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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Why does water not evaporate in below 0 degrees?

I have learnt that, most objects still have energy in their atoms until the temperature reaches absolute zero. In other words, everything has energy around us. Now, that in mind if I go to antartica, ...
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1answer
52 views

Would half of electromagnetic wave be absorbed on first sensor?

If I would set up electromagnetic emitter that would emit one wave, but while it would be emitting it I would spin emitter 180 degrees at such speed that one half of wave would be emitted in that time ...
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1answer
753 views

Is it possible to generate electric energy from the radiation of radioactive materials

I wonder if it is possible to generate electric energy from the radiation of radioactive materials like nuclear waste? If it is then wouldn't that also mean that it could be used as an energy source ...
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2answers
352 views

Can diffusion produce energy?

A friend and I recently got into a silly argument where I stated pure diffusion can't produce energy since diffusion are a part of passive transport. He stated if we If we have tinny ...
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4answers
285 views

what property of steam makes it the preferable motive fluid in jet ejectors? why not air or nitrogen?

I want to know what properties of steam make it the fluid of choice in steam turbines jet ejectors. I want to understand the mechanism of energy conversion in these equipment and hence understand ...
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2answers
2k views

Why isn't water running faster hotter?

I was running the washing up water this morning, and started to think about why the cold tap isn't hot, and why the water doesn't get hotter the faster it is flowing (if anything, the cold tap gets ...
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2answers
697 views

Conservation of energy in transformers

How does energy remain conserved in a transformer if emf is increasing, or decreasing? Does the current decreases to accomodate? Does Ohm's law still hold here? Although we know, Ohm's law is not ...
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4answers
57k views

What is the relationship between Force and Kinetic Energy?

I am an Middle-School (Grade 8) student, who is self-learning classical mechanics. I saw this equation from Classical Mechanics: $\vec F=m \vec a$, the following equation is pretty straight forward ...
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2answers
92 views

What is the energy operator and from where do we get it?

I am trying to learn Quantum mechanics from MIT OCW Videos about quantum mechanics. I have reached the 5th lecture. Please help me in understanding this: In the middle (At 32:08), the professor wrote ...
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1answer
32 views

Is watt unit depended on turbine speed

I'm new to electronics. I have a doubt. That is... Is watt unit depended on speed of turbine ? In my mind When turbine rotates fast the power in increase. Is it right ? Please help me. Thanks for ...
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1answer
55 views

Why is work not related to velocity?

A very simple question; why does it cost me more energy to very slowly lift a mass $m$ over my head compared to very fast? The definition of work does not state anything about velocity, only the ...
5
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1answer
255 views

What does the Higgs boson have to do with the uncertainty principle and quantum oscillations?

I was looking in New Scientist the other day when I saw something to do with the Higgs boson, energy levels, entropy, space/time, quantum oscillations and many other things. It was in a feature to do ...
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2answers
136 views

Energy of damped harmonic oscillator begins to increase with very large Q in numerical integration

I have numerically integrated the (reduced) homogeneous equation of a damped harmonic oscillator in order to see how the error propagates. $$\frac{d^2 X}{d\phi^2} + \frac{1}{Q}\frac{dX}{d\phi}+X(\phi)...
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5answers
3k views

How badly could someone be injured by concentrated sunlight?

Recently-ish, I stumbled across an interesting short story (by way of Science Fiction & Fantasy Stack Exchange) where a soccer referee is apparently incinerated by concentrated sunlight. Where ...
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3answers
8k views

Does an object's kinetic energy increase, decrease, or stay constant when it reaches terminal velocity while falling?

Does an object's kinetic energy increase, decrease, or stay constant when it reaches terminal velocity while falling?
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1answer
206 views

Conservation of energy and the 'crazy ball' product

Well I'm not sure how many people remember the crazy ball - a small ball made of rubber which bounced like crazy. What I noticed is that the ball seemed to bounce higher than the point from which it ...
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1answer
175 views

Energy density and Carnot cycle

For example, diesel has about 40 MJ/kg, what does it mean? Is that if we burn it we will get 40 MJ of energy per kg, but we can not get all of it to mechanical work? If that is the case, then why can'...
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2answers
189 views

Does the Night Mode of the screen display (LCD) save more energy? [closed]

In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display. LCD(Liquid-crystal display) seems to be ...
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2answers
405 views

Why do electricity generators have to work harder for higher loads?

Maybe this is a silly question, but why does, say, a gasoline-powered AC generator have to use more gas depending on the load? Let's say I have a 120VAC generator and either a 1A or a 10A load, and ...
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4answers
2k views

Why do we need high energy to explore small dimensions?

I am taking a quantum physics class, and for the life of me, I can not remember why we would need a vast amount of energy to understand the microscopic universe.
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0answers
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Building free energy directly from lagrangian

Energy can be built from lagrangian when considering the symmetry of time $(\frac{\partial L}{\partial t}=0)$. Free energy is a generalization of energy when the system exchanges heat with the ...
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2answers
109 views

Calculating Quantum number from initial conditions

I have solved the particle in a box problem to get energy eigenstates and wave vectors: $$E_{n}=\frac{\hbar^{2} k^2}{2m} ,\hspace{1cm} k_{n}=\frac{\pi n}{L}$$ And now I am trying to figure out how ...
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2answers
82 views

Energy of an EM Wave and its temperature and amplitude

I'm trying to understand why classical physics fails to explain black body radiation. I'm confused. According to Boltzmann, energy calculation for em wave is based on temperature. According to ...
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1answer
106 views

Spacetime and the conservation laws

I'm reading Peter Atkins' book, Galileo's Finger, and in the chapter on energy, he makes the points that the conservation of momentum stems from the shape of space (that it's smooth and not lumpy) and ...
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7answers
1k views

How does heat actually stay kept in the carbon molecules in the atmosphere? [duplicate]

We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat. However, how is heat actually kept in those molecules. When photons heat them up, their ...
0
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1answer
137 views

Aside from Noether's theorem, what other concepts would explain energy conservation?

Energy is defined more in the mathematical sense, and tends to show true with observations in the physical world. But why is energy conserved aside from "Noether's theorem"? In a closed system that ...
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4answers
1k views

Will a water-cooled system heat up a room less than an air-cooled system?

Recently - motivated by the recent heat where we live - an acquaintance argued that a water cooled computer will not heat up the room as much as an air cooled computer will. His reasoning was that the ...
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1answer
50 views

Power delivered by a plug

Ok so i know that (in the UK) the voltage of a mains supply is 230v. But when we plug a item e.g. a tv in to it what determines how much power is drawn from this supply. I presume it is the current ...
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0answers
33 views

Thermodynamics of binary symmetric channels

I am reading this very interesting paper: http://m.iopscience.iop.org/1751-8121/41/40/402002/pdf/1751-8121_41_40_402002.pdf about thermodynamics of channels in information theory. More generally, ...
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2answers
674 views

Ground state of a quantum mechanical system

When looking back at my courses of quantum mechanics, I noticed that assumptions about the ground state of a quantum mechanical system where rather vague and unprecise. It is always assumed that a ...
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1answer
42 views

is it possible to change the energy of a waveform like radio wave & turn it into microwave?

In the electromagnetic spectrum, the differences between all waveforms are the "frequency" & energy of the waveform. We are able to modify both of these parameters. So, is it possible to change ...
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1answer
124 views

What would happen in a collision of an antimatter singularty and a matter singularity? [duplicate]

Would energy be released if a black hole made out of antimatter and another of matter were to collide?
2
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1answer
446 views

Does negative energy density (i.e. weak energy condition violation) create closed timelike curves?

I remember reading something about Stephen Hawking denying the fact you can't make CTC's (Closed Timelike Curves) without weak energy condition violation. If this is true, where do the light cones ...
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3answers
841 views

Of all the electrical energy used in a home, is there any portion that won't eventually become thermal energy in the home?

Considering all of the appliances that the average home uses--microwaves, light bulbs, dishwashers, refrigerators--is it safe to say that all of the electrical energy in a home will be converted to ...
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1answer
1k views

Storing kinetic energy instead of potential energy - practically possible?

One of the big problems today considering energy is its storage (e.g. batteries are not that efficient, very expensive and polluting). Energy is classically mostly stored as some kind of potential (in ...
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4answers
960 views

Bouncing ball time problem

I'm studying a problem and I encountered a strange problem: When a ball bounces how much time does the ball spend while touching the floor? To be more clear I suppose that when a ball bounces ...
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4answers
758 views

What is the correct term to describe matter converting into energy?

Matter and energy are related; one can convert into the other. What is it called when this happens? For example, solids melt/liquefy into liquid, and liquid vaporizes into gas. Gas condenses into ...
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0answers
57 views

Energy of a system

I'm considering a ring of mass $m$ sliding along a cardioid with equation $r=a(1+\cos\theta)$. We let the angle between the downward vertical and the radius vector be $\theta$. The ring is attached to ...
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1answer
93 views

Observation of light bending spacetime [duplicate]

Has radiation or energy bending spacetime ever been observed? If not, is it likely that it ever will, assuming current technology? Note: This is not a question of space bending light, but of light ...
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2answers
343 views

Speed of gravity

Consider two objects presented in the figure below. Objects have equal masses and are separated by a distance of 60 light seconds. Assume that we move left object by 3 light seconds to the left in ...
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3answers
15k views

Is it more efficient to stack two Peltier modules or to set them side by side?

Is it more efficient to stack two Peltier modules or to set them side by side? And why? I have a small box that I want to cool down about 20 K below ambient -- cold, but not below freezing. (I want ...
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1answer
88 views

What's wrong with this simple derivation of energy flux in a photon gas?

In a photon gas, we know that pressure, $P$, and energy density, $u$, are related by: $$P=\frac{u}{3}$$ We also know from relativity that the momentum of a photon is $$p=\frac{E}{c}$$ Finally, the ...
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4answers
336 views

Do magnets redshift light?

Do magnets redshift light? Suppose we have an extremely powerful magnet (say the size of the Sun) and we have a smaller paramagnetic material above it (say. Titanium Brick which is indestructible)...
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1answer
237 views

Does the Alcubierre drive use negative energy to compress space infront of it?

The contraction in most images looks like a gravity well. Is it that you use negative energy to BOTH contract and expand space or positive and negative to contract (positive energy) and then expand ...
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4answers
1k views

What does the work on a current carrying wire in a Magnetic Field?

We consider that the force acting on a current carrying wire placed in a uniform magnetic field perpendicular to the length of the wire is given by $IBl$. If the wire moves by a distance $x$ in a ...
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4answers
878 views

Definition of force, kinetic energy and momentum

I've edited the post. Q1 and Q4 are the important ones but I didn't delete Q2 and Q3 since some older answers would not make sense anymore. To begin with, the formula of the kinetic energy $T$ is $\...
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1answer
459 views

Unstable states and imaginary (complex) energy?

I came across the notion of complex energy while studying instanton method to study the unstable state. Unstable states are those which have energy with an imaginary part. But as we know Hamiltonian ...
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1answer
65 views

How do you calculate the energy output if you know the volts, amps and time? [closed]

How do you calculate the energy output if you know the volts, amps and time?
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1answer
322 views

How would one compute the angle of deflection, in a relativistic collision - underspecified system?

Consider the simplistic case of two identical mass particles colliding elastically with the second particle initially stationary and the first particle travelling with energy $E$. By conservation of 4-...
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4answers
6k views

Is it possible to create matter? [duplicate]

Is it possible to create matter? In a recent discussion I had, it was suggested that with enough energy in the future, "particles" could be created. It seems like this shouldn't be possible due to ...