Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
1answer
12 views

Force on Dielectric on pulling it out from capacitor

This is the text from Griffiths Electrodynamics for calculating force on dielectric on pulling it out from capacitor when the capacitor is connected to Battery so that voltage of capacitor is fixed: ...
0
votes
1answer
90 views

Energy stored in system or field?

I am having difficulty in understanding whether fields store momentum and energy or particles store them or both fields and particles store them? System of potential energy In the above source it ...
2
votes
1answer
29 views

Magnetic forces and change in the type of kinetic energy

I have been thinking about magnetic forces and how they do no work. When looking at the definition of work, it makes sense as the Magnetic forces only change the direction. My other approach to try ...
0
votes
0answers
16 views

Can you predict how much fuel you need to launch a rocket based on conservation of energy?

I was just wondering if there was a way to calculate how much fuel you need for launch, possibly to do with chemical energy to kinetic energy. Thanks
-2
votes
1answer
44 views

Another Free Energy Question :P :)

Hello StackExchange users. Before you read my question I would like to thank you for taking the time to help me out :). So anyways, my question is about the formation of coal seeming to break the laws ...
0
votes
0answers
28 views

Is the Casimir force a conservative or a non-conservative forces?

If the Casimir force is a non conservative forces, how can this affect the polarized vacuum theory in the universe's evolution?
0
votes
3answers
57 views

Work-Energy Problem: A ring pulley and mass system, in which the ring is sliding on a vertical rod [closed]

A heavy ring of mass $\;m\;$ slides on a smooth vertical rod and is attached to a light string which passes over a small smooth pulley distant $\; 'a' \;$ from the rod and has a mass $\;M(>m)\;...
0
votes
3answers
61 views

Friction converting into a heat

On my exam I had following question: bullet with mass $m$ and initial velocity $v_1$ hits wooden board of length $d$ and breaks it through. After that its velocity is $v_2$ and heat generated in a ...
0
votes
2answers
95 views

In the tunnel through the Earth thought experiment, how does total energy of a particle vary when it goes from surface of the Earth to its center?

In the typical tunnel through the center of the Earth thought experiment, a particle at the surface would oscillate between the two diametrically opposite points ignoring the rotation of the Earth. ...
0
votes
0answers
26 views

Newton law of restitution 2D

https://en.m.wikipedia.org/wiki/Coefficient_of_restitution Wikipedia States that Newton's law of restitution is valid only for one dimension collision. I understand this from the derivation, which ...
0
votes
1answer
101 views

Stuck in a mechanics problem [on hold]

The block is accelerating in horizontal direction towards right. By work energy theorem we have, $$W_P +W_G +W_N = \Delta K$$ $W_P$ is the work done by pseudo force in the frame of cylinder. The ...
1
vote
0answers
49 views

How to evaluate the period of a particle in a system with potential energy $U=-U_0/\cosh^2(\alpha x)$?

I am working through the textbook "Mechanics", from the series "Course of Theoretical Physics " by Landau and Lifshitz. In Chapter 3, where the authors talk about integrating the equation of motion $E=...
1
vote
2answers
135 views

Do calculations require energy?

A typical computer takes some energy "from the wall" while operating. I know that energy is spent on: Heating various components (psu/vrm/cpu/ram/ssd, so on) Fan/air motion to remove that heat (also ...
0
votes
1answer
58 views

Conservation of mechanical energy proof (Kleppner Kolenkow)

On page 168 of Kleppner and Kolenkow's mechanics they give a proof of the conservation of mechanical energy theorem which starts roughly as follows: The work done by a conservative force depends only ...
1
vote
0answers
28 views

How does Hawking Radiation not violate energy conservation? [duplicate]

If Hawking Radiation is produced by particle-antiparticle pairs forming from the vacuum, with one particle being absorbed by the black hole and one escaping, how is the original energy required to ...
5
votes
1answer
129 views

Will extracting power from ocean tides affect the moon's orbit in the LONG run?

Conservation of energy says that any energy extracted from our ocean's tides would have to come from somewhere. Since these tides are a gravitational effect due to the moon, it would seem that the ...
0
votes
1answer
51 views

How to calculate the conserved energy $E$ from the Lagrangian?

I am reading a PhD thesis that considers the Lagrangian $$\mathcal{L}=\partial_\mu\phi\partial^\mu\phi^\star-U(|\phi^2|)$$ where $\phi$ is a complex scalar field and $U(|\phi|^2)$ is an arbitrary ...
0
votes
2answers
26 views

Can we find the value of impulsive tension?

Suppose a ball is attached to a string of length $l$ and the string is attached to the ceiling. Now when I keep the ball close to the point of suspension and release it, it will travel a distance $l$ ...
0
votes
0answers
54 views

I don't understand how does the Conservation of Energy Law apply to a Negative Unity Power Factor?

How can this be a Law if the total watts of an electrical circuit can vary per unit of time? In other words, isn't it possible to break down this so-called inviolate Law into at least two constituent ...
1
vote
1answer
42 views

Contradiction between conservation of momentum and conservation of energy [closed]

Let's say that a $2\text{ kg}$ cart is rolling (frictionless) along a surface at $2\text{ ms}^{-1}$. A suspended $2\text{ kg}$ weight is then dropped onto it from above. If we apply the law of ...
1
vote
1answer
44 views

Deriving equation for $\theta$ [closed]

I have that the energy $E$ in a system is $$E = \frac{1}{2}L^2\dot{\theta}^2(m_1+4m_2) - Lg(m_1+2m_2)cos(\theta) + c$$ where $c\in\mathbb{R}$. I have used the conservation of energy over time to ...
2
votes
1answer
33 views

Does using a trampoline conserve energy?

In a thought experiment, we have a trampoline on the ground (well it's fancier than a spring) and a ball which is made to undergo free-fall from a height $h$. In a non ideal scenario, will the ball ...
1
vote
2answers
63 views

Conservation of energy when slowing an object down

If it takes energy to slow an object down, and then the object also loses KE, then how is energy conserved? Don't you have a net loss of energy?
-1
votes
1answer
49 views

How do conservative forces conserve mechanical energy?

A force that conserves mechanical energy is known as a conservative force. Question: How do conservative forces conserve mechanical energy?
1
vote
3answers
76 views

$\Delta K=\Delta U$ vs $\Delta K = -\Delta U$

While doing physics homework, I noticed that in some problems, the change in kinetic energy(KE) is equal to the change in potential energy(PE), even though I learned that conservation of energy shows ...
1
vote
1answer
59 views

Oscillation of 2 identical pendulums connected by a rubber band

While solving A level past papers, I came across the following question. For reference, this is the Edexcel GCE A2 Physics Paper 2 from June 2018. What does not make sense in my mind is the fact that ...
0
votes
1answer
49 views

Is the total mechanical energy conserved in a system that's a simplifying approximation of an actual roller coaster?

Suppose you have a 2-dimensional Euclidean space where one dimension goes left and right and the other dimension goes up and down where one of the units of length is the meter. Furthermore, suppose ...
1
vote
1answer
36 views

Magnetic Field Energy Increase while magnetic field does work on a current carrying loop - Where does the energy come from?

Imagine you have an external magnetic Field $\vec{B}_{\text{ext}}$(for the sake of simplicity, it should be constant throughout the entire space), which is not generated by any current density (...
1
vote
1answer
14 views

Energy conservation in induced emf in open loop

We have a closed loop in the influence of magnetic fields of electromagnets somewhat like this. (Kindly ignore the currents and forces shown - the coil is stationary and initially no current flows) ...
0
votes
1answer
34 views

The work due to friction given an influential force

Statement: I am trying to work through Chapter 8, Problem #70 of OpenStax University Physics Volume 1 and I cannot figure out what I'm doing wrong. The problem statement is as follows: A particle of ...
0
votes
3answers
55 views

Are 40 Kelvin interstellar gas clouds evidence of virtual positron and real electron annihilation

Given that Hawking radiation includes separation of a virtual electron-positron pair, then why cannot it be the case that in the vicinity of a real electron it annihilates with the virtual positron? ...
-1
votes
1answer
32 views

Energy convertion

Why cannot light energy and sound energy be interchanged? Why is energy converted always in kinetic? Why cannot potential energy be converted from one form to the other when energy is in mechanical ...
0
votes
1answer
20 views

Work done and change in mechanical energy

I have a hard time understanding the equation $W_{Driving} +W_{Friction} = \Delta E_{mechanical}$ Is there any derivation of it?
2
votes
0answers
37 views

Does gravity follow law of conservation of energy? [duplicate]

Law of conservation of energy states that energy cant be created nor destroyed.I dont understand how it is applicable for a object moving under influence of gravity.If some force has been applied on ...
0
votes
2answers
52 views

Is the energy of an electromagnetic wave, in electron volts, an 'average' or a 'peak' value?

Since EM waves oscillate, is the energy given in eV an average or maximum value? In a related question, can a detector (of whatever sort) 'miss' an EM wave if the amplitude is at a minimum when it ...
0
votes
1answer
27 views

Discrete energy rounding

If energy is only found in discrete amounts what happens when the amount of energy falls below the minimum individual unit? does it have a floor or ceiling function or does it matter what type it is?
-1
votes
1answer
40 views

Is there violation of energy conservation when a particle transforms to its anti-particle, for example $B^0\to\bar{B}^0$, or $K^0\to\bar{K}^0$

additive information : $B^0$ and $\bar{B}^0$ don't have the same mass, $K^0$ and $\bar{K}^0$ don't have the same mass. is there energy violation? if yes, is the key explanation of this coming from the ...
0
votes
0answers
59 views

Are there any real ways at least in theory to manipulate quantum vacuum for propulsion or energy generation? [duplicate]

https://patents.google.com/patent/US10144532B2/en US Navy was granted a patent for polarised vacuum propulsion using microwave radiation and high em energy resonating cavities. It seems to be a ...
0
votes
3answers
97 views

Work and energy - explanation of definition [duplicate]

I have a question about the definition of energy. the definition is "ability to do work". what does it mean? what is the ability that the definition talks about? what is the meaning of ability in ...
21
votes
3answers
3k views

When an electron around an atom drops to a lower state, is 100% of the energy converted to a photon?

Let's say we have an electron around atom. Let's say the electron drops into a lower electron shell. Is 100% of the energy difference converted to a photon? Does the atom recoil at all? Is the any of ...
1
vote
1answer
47 views

Atomic model - absorption [duplicate]

I have a question regarding the absorption of light in e.g. hydrogen atoms: I didn't quite understand how the electron knows that it can only absorb photons of the right energy. I thought that when ...
0
votes
0answers
16 views

Frictional losses in flexible tubing with multiple branches opening up to a large tank

I am working on designing an experiment where I will be creating a wall-jet flow where the wall is a rotating wing. After some thought I realized I need to estimate the pressure losses due to the pipe ...
0
votes
0answers
26 views

Determining Whether a Given Hamiltonian is Conserved

in simple terms I'm looking to understand how we can tell whether a given Hamiltonian (or one that we've deduced) is conserved or not? I've tried looking at other similar questions but am not sure I ...
0
votes
1answer
82 views

Not able to clearly understand the text of a problem [closed]

I've not clearly understood what it's meant by the text of this problem. To me, it seems that I have to show why an object travels AB in less time than ACB. However, if an object travels from A to C, ...
0
votes
2answers
32 views

Find the resultant force in a motion problem with a loop

In the approximate diagram, the block with mass $m$ starts without movement in the position $P$ in the top of a hill with height $5R$. After that, the block falls down through the hill, and reaches a ...
-1
votes
6answers
63 views

How is speed affected (or not affected) by acceleration by gravity?

I am a new physics student and I was reading a question posted on here earlier: Which Sphere is Fastest? It posits that three spheres thrown with the same speed at the same point (one thrown ...
12
votes
3answers
1k views

Which sphere is fastest? [closed]

I was doing a physics problem, and it seemed simple at first, but now it doesn't at all, and I need help. Here it is. Three identical spheres are thrown from the same height above the ground. Sphere ...
2
votes
2answers
56 views

What if we set the exact equality $u^2=\frac{2GM}{R}$? Escape or not?

Let an object of mass $m$ is thrown up with an initial velocity $u$ from a spherical gravitating body $A$ of mass $M$ and radius $R$. Let us assume that when it reaches a height $h$ its velocity ...
0
votes
1answer
18 views

Why does setting kinetic energy equal not work in inelastic collision?

From my understanding, in an inelastic collision there is no loss of kinetic energy. So if we take the following problem: A 7700kg car is traveling 18 m/s and strikes a second car. The two stick ...
0
votes
1answer
66 views

$E = mc^2$ and Binding Energy Confusion [closed]

I have been introduced to $E =mc^2$ and binding energy recently while studying nuclear physics and I have a hard time understanding the following: Mass-Energy what does $E=mc^2$ really mean, as I ...