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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0.19 kg apple falling (a problem on Work and Power)

Problem A 0.19-kg apple falls from a branch 3.5 m above the ground. a) Does the power delivered to the apple by gravity increase, decrease, or stay the same during the time the apple falls to the ...
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19 views

Specific Heat capacity [on hold]

The total heat capacity of a caloriemeter, heater, stirrer is 107 joules per kelvin. Mass of the liquid in caloriemeter is 0.241 kg. The power supplied by heater is 41.48 watts. The initial rate of ...
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1answer
20 views

How is there GPE in objects that are on top of a hill?

What I don't understand about gravitational potential energy is that objects have the greatest GPE on top of a hill and it decreases as they go down the hill. At the top of the hill, they are on the ...
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1answer
34 views

How does parallel plate lose energy when deflecting charged particles

Say you have a parallel plate setup, each plate is charged with ±Q of charge, and is then disconnected from the power source and is insulated from the environment. There is no way the plates can be ...
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1answer
34 views

Energy of electromagnetic wave

Its given here that energy density of an electromagnetic wave is $$\vec S=\frac{1}{\mu}(\vec E\times\vec B)$$ How is the above expression derived? And when did energy become a vector? I though work ...
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1answer
24 views

Where are the electron exchanges happening in solar cell physics when considering the photon?

When considering solar panel physics, are we taking an electron from Light(photon), or is the energy of Light causing an electron to jump in said solar cells through excitation? Is the photon even ...
3
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1answer
37 views

Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
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0answers
25 views

How would you calculate consecutive bounces on a trampoline to find how much energy is lost each time or what percentage is lost each time? [on hold]

How would you calculate consecutive bounces on a trampoline to find how much energy is lost each time or what percentage is lost each time?
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1answer
37 views

Can the internal energy of an ideal gas system increase as temperature decreases?

If $\Delta U = Q + W $ Then adding $x$ moles of an ideal gas of lower temperature into a system of internal energy $U$ would increase $U$ as the kinetic energies of the molecules of the colder gas ...
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0answers
28 views

Calculating the data rate for a baud signal [on hold]

I have been working on these questions for the past few hours. I am working on calculating the data rate of baud signals, where each symbol can take on one of two levels. I wanted to know if I have ...
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3answers
61 views

is the potential energy of a black hole infinity

It appears like black holes posses an escape velocity greater than the velocity of light. It takes an atom infinity energy to travel at speed of light.Do black holes posses that energy to retain ...
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1answer
47 views

What would happen if you were to release the energies of the big bang in our universe a second time? [on hold]

Would it just wipe out everything, or would something else occur?
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0answers
41 views

Can the linear momentum of a system be constant, even though its centre accelerates?

My instructor says if the velocity of center or mass is constant, it means that the linear momentum of a body is conserved. So if no external force acts on a body, there is no change in the linear ...
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1answer
25 views

“Carbon capture into fuel” - where does the energy come from?

I recently found an article titled "Scientists find a way to convert Carbon Dioxide from air into fuel" (here), and my immediate reaction was "surely not - the energy balance would kill you right ...
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1answer
33 views

Why am I not shocked when I touch a tree, and the tree touches a power line? [on hold]

Why am I not shocked when I touch a tree, and the tree touches a power line?
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1answer
16 views

How could the BOE (barrel of oil equivalent) be measured?

The barrel of oil equivalent was given as an example of gigajoule scale energy. "The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel ...
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0answers
50 views

If a system has an internal energy equal to 0, does this mean it doesn't exist?

Enthalpy is a measure of energy in a thermodynamic system: It includes the internal energy, which is the energy required to create > a system, and the amount of energy required to make room for it ...
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1answer
48 views

What makes cart with a moving object in it gain speed (no friction anywhere)?

I would like to understand what makes the cart below the moving object move. There is no friction between any of the objects. The cart is moving therefore there is force applied to it. The only force ...
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1answer
36 views

If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
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1answer
21 views

Microwaving two products based on individual instructions

Suppose I have a cake, which has instructions to heat it for 60 seconds in the microwave. I also have some custard, which has instructions to heat it for 30 seconds in the microwave. For convenience, ...
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1answer
24 views

Actual electricity usage to maintain a constant water temperature

How can I easily measure (or determine) the actual electrical usage necessary to keep a constant temperature for my water heater?
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0answers
17 views

Which ball travels further, one that is thrown up a frictionless ramp or one that is thrown in the air? [on hold]

They are thrown at the same angle, and their masses are equal. Please explain using basic physics, if you can. We only learned: Kinetic, potential energy Work Velocity
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1answer
98 views

How likely is negative energy to exist?

Negative Energy is the exact opposite of ordinary energy as it would move in the opposite direction from its momentum and accelerate in the opposite direction of an applied force. It would also warp ...
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1answer
64 views

Does this count as a proper derivation of the formula for work and kinetic energy? [closed]

$v_{av}$ = average velocity, $d$= distance, $a$ = acceleration, $m$ = mass Given: $$v_{av}*t=d$$ $$t=\frac{v_f-v_i}{a}$$ $$v_{av}=\frac{v_f+v_i}{2}$$ Then: $$\frac{v_f+v_i}{2}*\frac{v_f-v_i}{a}=d$$ ...
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1answer
77 views

Photons Disappear and Reappear from Atoms?

Where does photons come from and disappear to? Can photons be destroyed and created? Without atoms would photons exist?
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1answer
54 views

Why do we hear the square of the wave?

Assume we superpose two waves of frequencies $\omega_1, \omega_2$. Then what we get are beats. Adding the two sines gives us $$\psi = A\sin(\omega_1 t) + A\sin(\omega_2 t) = 2 \sin ...
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Calculating potential energy per ion of an one dimensional ionic crystal

The problem states to calculate "the potential energy, per ion, for an infinite 1D ionic crystal with separation $a$"; the crystal is a 1D lattice of alternating charges, likes so: ...
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How to efficiently cool down simulated gas by time-dependent potential?

I'm trying to simulate condensation of a highly diluted gas (a model gas, not any real one). For simplicity I restrict the simulation to 2 dimensions. To setup the simulation I take some interparticle ...
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1answer
37 views

Will the energy of gravitational collision be the same?

If you put two small stationary spherical objects (say 1 meter wide weighting 1kg) 1 light year across and let them collide after some time. Will the energy of collision be the same as if you put ...
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0answers
23 views

Efficiency of resonant inductive coupling as a function of distance

What is the relationship between the efficiency of energy transfer between resonant inductive coupling between two coils, and the distance between the coils?
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2answers
43 views

Question about Kinetic Energy and Force acting on a body

Below is the graph of a body that rests on a friction-less flat surface. On this body force F is applied and it's value is being depicted in the graph below. We can see that the body moves from point ...
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2answers
32 views

Is there a base or fundamental state of energy? [closed]

Is there a base state of energy? By base state, I mean if a certain amount is in no other state like heat, light, magnetism it just stays in the base state. If not, why not? Also, is there a list of ...
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0answers
20 views

Will Energy and Work equal to each other between two closed systems linked by one shareable object?

Two closed systems are linked to each other. Both use same object. In one of this closed systems was spent energy to change physical property of shareable object. After this object transformation, ...
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1answer
35 views

Internal energy + energy of electron

Internal energy of a system composed of molecules or atoms is the mean energy of all these particles in the system (energy as kinetic energy, potential energy etc..). But what I am seeing that we are ...
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3answers
50 views

Is $\Delta H$ equal to $\Delta Q$?

I will use $\Delta$ to denote "change in something". $\Delta U = \Delta Q+\Delta W$, where the signs have been assumed to be positive (work is done on the system and heat is absorbed). But also ...
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1answer
61 views

Is $E = p^0$ in non-inertial frames?

In special relativity the energy of a particle is the 0-component of the 4-momentum. However, is this still true in non-inertial frames, and in particular in non-freely-falling frames in general ...
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2answers
74 views

Frames of reference, energy and different observations (non-relativistic)

I have had trouble reconciling the quadratic form of kinetic energy and reference frames traveling at different velocities for some times now. I'll give an example that confuses me for some ...
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0answers
20 views

Does an electron's energy decrease while performing its motion? [duplicate]

While revolving around the nucleus if the electron's energy decreases then will it hit the nucleus and if it does what will happen?
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0answers
24 views

What impact has air resistance beneath vehicles? [closed]

Let's say that a car travels 100km in one hour consuming 5 litters of gasoline. How much gasoline would consume this car if between the left and right wheels would be a deep hole, meaning that there ...
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3answers
114 views

Can the kinetic energy be a function of the position vector?

,I got one confusion when reading Goldstein's Classical Mechanics (page 20, third edition). After getting the equation $$ \sum \left\{\left[\frac{\mathrm{d}}{\mathrm{d}t}{\left(\frac{\partial ...
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31 views

Energy concept and calculuation

Could someone please explain how the concept of energy was conceived and how it evolved into our modern understanding of it ? Also, how did people come about various ways of mathematically ...
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3answers
91 views

Could sound be considered a kind of renewable energy? [closed]

Is sound energy useful as a source for generating electricity? If so, could it be a renewable resource?
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1answer
50 views

Why won't this Casimir effect perpetual motion machine work?

So the Casimir effect is caused by an imbalance in radiation pressure(caused by virtual particles) on two sides of a metal plate. This is typically shown with two close plates getting pushed towards ...
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1answer
51 views

Energy of hydrogen atom - Schrodinger equation [closed]

The wavefunction of the electron in the hydrogen atom is $ k* exp(-r/a)$ (k is the normalization constant), but it does not take n into account, whereas the solution of Schrödinger's equation ...
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0answers
36 views

Self-powered heat exchanger w/energy profit? [closed]

It is possible, considering the laws of physics, to build a heat exchanger that runs on the power it gathers from the environment? A typical heat exchanger uses less power to harvest heat for a ...
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2answers
83 views

Heat diffusion in a house

I was wondering about this problem (which is NOT homework, it's one of my mental problems due to what surrounds me): supposing I'm in a room, and it's winter. Heating is on, the boiler works and the ...
2
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2answers
68 views

energy of a ball [closed]

What is the energy of a ball lying on the ground at rest? As it is not in motion, it will have zero kinetic energy and as it is lying on the ground its potential energy will also be zero, taking the ...
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2answers
39 views

What's the minimum kinetic energy required to overcome static friction?

Suppose I have a still (granite) cube on a flat surface with friction with gravity evenly pulling down on everything. I know how to calculate how much force something such as electromagnetism would ...
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1answer
52 views

Given a current velocity and a fixed input energy, how much faster will a relativistic particle be?

The relativistic kinetic energy of a particle with mass $m$ and velocity $v_0$ is $$m c^2 (\gamma_0 - 1) \textrm{ where } \gamma_0 = \frac{1}{\sqrt{1 - \frac{v_0^2}{c^2}}}$$ I would like to know how ...
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Do we know how much energy is released in internal conversion (fluorescence)?

In the Jablonski Diagram, when photons hit a surface and certain frequencies are absorbed, then internal conversion occurs to the excited portions of the surface and energy is released as heat (If I ...