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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Producing energy with entanglement

If we entangle two electrons for example and move one of the electron to Mars for instance. Are we able to somehow transfer the kinetic force of Mars from its movement (spinning and orbitting) to ...
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118 views

Explanation of force amplification inside a solenoid

For a system being actuated by a motor, the force can be amplified by gearing. The energy is being used for force instead of distance, so it produces more torque but moves slower. For a system being ...
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2answers
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Water Electrolysis Calculations

From Wikipedia (http://en.wikipedia.org/wiki/Water_electrolysis#Efficiency): The electrolysis of water requires a minimum of 237.13 kJ of electrical energy input to dissociate each mole. Each ...
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Why are force, momentum, and kinetic energy derivatives of each other [closed]

Force $ma$ is the rate of change of momentum, or the derivative of momentum with respect to time $$\frac{d}{dt} mv = ma = F$$. Kinetic energy is the integral of momentum with respect to velocity: ...
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What is the free energy of an ideal chain under stress?

this question is related to potential energy of a segment of an ideal chain under external force. I calculated the canonical partition function for an ideal chain ($i$ stands for a single segment ...
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2answers
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Having trouble understanding the work energy principle intuitively

I'm having trouble understanding the work energy principle intuitively. This is what I'm solid on so far: If you have a ball rolling down a hill, it loses potential energy and gains kinetic energy. ...
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Why do particles in a medium have different speeds?

If thermal conduction occurs because of particles colliding with each other and imparting kinetic energy to each other, won’t the particles of an isolated medium collide with each other until the ...
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3answers
565 views

Would sea water moderate a nuclear submarine meltdown?

My son asked me: If nuclear submarines get sunk or blown up, what is to stop them going into nuclear meltdown? I thought about it and came to the conclusion that because they're in the sea the ...
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1answer
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Proportionality constant in crater equations

I have searched for equations regarding craters and I came across two of them. The first one is from this NOAO website in the level two section. There, it says that, $$ D^3\propto E $$ where $E$ is ...
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4answers
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What exactly is work?

What exactly is work? My book confuses me: a force can lift an object to a height h, or it can accelerate an object through gravity. In all these cases, a force displaces an object and change the ...
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3answers
72 views

A block sliding down a ramp lab (with friction), I keep getting a higher final energy than initial

A block of 55 g is sliding down a ramp of 35 degrees of inclination. The hypotenuse of the ramp is 63 cm and the height is 36 cm. vi = 0 as the block starts at rest. I did 3 trials of letting the ...
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4answers
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How do electrons get the energy to jump from one orbital to the next when in stationary orbits the electron does not radiate energy

My Question is how do electrons get energy/lose energy to jump up or down an orbital as in a stationary orbit they do not gain energy and their energy is finite?
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How is energy dissipated in a travelling em wave

How is energy dissipated in a travelling em wave. Will there be any dissipation if it were to travel trough vaccum ?
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Work-energy theorem? [duplicate]

The initial kinetic energy of an object moving on a horizontal surface is K.Friction between the object and the surface causes the velocity of the object to decrease uniformly to zero in time,t.How ...
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0answers
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Work energy theorem problems [duplicate]

The initial kinetic energy of an object moving on a horizontal surface is K.Friction between the object and the surface causes the velocity of the object to decrease uniformly to zero in time,t.How do ...
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2answers
35 views

What is the work done?

A painter uses 1.93kJ of mechanical energy to pull on the rope and lift a 20kg paint barrel at constant speed to a height of 7.5m above the ground. How much work was done lifting the paint barrel? ...
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3answers
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Is work-kinetic energy theorem useless?

This is how my book explains it: $W_{net} = \delta K$ Since the net work is tied to changes in kinetic energy and changes in speed, a mass must accelerate in order for net work to be nonzero. ...
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2answers
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Is Information a potential or kinetic kind of energy?

It is said that the law of least action is that nature tries to convert potential energy into kinetic one as fast as possible. Information can't be thought without a physical realisation, see here. ...
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2answers
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Electric Potential Between Two Like Charges

At the point horizontally across and equidistant from the centers of the two charges (also oriented horizontally), what is the electric potential? At that point, the electric field of the first charge ...
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1answer
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Lennard Jones Total system energy [closed]

i am trying to implement/extend an implementation of Lennard-Jones potential simulation regarding Xenon molecules (for curious ones, the code can be found here functions (force_naive->lj_force)). ...
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2answers
112 views

Energy spent climbing a flight of stairs

I would like to know whether there is any difference in the energy consumed in climbing a flight of stairs, if the steps are taken one at a time vs taking them 2 at a time
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1answer
409 views

Sufficient conditions for the energy to be not conserved?

I'm almost embarrased to ask this question because I thought I was by now very confident with classical mechanics. Someone has stated that given a mechanical system with a Lagrangian $L$ s.t. ...
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1answer
53 views

Work done by friction on a ball flying through air [closed]

A baseball of mass 145 g leaves a pitcher’s hand at 150km/hr, but due to constant air resistance, it arrives at home plate 20.0m away traveling at 145km/hr Assume that the magnitude of the ball’s ...
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1answer
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Mutual capacitance upper limit

I am having trouble making an analog for mutual capacitance from mutual inductance. In circuits with magnetic coupling, there is an upper limit established on mutual inductance due to energy ...
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4answers
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Proof of conservation of energy?

How is it proved to be always true? It's a fundamental principle in Physics, that is based on all of our currents observations of multiple systems in the universe, is it always true to all systems? ...
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1answer
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Conservation of energy in a moving frame

I know a similar question has been asked but i'm still kind of stumped. Imagine the earth on the left and a small mass to it's right separated by some distance h. You are in the frame of reference ...
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0answers
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Fictious forces and calculation of energy + c.o.m. question

I am aware that in order for energy to be conserved the reference frame that you are using must be inertial. However, consider the situation where you are using the reference frame of the earth and ...
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How efficient is an electric heater?

How efficient is an electric heater? My guess: greater than 95%. Possibly even 99%. I say this because most energy is converted into heat; some is converted into light and kinetic energy, and ...
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1answer
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Gas Cooled Fast Reactor Coolants

I know that helium and CO2 are used as fast reactor coolants, but how about other inert gasses with low neutron absorption, like argon, why do I see no papers on that? Oh and bonus question. Why is ...
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6answers
162 views

Why it is colder in mountains, at high altitudes?

The conventional answer is to say that "lower temperature follows from lower pressure because temperature is average molecular energy (average speed)". For instance "Temperature is a measure of ...
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1answer
41 views

How to calculate the potential energy of an $H_2$ molecule

From left to right, electron $e_1$, $e_2$ and proton $p_1$, $p_2$. $r_0=0.529nm$ The total energy is sum of energy require to bring each particle to its place. Take the place of $e_1$ is zero ...
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2answers
85 views

Where does the energy go when light is redshifted? [duplicate]

Imagine a galaxy millions of lightyears away and, obeying Hubble's law, moving very quickly away from us. Now imagine the same galaxy emitted a green photon in our direction (a photon with a ...
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6answers
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Why does higher acceleration minimize a car's fuel consumption?

I generally try to optimize my car's fuel consumption when driving, using my car's real-time MPG gauge and average-trip MPG indicator. Until recently, I believed the slower the acceleration, the ...
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0answers
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Cancelling waves and preservation of energy

In quantum physics, a particle is "defined" by a wavefunction. If you would take 2 particles with the same wavefunction, and negate one of them. They would cancel each other other out. Take for ...
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Would impact angle matter on relativistic impactor?

I'm trying to calculate (for fun) a comparison between a kinetic impactor and an H-bomb. I would assume this to be a fairly straight forward problem involving kinetic energy and a table of various ...
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1answer
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What is the Proper way to determine overall velocity in a pipe?

I am running a simulation of fluid in a pipe. The fluid in this pipe is "swirling" (instead of just moving in one direction, it's rotating as well. Like the Helix below. The fluid is faster on the ...
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3answers
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How does The work done in going around any path in a gravitational field is zero implies conservation of energy?

In The Feynman Lectures, Feynman states: The work done in going around any path in a gravitational field is zero. This is a very remarkable result. It tells us something we did not previously ...
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2answers
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Does the speed of electrons depend on energy?

I would like to know whether the speed of an electron depends on energy. If yes then in a circuit when electrons flow out of a resistor the energy decreases by a considerable amount, leading to the ...
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1answer
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does $Q_AV_{AB}=Q_BV_{BA}$ in this case

Sorry fo unclear title but I can't find any suitable on for this question. Here is what my text book says about how to find out the energy of a system of charge of n particle. What I don't know is ...
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2answers
149 views

Factors on which Coefficient of restitution depend

What are the factors on which coefficient of restitution depend? What is the reason for more coefficient of restitution of two glass balls (0.95) than for two lead balls (0.20)?
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Are there other types of energy?

Objects possess potential and kinetic energies. The potential energy depends on the position of the object, while the kinetic energy is dependent on its velocity. My question: are there other types ...
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If conservation of energy was wrong, how would we know about it?

Suppose you just started learning physics and you've been introduced to conservation of energy and kinetic energy. Apart from those concepts you know next to nothing. Then you observe an inelastic ...
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Does an induction cooktop consume as much energy when it's heating something as it does when it isn't? [closed]

If you plug in an electrical charger or an adapter of an electronic device such as a mobile phone or a laptop into the power socket, but you don't actually attach the device into the charger, the ...
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3answers
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Where does mass come from in pair production?

In pair production, two gamma rays with > .511Mev can come together to create a positron and an electron. So two electromagnetic waves E and B fields, with No mass and No gravity and traveling at ...
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7answers
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Quantization vs. continuous energy levels

I still don't get what it means for atomic energy levels to be continuous or quantitized (incontinuous). Clearing this up will really help me. Also, can anyone tell me why energy levels in solids are ...
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1answer
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Energy required to “glass” a given area of a temperate planet's surface

In some science fiction, orbital bombardment is portrayed as being able to vitrify the soil, or even the underlying bedrock, of a targeted area. While this is certainly not out of the question for ...
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2answers
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What determines the point of energy spillover to higher modes of a standing wave resonator?

One of the better known physics demonstrations for standing wave resonance is the singing rod . By holding the rod exactly in the middle the demonstrator constrains the first mode of excitation - the ...
3
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2answers
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How can magnetic fields have energy and yet be unable to do work with that energy? [duplicate]

Magnetic fields can't do work. However, we use the following equation to describe the energy density of a magnetic field. $u = \frac{B^2}{2\mu_0}$ The term energy density suggests that the magnetic ...
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2answers
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Conduction bands and Valence Bands, so do electrons really exist in Conduction bands?

My understanding is that conduction bands are energy bands created from the electrons in the valence shells/bands absorbing energy to jump to the next level (is this true)? Now, do the conduction ...