Energy is a quantity which gives an overview of the amount of work doable by the system.

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How to derive energy expressions thinking of it as a conserved quantity only?

By now I understand that "energy is a conserved quantity" and that's all we need to know. Then, the idea of work comes as the change in kinectic energy of a system and we realise that having energy is ...
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1answer
36 views

Work done (by gravity) on paired blocks [closed]

Why does gravity do more work on the block going down? The total work done (by gravity) on the $8kg$ block is more than the work done (by gravity) on the lighter block. How?
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How will a particle with energy less than $V_{\rm min}$ behave?

Consider e.g. the finite square well: $V = -V_o$ between $x=-a$ and $x=a$, $V=0$ elsewhere Now for scattering states, $E$ must be $> 0$. For normalizable bound states, $E$ must be $< 0$ and ...
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66 views

How does negative energy from Hawking Radiation cause a Black Hole to shrink? [duplicate]

Hello this is expanding upon a question that was previously asked on stack exchange that I linked below. From what I understand of Black Holes is that overtime Hawking Radiation results in the Black ...
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1answer
602 views

What is negative Energy/Exotic Energy?

So I have been researching around a little as I am highly interested in Astrophysics and I came across an energy I have never heard of before; negative energy also commonly known as exotic energy. Now ...
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373 views

kinetic energy in collisions [closed]

We were hoping you could help us understand collision energy. Vehicle $ A $ is driving West at $35\space mph$ and weighs $ 1437 \space kg$. Vehicle $ B $ is driving North at $35\space mph$ and weighs ...
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259 views

Travel at the speed of light

Is it me who have a poor understanding, or does all matter have to become 'pure energy' in order to achieve speed-of-light speed? If so, does that mean that no material can achieve the speed of ...
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Mean energy harmonic oscillator

I know that for a particle under the potential $$V(x,y,z)=\frac{k}{2}(x^2+y^2+z^2)$$ the equipartition theorem says that it contributes to the mean energy to $\frac{3k_BT}{2} $ (one half for each ...
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1answer
67 views

How much computer power would we need to model every physical aspect of the universe [closed]

So I know there are equations that give you the total energy in the Universe(Friedman). So about if we we to simulate every single interaction from neurons to physical forces, strong and weak, ...
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331 views

Energy needed for Superman to take off and fly at the speed of sound

I just watched "Man of Steel", and I'm wondering if my logic is correct. Let's assume Superman is 80 kg. The energy required to take off from the rest to reach the speed of sound in air (if I neglect ...
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2answers
41 views

Query into the cumulative velocity of mounted platforms

Consider throwing a stone at an object from rest, it travels at Vms-1. Now throw that stone whilst running at Ums-1. It seems in the latter scenario the total speed of stone is V + U. Now imagine ...
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4answers
48 views

Relation between Force, Time, and Energy

Is energy involved independent of force applied over time? In other words, if I wish to apply a force for much more time would I require more energy?
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39 views

The context of definition of work [duplicate]

It is unclear whether the work is defined considering opposite force on the same body or in ideal case where there is a single force acting on a body.If we consider ideal case where only a single ...
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1answer
73 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 ...
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3answers
34 views

Energy, time and force

Consider force $F$ acting on a body of mass 1000kg and the displacement be $s$. So energy required to do so is $F$x $s$. Now consider the same force causing same displacement on body of mass 1kg. ...
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1answer
35 views

How does electric current generate thermal energy?

How does free electrons moving through a wire cause random vibrational motion of the positive ions?
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1answer
32 views

Can a laser be designed to ionize muons so as to prevent a-sticking?

Muon catalyzed fusion is currently little more than a lab curiosity today in part because of how many hydrogen nuclei can be fused before the muon is carried away by an alpha particle. ...
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1answer
47 views

What is Work? What does the quantity suggest intuitively? [duplicate]

The mathematical formula for work says that work is force into displacement, but what is the philosophy behind it? I mean what does the quantity suggest?
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1answer
39 views

How did Lyman discover his series?

How did Lyman discover his series in hydrogen atom? How did he know that the final energy level is the first level and not the second or the third or etc.? Or how did the other scientists know which ...
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2answers
70 views

Potential energy of an infinitesimal length of elastic rod

I am having an embarrassingly hard time with the derivation for the potential energy of an infinitesimal element of an elastic rod of area A. The picture shown below is an element of the rod that has ...
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4answers
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Can one obtain free energy from the vacuum?

It is known that from the vacuum of a quantum field theory, virtual particle pairs are created and destroyed; is it possible to capture these particles thus obtaining free energy from the vacuum?
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4answers
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Optimizing water boiling

I'm about to prepare some spaghettis and to do so I need 2 liter of boiling water. For getting the water to certain temperature (lets say 100 Celsius degrees) from a starting temperature of 15 ...
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9answers
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Why is torque not measured in Joules?

Recently, I was doing my homework and I found out that Torque can be calculated using $\tau = rF$. This means the units of torque are Newton meters. Energy is also measured in Newton meters which are ...
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3answers
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What happens to gravity after matter-antimatter annihilation?

Both matter and antimatter have mass and thus gravity, but since energy from annihilation has no mass what happens to the force of gravity that was previously present? What about conservation of ...
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Am I understanding power correctly? [duplicate]

4 men weighing 380kg, carrying a 380kg piano up 5 meters will generate 31 watt if the load takes 20 minutes. Now this is very hard to do and saps the strength out of any human being. However, that ...
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2answers
74 views

Do there exist objects that absorb energy only (and do not give it away)?

Do there exist objects that absorb energy only (and do not give it away)? Magnets have been mentioned in this post, do we know more examples? Extract energy from magnets And how is this capability of ...
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1answer
22 views

Excited Energy levels of Hydrogen vs Solids

My question has to do with Excited Energy Levels. I keep reading and learning that all objects/most solids emit infrared radiation. But to emit radiation, an object's particles must first enter a ...
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7answers
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Can energy be taken out of the QFT vacuum?

There have been recent questions about the vacuum. In my simplified knowledge the vacuum is like a ground state energy level, and also that there might even exist other lower energy levels than the ...
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Could the Planck energy destabilize quantum vacuum?

Could an advanced type III civilization, being able to harness the Planck energy (10^19 GeV), destabilize the quantum vacuum, creating a new phase of true vacuum?
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How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
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1answer
106 views

What do we mean when we talk about Gibbs Free Energy?

Before I start, I'm aware that this question may be better suited on the Chemistry or Biology site, but it's my belief that physicists are more likely to have a clear understanding on what certain ...
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2answers
177 views

Does magnetic geometry determine the scaling of a Polywell fusor?

Does magnetic geometry determine the scaling of a Polywell fusor? Forgive imprecise terminology here - by "magnetic geometry" I mean the configuration of the magnets, the configuration that creates ...
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1answer
83 views

The relation between the movement of electrons and energy

So, I've been enjoying reading a lot of helpful posts, but now, I found myself in the need of asking something. I have a hard time grasping the general concept of electricity / how the relation ...
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1answer
40 views

Could there be massive gravitons and in our spacetime? [closed]

My question is: Could there in principle be sub-groups of gravitons (if they existed) that has mass (and in our spacetime dimensions) such as those affected by electric or by strong force or other ...
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1answer
54 views

Rigid body problem

I have some doubts about the next excercise: A bar of length $2a$ and mass $m$ moves freely with both of its extremes on a ring of radius $\sqrt2a$. The ring can rotate freely in a certain ...
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What is Fermi energy and Fermi level? [duplicate]

What is meant by Fermi level and Fermi energy? And what is the difference between the two?
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1answer
24 views

Energy Stored in a Capacitor with and without Dielectric

I have seen the equation $V = \frac {V_0}{K}$, but also the equation $V=\frac{1}{2}CV^2$. The values of C and V increase in the same linear ration with K (because $C=KC_0$). However, as the energy ...
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1answer
56 views

How does someone move space?

I've heard that we've known components of the universe appear to be flying apart faster than $c$, and that this can happen because the space containing these materials are also moving apart. How does ...
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1answer
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What are the restrictions on the Hamiltonian in QM?

In quantum mechanics, we usually write the Hamiltonian as: $$\hat{H}=\hat{T}+\hat{V}$$ But in classical mechanics, there are several reasons why it would not have this form: We've chosen some ...
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Reducing the Tsunami impact using Nuclear bombs [duplicate]

I am a novice on this topic. However, I wonder if we use nuclear bombs against the tsunami, will it reduce the speed and impact of the tsunami. Is it possible to break the massive wall of waves using ...
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3answers
754 views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
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1answer
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Does quantum collapse involve a loss of information? Does it require energy as suggested by the Landauer Limit?

I read in the context of quantum computing or of the minimal energy required for computation that there has to be a minimum possible amount of energy required to change one bit of information, called ...
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4answers
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Why can't energy be created or destroyed?

My physics instructor told the class, when lecturing about energy, that it can't be created or destroyed. Why is that? Is there a theory or scientific evidence that proves his statement true or ...
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3answers
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How can I determine density of a gas only given temperature?

I have a homework problem where exhaust is traveling through an exhaust system (assumed to be air for simplicity) from and engine and then released into the atmosphere. The exhaust is at a temperature ...
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1answer
66 views

Kinetic energy question

Thought experiment: I am starting to walk on a coridor... From the coridor's perspective I have a certain increase of kinetic energy. From my perspective the whole universe is gaining kinetic energy ...
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1answer
74 views

How is the energy of a lightning calculated?

I was wondering how is the energy of a lightning measured? Is it based on the luminous intensity and/or the generated sound? What about the generated heat and energy spent in the production of ozone? ...
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What's this about kinetic energy increasing with the fifth power of length?

I don't quite understand this quote from Stephen J. Gould's Ever since Darwin, where he talks about the compensating physical characteristics of organisms for their size. Other essential features ...
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2answers
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Total energy of a quantum gas

I'm dealing with a quantum gas, thought as a system of N non-interacting particles. I would be tempted to say that the total energy of the system equals the sum of the energies of the single ...
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7answers
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How can kinetic energy be proportional to the square of velocity, when velocity is relative?

Let's start with kinetic energy (from los Wikipedias) The kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a ...
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Where does gravity get its energy from?

I would like to know where gravity gets its energy to attract physical bodies? I know that the law of conservation states that total energy of an isolated system cannot change. So gravity has to be ...