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 in the Relativistic COM Frame

I have been taught that in Classical Mechanics, the total energy of a system of two particles in the Centre of Mass Frame is given by $$ E_\mathrm{total} = \frac{1}{2}MV^2 + \frac{1}{2}\mu v_r^2 $$ ...
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3answers
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General relativity without energy?

I am kind of new to GR but I have been familiar with the concepts for a long time, I am getting used to the mathematics just now. My question is, what would GR predict if we would have an empty ...
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25 views

Minimal possible energy to make calculation [duplicate]

Are there any restrictions to energy that must be consumed to make calculations? Can calculations theoretically be done without consuming it?
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How much energy will fall into the eye given luminosity of display

The smart-glasses have tiny display. The manufacturer says the display has luminosity of $2000 cd/m^2$. The area of display is around $0.0002 m^2$. The reference smartphone display has luminosity of ...
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1answer
51 views

The only Energy is Kinetic Energy, isn't it? [closed]

I'm really looking for a discussion on this and don't really have a specific question. But this seems to be the best forum for such a topic. I could try to phrase this in a question, but I think that ...
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1answer
142 views

conversion of units

I have a quantity that I need to convert to different units. First, I need to note that the value is in the natural units system. The quantity is in cm^-1 (or, to be accurate, $cm^{-1}\hbar c /k$, ...
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0answers
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How to solve this energy problem using trends related to impulse and momentum? [closed]

The question runs a 1kg block moves with a speed of 10 m/s. It strikes a spring that has a spring constant of 25 N/m. Determine the maximum compression of spring. The energy way of solving ...
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1answer
14 views

How is the kinetic energy of an object in collision converted to work done in deforming itself?

Usually, in a perfectly inelastic collision, maximum amount of KE is lost. I guess it depends on the rigidity of that object collision if any KE at all will be converted to work done to deform. ...
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Why does carbon help with electron transfer in a dye sensitized solar cell?

what property of carbon(soot) makes it easier for electron transfer within a dye sensitized solar cell?
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1answer
79 views

What's Wrong With This Quantum Analogy?

"Sometimes the idea of the quantum is compared to the units we use for money. A dollar can be divided into smaller units, where the cent is the smallest possible unit." A question I came ...
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1answer
34 views

Is average kinetic energy equal to the total thermal energy of a gas?

"Average KE" as in this equation: $$K_{average} = \frac{3}{2} kT$$ Since potential energy in ideal gas model is eliminated, I guess this equation is also for the total thermal energy of a gas/a ...
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1answer
84 views

Why we can't define energy in accelerating frame?

In my old unanswered question about accelerating frame, I have found (later after editing that question), that one of the keys is that energy is not defined in accelerating frame. What I do not ...
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0answers
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What is the most energy efficient way to run an A/C unit?

I recently installed a 12,000 BTU Mini-Split A/C unit with an inverter - http://www.tempstar.com/products/dfac.html I was told that it uses approximately 0.6Kw/hour. What I am really curious about ...
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2answers
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The correspondence of potential energy with reality

I'm a bit in doubt about whether the concept of potential energy has any correspondence to the real world. Real world entities can't change their magnitude in an instant, nor without being affected ...
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3answers
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How is Work by a System Interpretated in the First Law?

Good evening. I've happened to be sitting down today and just couldn't wrap my head around this question which seems rather simple at first. From reading about the first law and sign conventions as it ...
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1answer
71 views

Is there a formula/relationship between $q$, $m$, $c$, $\Delta T$ and $t$ (time)?

I am currently doing an experiment where I am burning methanol to test for the heat of combustion. To test this, I am heating 100g of water and raising it by 20 degrees Celsius before extinguishing ...
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2answers
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How much energy is released per unit mass from depressurizing degenerate matter?

A neutron star remnant consists mostly of neutron degenerate matter. If you happened to suddenly have 1 kg of it in your lap without the pressure necessary to keep it degenerate, I suppose it would ...
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2answers
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How is finite energy spread wholly in the infinite universe

We all know that energy is never lost, but it transforms into another form. Doesn't that mean that energy is not unlimited? I mean, why is it that way if it was infinite? However, if energy is spread ...
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1answer
49 views

Is Dark Energy and or Dark Matter directly proportional to EMR? [closed]

Is Dark Energy directly proportional to Electromagnetic radiation (EM radiation or EMR)?
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Black holes – Irrotational vortex or Rigid-body-like vortex

As light enters a Black hole – does the light enter as “Irrotational vortex” or as “Rigid-body-like vortex”? https://en.wikipedia.org/wiki/Vorticity Thank You
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2answers
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seperate engines working vs single engine

What is more fuel efficient: Two identical cars running at 50mph or one being tied to the other and only the first dragging both at 50mph? Or what requires less fuel: Two cars to start from stop and ...
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0answers
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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
76 views

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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36 views

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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1answer
40 views

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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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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1answer
73 views

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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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
52 views

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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4answers
152 views

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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1answer
83 views

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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1answer
33 views

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
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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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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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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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1answer
33 views

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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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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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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2answers
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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 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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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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1answer
24 views

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
74 views

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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0answers
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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
33 views

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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1answer
42 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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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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3answers
127 views

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 ...