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.

Filter by
Sorted by
Tagged with
0 votes
0 answers
17 views

How is energy conserved in interference of light waves? [duplicate]

How is energy conserved during interference of light waves? I already know a textbook explanation that in constructive interference the resulting intensity is four times the initial intensity and for ...
user avatar
  • 338
0 votes
0 answers
24 views

Gravitational Aharonov-Bohm Effect and Conservation of Energy

Like for the electromagnetic Aharonov-Bohm effect of QED, the gravitational Aharonov-Bohm effect has recently been proven in an experiment done by Ch. Overstreet (2022), showing that the gravitational ...
user avatar
  • 738
-6 votes
1 answer
49 views

Why perpetual motion never works? [closed]

Thermodynamic laws prevent such a thing.
user avatar
17 votes
4 answers
2k views

Is it correct to say that it is theoretically impossible for perfect rigid bodies to exist?

If perfect rigid bodies were to exist, then consider a scenario in which two rigid bodies of equal masses moving with velocities of equal magnitude but opposite in direction colliding against one ...
user avatar
  • 338
1 vote
1 answer
25 views

Benefit of Hydrogen Electrolysis

I was considering building a simple solar hydrogen generator for fun and it led me to the question Does the hydrogen produced have more potential energy than the electricity used to get it? Obvious ...
user avatar
0 votes
1 answer
21 views

Transfer mechanism of two particles in laboratory coordinate [closed]

There is two particles' collision with angles theta for M1 and phi for M2. The initial velocity of M1 is V0 and of M2 is 0. The collision follows the conservation of energy and momentum. Three ...
user avatar
0 votes
2 answers
39 views

Non-Work energy conversion

Are there any conversions of energy that are not considered work, (energy change with a force and displacement)? For example heat transfer does not convert the form of energy, can something such as ...
user avatar
1 vote
1 answer
28 views

What happens to the potential energy when we connect 2 water tanks with different water levels?

Imagine combining 2 water tanks (with equal cross section areas ) with different water levels. I'll call them A( tank with the higher water level ) & B. When water is flowing from A to B, what ...
user avatar
0 votes
1 answer
50 views

To clarify the entropy/ energy/ Gibbs Eqs

Both case are isothermal and internally reversible processes. Why is it wrong to use energy conservation in case7-24 to solve the problem? I referred to the textbook (Aqueous tea An Engineering ...
user avatar
2 votes
1 answer
51 views

Energy and Momentum conservation in Bhabha scattering

I came across this question here which was asking my exact initial question (I even came from Griffiths problem 2.4 too!). But the given answer gave me a lot more questions which I think constitute ...
user avatar
  • 498
1 vote
4 answers
87 views

Why is some mass converted into energy when neutrons and protons combine to form nucleus?

So some of the mass is converted into energy when neutrons and protons combine to form nucleus. Why? And how? And then why do we need to supply the same amount of energy to separate them?
user avatar
0 votes
2 answers
73 views

What law of thermodynamics is broken here? [closed]

This question came in the Dhaka university admission exam 18-19. A heat engine in each cycle does positive work and loses energy as heat with no heat energy input. Which law of thermodynamics does the ...
user avatar
-1 votes
1 answer
72 views

Can someone explain why this would not create an infinitely rotating disk (perpetual motion) [closed]

This may be a dumb question and the solution may be super obvious but I can't figure it out as hard as I try. I have drawn a sketch of a device I thought of, now I know that we cant create "Free&...
user avatar
5 votes
3 answers
1k views

Where does all the energy in black holes go?

The temperature inside of a black hole is almost absolute zero, so particles inside a black hole have almost zero motion. So if they don't give out any heat or light, where does all the energy it ...
user avatar
0 votes
0 answers
20 views

Velocity- and time-dependent forces can not be conservative [duplicate]

I have already seen many posts about this specific question but in only a few of those mathematically rigorous answers were given. Unfortunately none of them are accessible at my level (first year ...
user avatar
0 votes
0 answers
21 views

Why is the friction in the motor wrong as an answer to wasted energy in this question?

I do not understand why the answer to part b)ii) cannot be energy lost to friction within the motor as the work done by the motor should be the total work done to move the cyclist and should include a ...
user avatar
1 vote
0 answers
36 views

Pressure wave speed $v=\sqrt{\frac{B}{\rho}}$ rearranged $\rho v^2=B$ is similar to kinetic energy: $E_k=\frac{1}{2}mv^2$. Is this a coincidence?

The speed of a Pressure wave speed is given by: $v = \sqrt{ \frac{B}{\rho}}$, which seems rearranged very similar to kinetic energy: $\rho v^2 = B$. How can this be understood, is this a coincidence? ...
user avatar
2 votes
2 answers
120 views

Free energy from the vacuum?

An electric field with an intensity of the Schwinger limit $$E=\frac{m_e^2c^3}{e\hbar} \approx 10^{18} \hbox{ V/m}$$ is strong enough to create electron-positron pairs out of the vacuum by separating ...
user avatar
1 vote
4 answers
77 views

Where does an electromagnetic wave's energy come from?

tldr; doing work on a neutron would only increase kinetic energy, but doing work on a proton would increase kinetic energy as well as emit energy in the form of EM waves. How does that work? I know ...
user avatar
  • 111
1 vote
2 answers
85 views

Conservation of energy and work done by a torque [duplicate]

Suppose you let a solid roll down an incline without slipping, from height $h$. My textbook gives the following conservation of energy relation $$mgh = \frac{1}{2}mv_{cm}^2 + \frac{1}{2}I\omega^2.$$ ...
user avatar
  • 25
0 votes
1 answer
51 views

Angular Momentum Conservation and Conservation of Energy

A heavy solid sphere is thrown on a horizontal rough surface with initial velocity $u$ without rolling. What will be its speed, when it starts pure rolling motion? So using conservation of energy, I ...
user avatar
  • 1
0 votes
2 answers
95 views

What exactly is the limiting factor of the efficiency of a heat engine?

In an imagined scenario, $n$ moles of steam at a temperature $T_h$ and pressure $p$ enter an engine. The steam leaving the engine is at a temperature $T_c$ and pressure $p$. In this scenario, the heat ...
user avatar
  • 31
0 votes
0 answers
33 views

Zel'dovich, Raizer - derive energy equation

Consider following excerpt from Zel'dovich, Raizer, Physics of Shock Waves and High Temperature Hydrodynamic Phenomena: I wonder how exactly can I derive (1.10) from (1.9)? For example, (1.9) ...
user avatar
  • 74
0 votes
1 answer
35 views

Can Energy and Momentum Conservation prevent Particle Interactions?

I understand that Quantum Numbers must be preserved during particle interactions, which prevents certain interactions from occurring. However, as Energy and Momentum must also be conserved, are there ...
user avatar
  • 329
2 votes
1 answer
132 views

How does general relativity resolve the fact that energy is not positive definite in Newtonian gravity?

In Newtonian gravity, the energy of the gravitational field $\vec{g}$ is $$ U = -\frac{1}{8\pi G}\int |\vec{g}|^{2} d^{3}x $$ (assuming we don't have any point masses that lead to singularities and ...
user avatar
0 votes
1 answer
27 views

Two final velocities for a mass launched from Earth

i'm trying to find the final velocity of a mass that is launched vertically from the earth, only considering the gravitational force. My first attempt was with angular momentum: $r$ is the distance ...
user avatar
  • 3
0 votes
0 answers
17 views

When a solid is melting how do the potential energy and kinetic energy of the particles in the solid change?

When a solid is melting, does the kinectic energy and potential energy of the particles in the solid change? Will they remain the same or increase or decrease.
user avatar
0 votes
0 answers
26 views

Deformation of gradually applied load vs impact loads?

When a load P is applied gradually on an object, the work done on it is the average of the initial and final loads, which is generally P/2 multiplied by the deflection Δ1. In the case of impact load, ...
user avatar
  • 11
0 votes
2 answers
117 views

A Tough Mechanics Problem [closed]

Here's the problem diagram: The situation is set up on a fixed frictionless horizontal table. We are required to find the time after which the block B crosses the dotted line. The diameter of the ...
user avatar
1 vote
1 answer
32 views

Will the heat generated from solar panel electricity eventually generate wind energy?

I'm curious about limits for extracting solar energy, but I never studied this stuff so I'm going to speculate a lot. My first question deals with the things like wind energy. I assume this energy is ...
user avatar
  • 11
-2 votes
0 answers
9 views

Calculation of positive energy of the universe [duplicate]

Being new to this site, I find it very difficult to navigate. I just had a question deleted for reasons I don't understand. So, I will try again. Two part question--1. How is the positive energy of ...
user avatar
18 votes
7 answers
2k views

What makes energy "the" conserved quantity associated with temporal translation symmetry?

This kind of relates to my prior question about the non-triviality of temporal translation symmetry and will use some of the same concepts: How is energy conservation & Noether's theorem a non-...
user avatar
0 votes
0 answers
35 views

Problem with work done by normal force

A block of mass $M$ with a semicircular track of radius $R$, rests on a horizontal frictionless surface. A uniform cylinder of radius $r$ and mass $m$ is released from rest at the top point A(see fig)....
user avatar
0 votes
0 answers
24 views

Total energy of the universe calculation [duplicate]

If the total energy of the universe is zero, how is the positive energy calculated--is it mass energy, kinetic energy or both? Also if dark energy is causing the universe to expand, how can the total ...
user avatar
0 votes
2 answers
69 views

Why don't perpetual motion machines with superconducting magnets work?

A superconducting magnet works by energizing a superconducting magnetic coil, then short circuiting it to make a closed loop. Would it be possible to transfer the current back and forth between two ...
user avatar
1 vote
1 answer
53 views

Are there non time-symmetric systems that increase total energy over time?

According to Noether's theorem, systems that are not time-symmetric have $\frac{\mathrm{d}E}{\mathrm{d}t}\neq0$. I have essentially two questions, then: Are there any real systems (discovered or ...
user avatar
  • 187
0 votes
1 answer
69 views

Are there any mathematically conceivable arrangements of an indeterministic universe that are not physically possible?

Are there any mathematically conceivable arrangements of this universe (particularly ones that respect its mass-energy content) that cannot in principle be achieved through its evolution in accordance ...
user avatar
3 votes
1 answer
585 views

Where is the energy going in this simple harmonic motion

Suppose i have a block of mass $M $ performing simple harmonic motion under a spring. Now suppose i gently place a particle of mass $m $ on top of it. Case 1 The mass $m$ is placed when block of mass $...
user avatar
0 votes
1 answer
14 views

Treating a rotating rod like a point mass at the cm

If I were to have a uniform rod that is rotating about one of its ends, am I able to treat the center of mass of the rod as a point mass and have the point mass rotate around the end? Image: My ...
user avatar
  • 83
1 vote
1 answer
35 views

Heating things with a lens. Theoretical limit vs. energy conservation

Recently I've heard that you can't heat up stuff beyond sun's surface temperature using sun+lens combination. It is because you can't transport heat from colder object to a hotter object. Of course, ...
user avatar
  • 2,725
3 votes
2 answers
64 views

Does it require greater force to accelerate a charged mass than an equal neutral mass?

Accelerating a charge produces radio-waves which is a form of energy. This energy has to come from somewhere. It would seem to suggest it would require greater force to move a charged mass than an ...
user avatar
1 vote
2 answers
75 views

Conservation of Energy in Different Frames

Supposed we have a spring-mass system on a train moving at a velocity $V$. The conservation of mass equation in the frame on the moving train is: $$\frac{1}{2}kx_0^2=\frac{1}{2}mv^2+\frac{1}{2}kx^2$$ ...
user avatar
  • 111
-4 votes
2 answers
65 views

Isn't the concept of light against law of conservation of energy itself?

Let's say there's a light wave travelling in vacuum, and it travels forever because it does not hit any object in its way. This light ray will produce oscillating magnetic and electric fields, but ...
user avatar
0 votes
0 answers
8 views

Can you hit a baseball further if the pitch is thrown with backspin or no spin?

Assuming you are in a vacuum and the pitch velocity is the same and the batter's swing is the same, would you hit the ball further is the pitch has 3000 rpms over if the ball has 0 rpms? I am ...
user avatar
0 votes
2 answers
69 views

Orbital Mechanics

Suppose we have an object orbiting the Earth with a circular orbit of radius $R$. We then change the velocity by an angle $\alpha$, without changing the speed. The textbook then asks what orbit will ...
user avatar
  • 101
0 votes
1 answer
76 views

Potential Energy defined for internal conservative forces

Will potential energy be always defined whenever internal conservative forces come into play? for example in case of electrostatic interaction between two charged particles potential energy is defined ...
user avatar
0 votes
1 answer
61 views

A block starts from rest at the top frictionless slide at a height $h_1$ above the ground and leaves the slide perfectly horizontally

A block starts from rest at the top of a frictionless slide at a height h1 above the ground. The block leaves the side moving perfectly horizontally at a height h2 above the ground. The block ...
user avatar
0 votes
0 answers
17 views

Where can I find data of a UV blocking glass absorption filter absorbing the visible light and re-emitting the energy as a photon of NIR?

If I understand correctly, a UV Transmitting, visible light absorbing colored glass absorption filter absorbs the visible light energy and re-emits it as near IR. On Oct 16, 2013 in How does Infrared ...
user avatar
-1 votes
2 answers
57 views

Newton's Third Law and Work Done on a Body [duplicate]

Say I push a box with a constant force $F$ causing a displacement $d$. So magnitude of work done by me on the box is $W=Fd$, and the kinetic energy gained by the box is $W$. But according to N3L, the ...
user avatar
1 vote
2 answers
49 views

Conservation of energy, incident and emitted radiation

Suppose we have an electromagnetic wave the propagates through space, in the direction of x-axis. A charged particles lies along the x-axis and at some time $t_0$ the EM wave hits the particle. The ...
user avatar
  • 261

1
2 3 4 5
59