The law of conservation of energy, which states that the amount of energy in a system is constant. For questions about Earth's environment, see the climate-science tag instead.

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Finding the angular velocity of a rod hit at a distance from its pivot [closed]

A 1m long, 2kg stick is nailed to the wall with a single nail, allowing it to pivot and freely rotate at the end. A 1kg ball, with speed 3m/s makes contact with the stick at some distance x (unknown) ...
3
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0answers
215 views

Why 'Force x displacement', and not momentum to measure energy? [closed]

[I have changed the title and also edited the question in other ways to make it clearer what I am asking. I hope it no more reads like a duplicate. Nor it remains any more a history question.] I have ...
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1answer
407 views

Falling rope problem (disagreement with solution found at Problem Set)

On a frictionless table there is a homogeneous rope of length $L$ and mass. We push the rope such that it immediately starts falling due to gravity. Find the velocity when the rope has fallen of the ...
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0answers
63 views

Rest masses, binding energy - mechanism for negative mass

Let us have an two objects (in a box) both of mass $m_0$ far from each other. They attract each other and at some moment their distance is close and they have substantial kinetic energy. Something ...
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1answer
59 views

Paradox of wave energy

Imagine that a wave with energy $E$ is given. as we know $E$ is relevant to the $A^2$($A$ is amplitude) now consider another wave (as same as the first one) and these two wave having a constructive ...
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1answer
332 views

Why don't virtual particles violate conservation of mass/energy?

If virtual particles sometimes add more mass/energy to a system then was inputed or comes out in the output, how do they not violate conservation of mass/energy.
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1answer
108 views

Do we need Escape Velocity [duplicate]

This may seem silly a lot but I really need some clarification on the necessity of escape velocity for a rocket leaving the Earth's gravity. A stone thrown vertically upwards reaches to a certain ...
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1answer
87 views

Bounce height of ball on Mars vs Earth

I understand that if a ball is dropped on mars and on earth the ball will bounce back to basically the same height on both planets thanks to the law of conservation of energy. But can anyone prove ...
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1answer
270 views

Conservation of Energy in Double Slit Experiment

How is energy conserved In Young's Double Slit Experiment ? In destructive interference , energy is lost . So what happens to that lost energy ? Does it escape as heat ?
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1answer
57 views

A central force which enables a torque on a sphere - is it still conservative?

Consider the following example: Two spheres (one big, other small) standing vertically on ground. At first, the small sphere is on top of the big sphere. Then, it starts to roll w/o slipping to ...
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4answers
141 views

Is energy of a quantum mechanical moving particle conserved?

From the Schroedinger equation $$ H\psi=E\psi, $$ if we want to measure the total energy of a quantum mechanical moving particle, then we have to apply the Hamiltonian operator to the wave function ...
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1answer
204 views

Understanding the relationship between electric energy and force

I'm trying to do the following problem: One of the three types of radioactive decay is "β decay", during which protons decay into neutrons or vice­versa, emitting either electrons (β­) or positrons (...
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3answers
335 views

Is the accelerated expansion of the universe consistent with conservation of energy? [duplicate]

If energy can neither be created nor destroyed, how come the universe is expanding at an accelerating rate? Where does this energy come from?
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2answers
500 views

Negative energy of universe

According to a little I have understood whatever we see in the universe is its postive energy and there is so an equal negative energy. Is this Negative energy the Dark energy? which is responsible ...
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3answers
418 views

Does energy conservation not hold in fission and fusion processes?

I have read that during fission and fusion processes, there is some kind of equilibrium between the single nucleus and the disintegration products, so they are constantly being converted into each ...
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1answer
24 views

Determining a velocity value using energy conservation

The idea is to create an experiment that'll give you the initial velocity value with which you throw a ball down at 1 meter so it bounces to 2 meters. I don't have a solid Coefficient of Restitution ...
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2answers
120 views

What observations would be needed to falsify the law of conservation of energy? [duplicate]

I've been doing some thinking, and began to wonder: What observations have led us to the conclusion that ‘energy can neither be created nor destroyed’? Essentially, this means that the big bang ...
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3answers
505 views

If a body is at rest at Earth's surface, can we say that its kinetic and potential energy are $0$ simultaneously?

If a body is at rest at Earth's surface, can we say that its kinetic energy $E_{\textrm{kin}}=0$, and its potential energy $E_{\textrm{pot}}=0$ also? Because its velocity $v$ and height above ground $...
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2answers
68 views

Do transferring energy and applying force to a body imply same?

Do transferring energy and applying force to a body imply same meaning? When we say, "I throw a ball using my pushing force so on the other hand, can I say that I transferred my kinetic energy to the ...
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1answer
57 views

Energy conservation if photon absorbed below resonance

Suppose I have some quantum system (like atom) with excitation energy $E_{exc}$ which is homogeneously broadened due to finite lifetime. I shine light with narrow spectrum centred around energy $\...
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1answer
93 views

Determine the value of $g$ with rolling ball

At first, I thought the value of $g$ ($9.8m/s^2$) could be determined simply by placing a ball at the top of a ramp at a known height. The ball was released with no initial velocity, and the final ...
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1answer
109 views

Is information a form of energy? [closed]

To better describe my question, do the following experiment: Calculate x=12+26+67+71 Now you might have spent some time in getting the answer. You burnt sugar, you used up energy to get the ...
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2answers
93 views

Energy drain in damped oscillator

Suppose we have a mass on a spring with a damping term. The equation of motion is given by: $$m \ddot{x} = -kx - c\dot{x}$$ I believe solutions are damped oscillations of the form: $$x = x_0 e^{-\...
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4answers
146 views

Conservation of energy, and Newtonian physics that does not fit

Here is a theoretical example where the energy into the system does not mach the energy output. There is no friction or air resistance. A sledge with a rocket engine attached to it is lying still on ...
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1answer
90 views

How can a moving frame transmit energy (a fighter plane shoots a bullet)? [duplicate]

This question shows that a bullet shot from a flying plane receives a large amount of energy from the plane, even much more than the energy from the propellant of the bullet. But I wonder how can the ...
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2answers
118 views

Conservation and forces/energy

Are there really non-conservative forces in actuality ? Feynman states in his book that in fact, all forces are conservative ( originating from conservative vector-fields ), provide we look close ...
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2answers
256 views

Does a mass falling towards the earth obey conservation of energy?

I'm trying to grasp basic concepts of energy and I have a question regarding conservation of energy. According to Feynman's book and Wikipedia, the law of conservation of energy states that ...
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1answer
184 views

Is it, and if so, why, impossible to build perpetual motion machines (PMMs) in GR?

I am wondering about this. I have heard that in General Relativity (GR), the energy in a space-time may not be well-defined. If that is the case, then it would seem "conservation of energy" would not ...
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1answer
84 views

Wondering about Energy [duplicate]

Me and Energy I'm trying to move along with my study of non-advanced physics but not grasping what energy really is, is driving me nuts. Whenever i see anything about energy ( Kinetic, Potential,...
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1answer
58 views

Ballistic pendulum - are all forces conservative for this case?

For the Ballistic pendulum in the image below: Are we allowed to assume that after the bullet hit the log (mass M), then there's a conservation of energy? (Thus $\frac{1}{2}(M+m)V^2 = (M+m)gh$) ...
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4answers
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What is the energy of a superposition of energy eigenstates?

$\newcommand{\ket}[1]{\lvert #1 \rangle}$Suppose I have a system say SHO in a superposition of energy eigen states $\ket{n_1}$ and $\ket{n_2} $ given by $\ket{\psi} = \frac{1}{\sqrt{2}}\ket{n_1} + \...
2
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1answer
192 views

“Where” does dissipated enstrophy go?

We are all familiar with the kinetic energy dissipation and how it is converted into heat which can either be radiated away or go into the internal energy of the system. In the enstrophy transport ...
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3answers
85 views

Work power and energy

When you push your bicycle up on an inclined the potential energy of the bicycle and yourself increases. Where does this energy come from?
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1answer
141 views

Relationship between energy density and energy flux

I'm presently working on obtaining conservation laws via symmetries. These conservation laws are written as 2-element vectors where each element is the energy density and energy flux. To proceed in my ...
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4answers
315 views

What starts the conversion between GPE and KE?

When researching GPE and KE conversion, lots of websites say that as an object with GPE (Gravitational Potential Energy) falls, that GPE is converted into KE (Kinetic Energy), so there is less GPE and ...
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6answers
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Can orbital energy be a source of perpetual power?

A thought just came to me, and I want to comfirm it here: If we figured out a way to harvest the energy from the orbit of the Moon, would that be perpetual? The Moon has been orbiting the earth for ...
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5answers
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How gently could a comet/asteroid/meteorite “hit” Earth?

Could an object from outer-space with the right velocity and orbit come into contact with the surface of our planet in a manner that wouldn't cause it to burn in our atmosphere?
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1answer
160 views

Falling charged objects: energy conservation paradox?

Imagine that we start with two oppositely charged objects on the ground, separated by a distance $d$, with charges $+q$, $-q$ and masses $m$. We raise them both up to a height $h$. In doing so we ...
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1answer
83 views

Apparent Violation of Energy Conservation in an Electromagnetic system

As shown in the figure a beam of EMW pulse is propagating towards a nearly point charge.Here if we calculate the total energy of the system by the equation mentioned in photo - we get that the total ...
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3answers
107 views

What happens to KE when lowering a raised book?

I understand the conservation of energy theorem and mechanical energy, but there is this question that confused me a bit, so I hope someone explains it. If you had a book and you raised it, you gave ...
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70 views

Brownian Ratchet Plausibility

Alright I'm going to throw whatever reputation I have on the line here. And yes this is a serious question. Apologies for the shoddy imagery. I had a couple ideas to get the Brownian Ratchet to ...
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1answer
80 views

Where does energy goes if I jump down from a balloon?

Suppose you are in a hot air balloon of mass $M$ which is floating in the air, and you get out and start climbing down a rope at constant velocity $v$. By conservation of momentum we can show that the ...
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1answer
115 views

Where does energy goes when I work out?

Let's say I am using a machine to lift weight by pulling a bar. When I do that, the state of the machine is exactly the same at the beginning and the end of the workout; no heat has been generated ...
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1answer
191 views

What specifically is incorrect about the Dirac Sea interpretation?

So taking the square root of $E^2 = (m_oc^2)^2 + p^2c^2$ yields two solutions. The Dirac Sea treats the negative solution as an infinite space of electrons with negative energy. All the observable ...
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4answers
259 views

Why does this ball have potential energy at its lowest point?

A ball of radius $r_0$ starts from rest at point $A$ on the inside of a track of radius $R_0$. The question is what will its speed be when it reaches the lowest point of the track, point $B$, assuming ...
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1answer
132 views

What are the necessary/sufficient conditions for a system to be Hamiltonian/non-Hamiltonian?

I searched for a definition of Hamiltonian system on Huang and Tuckerman text but have not found anything precise. So intuitively I suppose: Hamiltonian system= a system which admits a complete ...
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1answer
8k views

What happens to kinetic energy of an object when i stop its motion? [duplicate]

Assume an object is moving and it is stopped at a point . Now kinetic energy will transform into some other energy . what can be those energies and on which cases these will happen respectively ? ...
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2answers
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If an object falls - regarding air resistance - does the Potential or Kinetic energy get converted into thermal energy as it is falling?

I read a paragraph on the transfer of potential energy to kinetic energy and heat from this website: Even if air resistance slows down the ball, the potential energy is the same (Mb x g x H). ...
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1answer
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How is energy conserved in a series of magnets, progressively moving another magnet upwards?

Imagine a tall building with windows allinged one above the other, and a railway going from the bottom of the building to the top of the building (vertically), right where the windows are. Imagine ...
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2answers
151 views

Gravity and its energy

Where does gravity get its energy from? So, I'm taking a high school environmental science class and we just started a unit on energy. We were talking about different types of energy and one was ...