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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Energy on Voltage-distance relation of Gas Electron Multiplier (GEM)?

I am thinking if there is any single graph which could somehow visualize the energy in relation to the GEM schema. So I selected the voltage-distance relation, V-r, in Figure b) in relation to the ...
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52 views

Fusing Hydrogen with lightning

I've been reading about fusion recently (Specifically Deuterium fusion) and a friend of mine asked me if it was possible to fuse two Deuterium atoms with a lightning strike? Now this question has a ...
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2answers
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Why is light energy 100% reflected in total internal reflection?

during reflection of light energy transfer is not 100%. when light from a rarer medium like air strikes a denser medium like glass slab, some part of light is reflected back and some of it is ...
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1answer
42 views

How would the angular velocity of the rod change if it slipped on the table?

I wanted to consider a second case of my homework assignment. We were asked to solve the question: A uniform rod of length b stands vertically upright on a horizontal plane in a position of unstable ...
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70 views

How can we produce gasoline with nuclear fusion and without fossil fuels? [closed]

If all fossil fuels were suddenly to run out tomorrow, but we also were to discover an easy way to produce energy from nuclear fusion, how might we produce gasoline? Could we do it in a way that is ...
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1answer
68 views

Can more than one photon be in the same space as another photon?

I have heard light described as a particle that travels in a wave. I have heard that waves are unique in that two waves can take up the same space as they are travelling, either through constructive ...
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0answers
27 views

What is the more fundemental form of energy denisty for electric field?

This question is related to Energy density with complex permittivity? (in that I think answering this will also answer the linked question). What is the more fundamental form of energy density for ...
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4answers
166 views

Energy density with complex permittivity?

Question What is the correct form of the energy density when we have a complex permittivity (such as in a dielectric)? Additional information A complex permittivity means that we have: $$\vec ...
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1answer
93 views

Can the de Broglie wavelength become infinite?

i am new to the concept of de Broglie wavelength. We all know that $\lambda=\frac hp$ and $E_\text{kin}=\frac{p^2}{2m}$ implies $p=\sqrt{2E_\text{kin}m}$ and therefore ...
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37 views

two sphere collision, distribution of KE

If we have two glass balls of exact same mass and size. We tape to the first one a very little piece of titanium facing the other sphere and we collide the two spheres at the same speed. The question ...
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2answers
56 views

What is the mechanism of heat exchange of a bouncing ball?

Imagine a falling ball on a perfectly hard ground. The kinetic energy will be first converted into a deformation of the ball, then the ball will restore it into kinetic and heat energy and recover ...
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2answers
90 views

The work done by a spring over a specific distance

I cannot seem to find the answer for my question. I know that the formula for work is $W = FD$. Given a mass that is attached to unstretched spring and is pushed by some force to stretch the spring, ...
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25 views

How to compute the speed of a cosmic ray from its energy? [duplicate]

How can you compute the speed of a cosmic ray from its type and measured energy? For example, if a cosmic ray were said to be a proton of 10 GeV, how would you compute the velocity of that cosmic ...
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1answer
52 views

How can I get the energy levels from a Hamiltonian?

I'm helping out in a research project at my school and was tasked with plotting the magnetic field dependency (when B is parallel to each individual axis) of the energy levels of the molecule with ...
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3answers
186 views

Why does the work-energy theorem need to include internal forces?

Can anyone kindly explain me why work energy theorem must also include internal forces? The proof of work energy theorem is derived from Newton's laws of motion, but Newton's laws of motion don't ...
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2answers
85 views

What's the right way to calculate power consumption over a month given a rate per minute?

When I was searching for power required to lift an object, i found that, for example: $100\ \mathrm{kg}$ to be lifted 3 metres in 5 seconds. (vertical) Answer: $$\begin{align} ...
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1answer
25 views

Can different energies be merged to “create” new kinds of energy, with respect to mass and energy conservations?

If energy and mass are the same thing, and matter which has mass -- chemicals to be exact -- can be combined to make new chemical compounds, can the same be done to energy? If so, how would it be ...
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17 views

Magnetic harvesting

(I asked a question earlyer and then I realized that I had worded it in the wrong way so I am going to try again) so I was wonder if it was possible to harvest the magnetic energy from a permanent ...
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0answers
32 views

EM wave frequency and photon energy

We know that a quanta of light of frequency f has energy hf. But when I consider a single photon there is no concept of "frequency of a wave" because there is no EM wave associated with it which ...
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1answer
35 views

Counter intuitive temperature readings in my HRV unit (heat transfer)

Based on temperature alone, it appears that I'm gaining more heat than losing in my HRV. What I'm seeing is the warm air leaving my house dropping by 10C, and the cold air coming in rising by 12C. It ...
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1answer
31 views

How does a nozzle behave differently at different velocities of flow?

A converging duct acts as a nozzle for subsonic flows while the same nozzle acts as a diffuser (decelerator) for supersonic flows? How does this actually work?
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2answers
150 views

A Question on Bohr's model of atom [duplicate]

When an electron revolves around a nucleus, It uses its energy in form of kinetic energy and so it release energy and then moves . It means that it release energy continuously, Otherwise, if it does ...
2
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1answer
42 views

Why does the Gravitational Potential energy formula indicate that heavier masses in the same point in the field have lower potentials?

$$ U = -\frac{Gmm_E}{r} $$ Intuitively, it'd appear that the further away two objects are, the greater their gravitational potential, and this is confirmed by the gravitational potential formula. The ...
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1answer
40 views

What is the main difference between a free particle on a line and a free particle on a circle?

The energy spectrum for a free particle in a circle with radius $r$ is $$E_n=\frac{n^2\hbar^2}{2mr^2}.$$ The energy spectrum for a free particle on an infinite line is similar. If so, what is the ...
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2answers
321 views

Where does a hadrons mass come from [duplicate]

So I've come to the understanding that a hadrons mass does not come from the constituent quarks but instead comes from a combination of things like binding energy and the mass energy of virtual gluons ...
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1answer
61 views

How to calculate the increase in temperature due to drop? [closed]

Question- Calculate the rise in temperature in celcius in a bucket of water after it is dropped from 50 m where acceleration due to gravity is 10. I know that I need to find the amount of energy ...
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1answer
41 views

Energy from 10% of stars in Galaxy over their lifetime [closed]

I heard an assertion that referred to the 'energy from 10% of stars in our Galaxy over their lifetime' on Radio 4 Inside Science and wondered if it is possible to estimate/calculate the energy value. ...
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1answer
95 views

How much energy would be required to make one tea cup full of Earl Gray tea at 100F?

On the TV show "Star Trek: The Next Generation", Captain Picard is often pictured using a replicator to materialize a cup of "Earl Gray tea, hot". Besides wondering what they do with all the empty ...
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4answers
134 views

Why the electromagnetic waves propagate and do not stand still?

I know that the electromagnetic waves are alternating electric and magnetic fields. But I don't get why they can't stand still and alternate at the same point. I would like a logical and verbal ...
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1answer
38 views

What mechanism can we use to convert waves energy?

In term of renewable energy, can we use waves as another energy that can be stored and used instead of solar, wind and etc ? What I mean here is not sea waves but another kind of waves such as radio ...
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1answer
25 views

Heat, Work and Internal energy in closed systems

This has been troubling me for a while now. I know that the performed work equals $P\Delta V$ for isobaric systems and I know that in isochoric systems no work is done, but how do I find the heat $Q$? ...
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3answers
67 views

Using Gravity for Infinite energy?

Can gravity be used as an infinite energy source? What if you throw objects down, say a hill, and had a panel on the bottom that would use the force of the fall and convert it to energy? Would this ...
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0answers
28 views

How efficient is the forward transfer of energy in gravity (surface) waves?

Ocean waves (properly categorized as gravity waves since gravity provides the restoring force within the medium they travel) propagate the major part of the energy derived from winds along the ...
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1answer
58 views

What are negative and positive energies? [closed]

So I have a few questions related to the negative and positive energy topic. 1)What do we mean by negative and positive energies in physics? 2)I have seen in a minute physics video that we need ...
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19 views

What Happens When 2 particles Touch [duplicate]

Lets take two uncharged particles namely A and B . If these two particles touch each other what are the energy changes that could occur on both the particles. Also when the process of Touching is ...
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1answer
77 views

A Confusion About Energy-Time Uncertainty Relations

In all the textbooks that I have seen, energy-time relation is written in the following way:$$\Delta E \cdot \Delta t \geqslant \frac{\hbar}{2}$$ Here is my interpretation of this principle: The ...
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1answer
42 views

Deexcitation times for ytterbium

I need to find the deexcitation times for the transitions found in Figure 1 of Nature Phys. 8, 649 (2012), arXiv:1206.4507. That is, what is the deexcitation time for the following transitions: $$ ...
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1answer
107 views

How are the watt-second, the newton-meter and the joule different?

The joule is $\mathrm{kg\,\ m^2/s^2}$ right? The watt-second is $\mathrm{J/s} \times \mathrm{s}$ thus $\mathrm{J}$. The newton-meter is $\mathrm{kg \,\ m/s^2} \times \mathrm{m}$ thus $\mathrm{kg \,\ ...
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2answers
233 views

Change in internal energy is 0 in isothermal process

I am having trouble understanding why in an isothermal process, the change in internal energy is zero. I know that $\Delta U$ or $\Delta E=q+w$, and so in isothermal process $q=0$. But how does one ...
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1answer
86 views

Are quantum “virtual negative-energy particles” the same as “negative energy density” in EFEs?

Question is fairly straightforward. Quantum theory describes negative energy in the form of the Casimir effect and virtual negative energy particles. In the Einstein field equations, negative energy ...
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1answer
47 views

Work and energy question

An athlete picks up a $20.0\,\mathrm{kg}$ sandbag from the ground and throws t straight up in the air. It leaves her hands $1.50\,\mathrm{m}$ above the ground and reaches a height of ...
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2answers
83 views

Can I define the term energy in terms of work?

Recently, I'm doing my personal task which is to formalize every definition and concept in physics, by means of formal language and of course with intuitional notes. Because I found myself that the ...
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1answer
62 views

Are energy levels specific to certain atoms?

For such a simple question, I cannot find an answer anywhere. Are the energy levels specific to each atom? For example, is the energy required to jump from the first energy level to the second energy ...
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1answer
19 views

The speed of an electrical signal through different mediums [closed]

This is sort of a bio physics question and it comes in two parts. The first is: what is the speed of an electrical signal through human nervous tissue? The second part is: what is the speed of an ...
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1answer
71 views

Would it be safe to say that mass is kind of a property of energy?

In a video i just saw about the true meaning of E=mc2, it said something that really got me thinking; "Mass is not really converted to energy" and that mass wasn't actually a thing, but more of a ...
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2answers
81 views

Why is kinetic energy calculated using speed?

Why is kinetic energy calculated using speed? Since speed is distanced covered, and if a car moves 100 meters around a circular track -- stoping after moving half of the distance of the track -- the ...
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0answers
41 views

How much damage do high energy experiments impose on the LHC detection equipment?

I do appreciate that I am second guessing lots of experts who have already considered this aspect of high energy experimentation, but I have not seen a similar question, my apologies if I missed a ...
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1answer
92 views

How to calculate how much energy a body gets from a star?

Okay, so I could swear that I've seen an equation before for this (which I believe involved the Stephen-Boltzmann constant.) But now that I actually need it, much like my reading glasses I can't seem ...
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1answer
61 views

Contradiction of total energy of a system? [duplicate]

I consider a situation in a system in which an observer is sitting in body of mass $M$ and another observer in a body of mass $2M$, both moving with velocity $v$ towards each other. If observers in ...
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1answer
182 views

Is work energy theorem $W=\Delta K$ or $W=\Delta E$?

I know that work is the change in kinetic energy. I saw on an equation sheet that work is equal to the change in total energy. Is this true? If so, how?