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

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1answer
38 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
69 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
2k views

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
41 views

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 ...
19
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9answers
6k views

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 ...
7
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3answers
557 views

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 ...
0
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0answers
17 views

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 ...
0
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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
21 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
1k views

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 ...
0
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0answers
37 views

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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0answers
54 views

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 ...
7
votes
1answer
98 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 ...
3
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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 ...
1
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1answer
77 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 ...
0
votes
1answer
39 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 ...
0
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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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0answers
19 views

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?
0
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1answer
20 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 ...
0
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1answer
55 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 ...
6
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1answer
101 views

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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3answers
1k views

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 ...
0
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3answers
733 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 ...
8
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1answer
112 views

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
7k views

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
2k views

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 ...
4
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1answer
65 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 ...
2
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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? ...
0
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1answer
45 views

What happens to gas molecules after Ionization?

I know that gas molecules conduct electricity after they get ionized but what will happen if we keep increasing the voltage even after ionization? Will it explode? If it will then how much energy ...
8
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2answers
465 views

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 ...
0
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2answers
40 views

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
3k views

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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6answers
3k views

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 ...
1
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1answer
105 views

How to calculate the amout of time for oil to get out from a pneumatic cylinder?

I have a system. You can assume it is just a 1" diameter steel pneumatic cylinder (1 foot long). Assume we ignore the bore size issue at this point. One chamber is filled up by oil (6" of volume), ...
5
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2answers
143 views

How do collisions of fundamental particles produce different fundamental particles?

When considering fundamental particles as waves in fields, it seems like any collision of two particles of some fundamental type could only create energy within that type's field. Why do we expect ...
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0answers
36 views

anti-matter activation energy

In chemical reactions, there are usually energy barriers that must be overcome before a reaction can take place. It seems that such a phenomena also exists at the atomic level as well. For instance, ...
6
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4answers
17k views

What is the relationship between kinetic energy and momentum?

I can't seem to figure out the relationship between $E_k$ and $p$ or $F$. I understand that the units are pretty different. But for example: A bullet with a mass of 10.0g is moving at the speed of ...
2
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2answers
110 views

Does “Crack The Whip” actually speed you up?

"Crack The Whip" is a game played on ice skating rinks where several individuals line up all facing the opposite end of the rink, and skate forward. When the group reaches the opposite end of the ...
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1answer
35 views

Resource(s) for developing a good understanding of surface tension?

I have read through several junior undergraduate level explanations of surface tension. Here is a typical presentation at that level: Molecules at the surface of a fluid experience approximately ...
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3answers
45 views

Creating electricity from mains water pressure.

Could someone cleverer than me help me out? I had a crazy thought going through my head the other day and I can't lay my mind to rest until I get an answer. Q. How much energy could be produced by ...
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2answers
56 views

Conservation of Mass, Momentum and Energy - Airburst Rounds

I have a airburst round with set amount of fragments with a certain shape inside my bullet. After a certain distance has travelled, a charge explodes in the back of the round disintegrating the shell ...
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2answers
79 views

How rigorous can conservation of energy be made?

The principle conservation of energy is often taken as an obvious fact, or law of nature. But it seems to me the definition of energy is far from obvious, or natural: ...
7
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3answers
838 views

Explain how (or if) a box full of photons would weigh more due to massless photons

I understand that mass-energy equivalence is often misinterpreted as saying that mass can be converted into energy and vice versa. The reality is that energy is always manifested as mass in some ...
2
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2answers
118 views

If energy is just a conserved quantity how can it have flux and density?

As I'm very well convinced for now, the better understanding of energy we have today in Physics is that of a conserved quantity, i.e, a numerical valued associated with a system that remains the same ...
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2answers
130 views

Why do we calculate energy by integrate the Signal squared?

What's the interesting thing in the square of a signal? I know integrating gave us the sum of the differentiated energies, but why the Energy is the square of the signal?
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3answers
356 views

How does water falling down a waterfall gain energy?

I'm kind of a noob in the physics area. But I know that energy cannot be created, it can only be transferred. So how and what "type" of energy does water get when free-falling?
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1answer
40 views

Work-Energy-Power Relations

A wind-powered generator converts wind energy into electrical energy. Assume that the generator converts a fixed fraction of the wind energy intercepted by its blades into electrical energy. ...
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0answers
32 views

Can Somebody give me Questions [closed]

Can someone give me questions on physics because I have my Examination tomorrow Class 9th (CBSE) topic : - Fluids(Density,buoyant Force , Archemedis Principal) , Work Power Energy(Work Basics, ...
0
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2answers
106 views

what is “work”? (of a force)

I would like to know why two forces (of different magnitudes but same direction) that we'd use sequentially on an object to move it by the same amount twice, will produce two different values for the ...
2
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0answers
52 views

What's the connection between being homogeneous in energy and having a proper time scale?

Towards the end of page 8 of this scientific paper, I have found the following sentence: ...given the fact that the system is homogeneous in energy, or equivalently, that it has no proper time ...