy is equal to zero so that means $Q=W$. My question is how can you know that only ...
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0answers
30 views

Why is energy proportional to light's frequency? [duplicate]

I can appreciate that light can be quantised into photons, but I'm having a bit of difficulty understanding Planck's formula $$E=hf$$ Perhaps I am lacking intuition, but I don't really see why higher ...
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3answers
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Why is a particle non-relativistic when its kinetic energy is small compared to its rest energy?

For example, nucleons in nucleus are in motion with kinetic energies of 10 MeV. Their rest energies are about 1000 MeV. Kinetic energy of nucleons is small compared to rest energy. They are hence ...
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3answers
147 views

Superposition principle forbids quantisation?

Apparently bound states in quantum mechanics require energy states to be discrete. That means energy in such systems is quantized, right? However, say that we have a superposition of energy ...
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1answer
84 views

What is energy in quantum mechanics?

Is it wrong to say energy is the expectation value of Hamiltonian? Or should I say energy is the eigenvalue of Hamiltonian?
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1answer
16 views

Energy conversions due to movement of car up the slope

We know if a car is travelling at constant speed up the hill then the power output of engine is equal to change in gravitational potential energy per unit time . (Assuming friction negligible). What ...
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0answers
14 views

information conservation

Since according to the unitarity principle the total amount of information in the universe is conserved over time, how was this information generated ? Is there a relationship between energy ...
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0answers
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Quantisation of radiation energy [duplicate]

I am currently studying about the dual nature of radiation and matter. I have come across how the radiation energy is quantified by saying that it is built up of discrete units. Though I fairly have a ...
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1answer
55 views

From the perspective of QM, how can a thermodynamically isolated system can have a constant internal energy $U$?

In thermodynamics, we assume that an isolated system has an internal energy $U$, and if there is no heat given, or work done by/to the the system, this energy is constant. However, in QM, we do know ...
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1answer
42 views

If kinetic energy is mass times the integral of velocity, isn't it just a product of mass times distance? [closed]

I'm still learning Calculus at the moment and I'm currently on integration. The moment I realized the "$1/2$" and square value in $v^2$ are just products of integration, can't one just use ...
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0answers
14 views

Work done by friction on a oscillating disc without slipping in a circular path

Say a disc is oscillating without slipping in a circle about its stable equilibrium. I've thought of it this way: I assumed a disc is placed at, say, 3 degrees from the equilibrium. The rotation ...
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1answer
57 views

Energy and mass at absolute zero temperature

Hi my question is if the temperature of a particle is reduced to absolute zero the that particle has lost its energy so it has no movement. Particles have mass and Einstein said mass equates to energy....
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0answers
10 views

Speed of spherical projectile after x meters, considering air drag

I'm trying to write a bb gun calculator on my site, but unfortunately I'm not good at physics. This is the scenario: If we have a projectile with a mass of 0.5 grams, leaving the barrel at 400 ...
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2answers
74 views

Why is electric power needed at all when elevator is descending?

If the ropes are doing negative work on lift, why is electric energy needed? And why is there a limit on number of passengers in a lift in this case?? Please explain in terms of energy conservation ...
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2answers
42 views

Gravitational potential energy of a rod, attached by its end to an axis

Situation: We suppose a rod is attached by its end to some pivot, and is allowed to fall from a horizontal position. As this occurs, the rod loses gravitational potential energy ($∆U_G$), say 10J, ...
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1answer
44 views

Internal energy is defined up to constant

Let have $n$ mole of substance which is taken as an ideal gas. The internal energy is \begin{equation} U(n,T) = n u(T), \end{equation} where $u(T)$ is the molar internal energy which obeys \begin{...
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1answer
38 views

Can electrical energy be changed into potential energy?

If I boil some water on an electric stove, will the heat energy imparted change into potential energy (state changes: water to steam).
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5answers
106 views

If mass can be converted to energy than how is it said that energy can't be created?

From the mass-energy equivalence E=m(c*c), it can be seen that energy can be created and it is not converted from one form of energy. Or am I wrong ? Can you explain?
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1answer
53 views

Rotational work done

So the formula for rotation work is $$\mathrm dW=T\cdot\mathrm d\theta$$ where T is torque. While solving a question like in case of a body rolling down an incline (pure rolling), we usully equate ...
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0answers
29 views

Muons that decay in plastic scintillator

I have a question on the energy of the muons that decay in a plastic scintillator. In these notes, at page 4, fourth line from the end, it is mentioned that muons with less than about 50 MeV will ...