# Questions tagged [energy-conservation]

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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### Does a rocket moving in a circle expel exhaust at a greater velocity?

Consider a rocket undergoing constant acceleration in a rectilinear path. Assuming the rocket is ideal (ignoring fuel mass and energy loss such as sound, radiation, vibration, etc.) a portion of the ...
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### Why in two block system, both block tends to have same velocity at maximum potential energy when no external force is applied? [closed]

Consider a hemispherical bowl and a block placed inside it if the bowl is given velocity $v$ and given that there is no friction, the block will gain kinetic energy and then will rise to a maximum ...
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### Energy Transfer and Work in Action-Reaction Forces [closed]

simple but confusing for me. I hope this question doesn't close or disappear. Questions continue to arise about work and energy. Situation Description A and B exert forces on each other and do work. ...
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### Is it possible to lower the energy of the vacuum?

The energy of the vacuum is given by $$\sum_k \frac{1}{2}\hbar\omega_k.$$ However the frequency $\omega_k$ depends on the wavevector $k$ and some constants like the speed of light $c$, which in turn ...
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### Is it possible there can be a non-Fourier model of string vibration? Is there an exact solution?

I am looking for a model of string vibration that does not assume the string is Fourier. Is there a Hamiltonian? The equation of motion must be a function of length and tension, not time, and it must ...
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### Do off-centre forces create additional energy?

When a force is applied to a rigid body at its centre of mass, it accelerates. Over time, that acceleration becomes velocity, which gives the body a certain amount of kinetic energy. However, if that ...
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### The $\alpha$ particle's energy inside a nucleus is lesser than the Coulomb barrier height. Justify

The $\alpha$-decay is usually explained via quantum tunnelling. This is because the $\alpha$ particles do not have sufficient energy to climb over the Coulomb barrier. But how do we know this? We can ...
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### How can a free electron and an ion in a plasma recombine without violating conservation of energy and momentum?

This question is the inverse of How does ionization of gas molecule affect the translational kinetic energy of the molecule? The answer to that question is that a molecule cannot spontaneously ionize: ...
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### Modified Joule-Thomson expansion

I was trying to solve a thermodynamics problem about the Joule-Thomson (Joule-Kelvin) expansion and I can't reach the answer. The book has the solution, but there's a term which I don't get where it ...
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### Do all nonlinear systems store energy?

I would like to clarify, this question comes from my own curiosity while solving for nonlinear differential equations. I have noticed that I lack the fundamental understanding of linearity/...
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### Does a block's velocity becomes zero when it hits a spring?

It says the velocity of the block becomes zero at the instant of maximum compression. But does it not go with a constant velocity as it's a smooth part? It should hit the spring and then oscillate for ...
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### Energy and momentum conservation for light reflection [duplicate]

There is a radiation pressure which means that when light reflects from a surface, the surface will get some momentum/energy. If so, what is the balancing change on the light/radiation side if light ...
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### Are calories an appropriate measurement of energy for biological systems? [closed]

According to this source, a calorie is an inappropriate unit to quantify the energy contained in food because a "calorie is heat energy" and "humans don't absorb photons" but ...
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### When are two object guaranteed to keep getting further and further away?

In a two-body problem, it is known (if I understand correctly) that if the specific orbital energy of the system is $\varepsilon \geq0$, then the objects must eventually escape each other. My question ...
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### Is it impossible to construct a Faraday cage that can block a *static* electric field?

I think the answer is yes. My reasoning is this: Imagine for argument's sake, we could have a charged negative source that has its field blocked by a Faraday cage. We can transport a positive charge ...
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### Why does my potential energy decrease when lifting a book?

I was reading morin's intro to mechanics book, and i reached the point where he was discussing work potential energy equivalence, which i find very confusing right now... basically we are analysing me ...
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### How do I calculate change in flux in an augmented rail accelerator without violating conservation of energy?

Suppose I have two rails and a wire connecting them I'd like to accelerate. Then $\frac{d\phi}{dt}=Bvl$, where $B$ is the magnetic field strength where the wire is, $v$ is the velocity, and $l$ is the ...
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### Suppose a shell of a sphere formed by matter and with large radius, start afterwards to diminish the radius, give $E=mc^2$ the system stops

Thinking in classical mechanics terms but with the knowledge that $E=mc^2$ let's make the below thought: Suppose you have a shell of a sphere formed by a mass uniformly distributed over the surface of ...
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### Does all electrical energy in circuits convert to heat?

Electric power is defined as "the rate of transfer of electrical energy within a circuit" as per wiki. Its formula is given as $P=VI$. But then heat dissipated by current in a circuit is ...
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### Energy created by gravity

So just a thought experiment: I take my rocket and fly through space. Meanwhile I pick up some piece of debris that experiences no (big) gravitational pull. I attach it with an infinitely long rope to ...
1 vote
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### Are there structures or systems that can have a high angular momentun that are not made by protons and/or neutrons?

Cosmic structures such as neutron stars, white dwarfs or black holes can have high amounts of angular momentum (high spin velocities). However, these are all made by protons and neutrons (black holes ...
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### How do I associate signs with energies when using the law of conservation of energy?

When I was studying vertical spring systems, I came across this question: A spring that has a 1.25 kg mass at one end is attached to a fixed support and left to oscillate freely. When oscillating, the ...
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### Is energy conserved on a ball sliding without friction?

If a ball is sliding without friction (down an inclined surface) is energy conserved? I can’t think of why it wouldn’t be, but my intuition on this stuff is really bad.
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### How can maximum kinetic energy not equal to total energy in SHM$?$ [closed]

A linear harmonic oscillator of force constant $2×10^6$$\,\text{N}\,\text{m}^{-1}$ and amplitude $0.01 \,\text{m}$ has a total mechanical energy of $160 \,\text{J}$. Find ratio of maximum potential ...
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### Why do objects roll down slopes at the same speed?

I had to do an online simulation in class, and for some reason an object with twice as much as another rolled down a slope at the same speed of the other object. In other words, objects with a large ...
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### Noether's Theorem in relativistic cosmologies [duplicate]

Is Noether's Theorem valid within the context of relativistic cosmology? If not, does this mean that the universe does not conserve energy on cosmological time and distance scales?
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