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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Combination of quantum numbers for a particle in a 3D box

For a second excited state, the three combination of quantum number corresponds to $$n_{1}=2,n_{2}=2,n_{3}=1$$ or $$n_{1}=2,n_{2}=1,n_{3}=2$$ or $$n_{1}=1,n_{2}=2,n_{3}=2.$$ This is from the text ...
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129 views

Is the energy always discrete?

In the von Neumann axioms for quantum mechanics, the first postulate states that a quantum state is a vector in a separable Hilbert space. It means it is assumed the Hilbert space has a basis with at ...
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Is a Battery to store photons possible?

@MISC {55768, TITLE = {Why can't we store light in the form of light?}, AUTHOR = {AldCer (http://physics.stackexchange.com/users/20409/aldcer)}, HOWPUBLISHED = {Physics Stack ...
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What is the form of energy that is forming while i am holding a suitcase an not moving at all [duplicate]

If I am lifting a heavy suitcase and I am not moving at all. Abviously I am not doing work because I am not moving or rising the suitcase up and down. But abviously I am losing chemical energy since ...
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2answers
55 views

How much energy could be obtained by freezing water?

I know with our current technology energy is required to freeze water. But if the theories are correct we should be able to freeze water by extracting energy correct? How much energy could be ...
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0answers
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What is the form of energy that is forming while lifting a suitcase [duplicate]

If I am lifting a heavy suitcase and I am not moving at all. Abviously I am not doing work because I am not moving or rising the suitcase up and down. But abviously I am losing chemical energy since ...
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2answers
141 views

Question about distillation

I have got a question about distillation. In distillation as we know the mixture is boiled and the mechanism then goes like substances with high boiling points condense at the bottom and substances ...
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0answers
42 views

Does it take energy to destroy the surface of a liquid jet? [closed]

Imagine we have a collision of a liquid jet with an obstacle Does it take time for the surface of the jet to be destroyed while collision?? Or it'll be destroyed immediately?
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1answer
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Does scanning a lightsource affect the scan result?

I'm very much a layman on this kind of topic, so my logic may be wrong, but here goes: Sample situation A 'pass app' on your smartphone, allowing someone to scan your ticket on your device. My ...
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2answers
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If you lift something does the internal energy increase or remain unchanged?

So change in internal energy $\Delta U = q + w$; so in lifting an object you do work on it, thus increasing its internal energy. Is this correct? Sorry if this is a stupid question.
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Does a man run a same distance with different velocities spend the similar energy?

To simplify the question we assume the same man run on a straight and flat road with constant speed. Personally I don't believe the man would spend a similar energy. But how to prove it in physics? I ...
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265 views

Motion in a time-dependent uniform magnetic field

Suppose you have an infinite solenoid generating an uniform magnetic field inside. The field is oriented along the solenoid axis : unit vector $\vec{\bf n}$. The field intensity varies linearly with ...
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Candles: paraffin and flameless, which is the most environmentally friendly?

How could one compute (at least the scale of order) the well-to-flame energetic cost of a paraffin wax candle burning one hour (including CO2 and CO)? Can it be compared with a flameless candle (LED ...
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3answers
125 views

What is physical significance of energy?

John Rennie said, actually all particles are basically energy in the sense that they were created by adding energy to a quantum field. This applies whether you're creating a photon, an ...
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Diffraction of rays [duplicate]

To all the physics experts here this might sound like a stupid question, but I give it a try: This is a sketch of how you usually learn about the effect of diffraction in an experiment: Now I was ...
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2answers
63 views

What is a qualitative description of energy? [duplicate]

In elementary physics courses one is taught that energy is a measure of an object's ability to do work (this in itself seems a little flaky as how does one then define exactly what "work" is, other ...
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4answers
512 views

Do all forms of energy have the ability to do work?

According to this definition of energy: it is the ability to do work. That is $F×s$. But except for K.E. and M.E, no other energy form can do work. So why is this definition in Physics? Lets take an ...
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6answers
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How is momentum conserved when is is only dependent on mass and velocity, and so many other factors come into play?

I've been trying to get a good grip on the difference between conservation laws. Momentum is particularly tricky, I don't understand how quantities like $m\mathbf v$ can be conserved when other things ...
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1answer
36 views

Calculate the applied force associated with uniform distortion of an area

I am exploring Hooke's Law and considering how it might apply to an arbitrary area (perhaps as a slice of some volume). Since $$ F = -kx $$ Would it be correct to calculate the force, $F$, ...
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0answers
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Solving question from a energy perspective [closed]

Im having some trouble with a question i was given for homework. Ive already solved it from a motion perspective but now i need to solve it from a energy perspective. The question states that from a ...
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0answers
64 views

Theta-parameter vacuum energy

Suppose we have $\theta$-field in QCD (in a special case of constant $\theta$ it reduces to ordinary $\theta$ parameter): $$ \tag 1 Z_{\theta} = \int D[\psi_{QCD}]e^{iS}, $$ where $$ \tag 2 S = \int ...
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1answer
105 views

How are these marbles being accelerated?

This question refers to an effect visible starting at around 5m45s in this video1. (The question will make little sense if one has not first watched the clip.) The observation At around 5m45s we ...
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2answers
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Work done changes between reference frames?

(This is not homework; a friend shared with me this puzzler and neither of us can figure it out.) Suppose you are in a plane traveling at velocity $v_1$ relative to the ground. The flight attendent ...
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1answer
50 views

Fundamentally speaking, what are all the essential factors for waves (of any nature) to exist?

Considering all systems in which waves can exist, from atomic scale (such as DeBroglie Waves for example) to cosmic scale (gravitational waves for example), and those that require media for transport ...
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2answers
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Travel by Earth rotation [closed]

why we can't go outside the atmosphere and travel with earth rotation .. and can we travel in the opposite direction of atmosphere by the same speed of atmosphere it’s moving at about 1,000 miles an ...
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3answers
38 views

Hot Chocolate- cooling itself down

If a hot cup of hot chocolate is just standing there, can it cool itself down by transferring the kinetic/thermal energy that the liquid has into the mug/cup?
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1answer
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Could one, practically or hypothetically, capture energy from heat using magnetic fields? [closed]

I have had this idea, and I'm not sure if it would work. Heat is a form of chaotic kinetic energy, right?. Would it be possible to create a magnetic field within a gas or liquid so that when the ...
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2answers
46 views

Tension at topmost point of a vertical circle

I read that for a body to move in a vertical circle, the minimum tension needed is 0 at the topmost point. Can someone explain to me what it means to have positive or negative tension on top. I'm not ...
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1answer
46 views

Can we transfer energy wirelessly?

Now-a-days solar energy is good alternating source of energy and it is free without any harmful effect to our environment. But earth based solar energy systems are dependent on a major factor, which ...
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1answer
115 views

Energy/entropy in transport of molecules across cell membranes

I'm asking a "Maxwell's Demon" question. I've read statements that sorting molecules and sending them to one side or the other of a barrier requires work, but none of these statements have explained ...
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4answers
78 views

Why do coal power stations not directly use combustion to turn the turbines?

Why do coal power stations run by creating steam rather than from the expansion due to combustion? I understand that in order to generate electricity in a coal power plant, steam is usually produced ...
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0answers
17 views

Do we have the potential technology to harness the energy the Earth is constantly giving us? [duplicate]

Messing around with fun physics, and it got me thinking. I probably am not the only or the first one to think of it. I am wondering what more experienced physicists on this site can contribute to this ...
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1answer
25 views

How is work constant when I raise a body to a height?

My friend asked me- Imagine that we pull up a pen which is initially at the ground slowly upwards.At a certain point we see that its total energy is due to its P.E.So,how can we say total energy ...
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1answer
38 views

Internal energy of a body

I have a really fundamental question regarding the internal heat energy of a body. From textbooks, we know: $$\Delta Q = m \cdot c \cdot \Delta T$$ where $m$ is the mass of the body, $c$ its specific ...
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1answer
84 views

Energy of a permanent magnet railgun

I'm creating a permanent magnet railgun, which essentially uses two conducting rods with a row of magnets between them and a conducting projectile laying across the two rods. I am trying to determine ...
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2answers
264 views

Mass hanging from spring: potential energy [closed]

I have encountered a problem with a mass $m$ hanging from a spring. I want to find the maximum distance it will be stretched from the spring's equilibrium. At the maximum distance the spring is ...
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0answers
56 views

Why on a frictionless incline, a rolling object reaches the bottom slower than an non-rolling object?

I am really sure if what my physics teacher told me was correct. But he said, rolling objects has rotational kinetic energy, so not all potential energy they have at the start is converted into ...
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37 views

Kinetic energy formula from nonzero initial velocity

Do I then have to use: $$\frac{1}{2}m(V_f^2-V_i^2)$$? I am assuming I should use this formula for change in kinetic energy if the object under examination doesn't start from rest.
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1answer
81 views

What form of energy is magnetism stored in?

In physics class I was told that there are 9 forms of energy: -Electrical -Light -Thermal -Nuclear -Elastic Potential -Gravitational Potential -Sound -Kinetic -Chemical So, my question is, ...
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1answer
97 views

How much work can the human body do before dying of exhaustion [closed]

If we could assume: We don't increase our energy from absorbing food. Our human example in scope isn't starving or suffering from malnutrition. I mean how much work can we do until the body would ...
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2answers
53 views

Inconsistency with electrostatic energy formulas

The energy of point charge configuration can be written as: $$W = \frac{1}{2}\sum_{i=1}^{n}q_{i}V(r_{i}) \, ,$$ which can take both positive and negative values. However, when we integrate the ...
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1answer
44 views

Plausibility of the distance estimation in a cycle ergometer gym exercise

A friend of mine pedaled for an hour on a cycle ergometer, a stationary bicycle in a gym. At the end of the ride the cycle computer reported a distance of $40\:\mathrm{km}$ and an average power of ...
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0answers
81 views

Will the block #3 move? [closed]

Hey, On my test I've been assigned to calculate acceleration of the box with mass = m3(I'll call it block #3). The problem is, I can't even imagine the block moving, as I cannot find any force ...
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0answers
85 views

Formulae for Elastic Hysteresis of rubber

Being a school student, I'm pretty sure we don't need to explicitly learn any formulae helping us evaluate the energy dissipated by mechanical internal energy in a hysteresis loop. But I was wondering ...
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1answer
35 views

Kinetic energy of fluid + collision

When a fluid is flowing, it has of course a kinetic energy and thus we can define kinetic power equal to ρAv v is the velocity and A is the surface of a solid for example. I have a question (maybe it ...
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1answer
24 views

Reverse particle accelerators! [closed]

If we are tearing matter apart in accelerators, why can't they reverse the process? Apply energy at one end and take matter out of the other. When energy first changed to matter in the Big Bang, ...
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1answer
41 views

Kinetic energy during 1 minute - wrong? [closed]

I've come across this IEEE paper whilst researching for a project I've undertaken regarding a bicycle generator. This paper concerns an exercise bike powered electric generator. Essentially they have ...
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1answer
88 views

Why are harmonic oscillators quantized? [closed]

What physical reason is there for a mass on a spring to have discrete energy levels? And why are those energy levels equally spaced, i.e. why is $E \ \alpha \ f$? Personal background and ...
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Does matter shrink due to energy radiation and does it have anything to do with dark matter and dark energy?

Is matter shrinking? Is shrinking the cause of concentrated dark matter that makes up matter moving from concentration to unconcentration. Does dark energy and expansion of the universe come from this ...
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1answer
31 views

anatomy of combustion

I don't understand how energy is released in combustion. We have a reaction of a combustible material with oxygen and this releases energy. In what form is this energy released? It should be some ...