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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7
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1answer
64 views

Why does paper explode when compressed?

Various videos online show paper/card suddenly releasing energy in an explosion like way and transforming into a brittle material when put under sufficient pressure from presses. Examples are shown ...
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2answers
39 views

What is more basic thing to explain phenomenons : Energy or Force?

You know many physical happening are explained by considering forces or we can explain these phenomenon using energy (like energy conservation, etc.). so i was wondering that explaining the physical ...
7
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1answer
260 views

What happened to this folded paper in a hydraulic press?

The video below apparently shows a man folding an A3 size piece of paper 7 times, putting it under the hydraulic press each time. After 7 folds, on the last press, the paper sort of explodes. What's ...
2
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1answer
23 views

Does a degassed magnet weigh less than one that is not?

I learned matter with an electric current weighs more than matter with no current. Does that apply to magnetic material in the same way but with it's magnetic fields instead of electric current? A ...
0
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1answer
31 views

Energy Transferred to a Spring by a Time Dependent Force (using Fourier Transformations)

I found an excersice in Byron-Fuller's: "Mathematics of Classical and Quantum Physics", about the energy which is transferred to a spring by a time depended force of the form: $F(t)=\left\{ ...
1
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1answer
26 views

Wind turbine impact on cars fuel consumption [on hold]

I have question that I still can't resolve. How much cars fuel consumption rises(l/100km) if I attach 1 kW wind generator to cars body? How can I calculate that and what do I need to know? ...
1
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1answer
38 views

Why does time-independent Hamiltonian not depend on angle variable?

In Landau and Lifshitz Mechanics, $\S50$ Canonical variables a time-independent Hamiltonian is considered, and a canonical transformation is done such that adiabatic invariant $I$ becomes the new ...
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2answers
59 views

Work done according to Newton's Principia

Actually I was going through the principia, reading Newton's derivations of the properties of ellipses. Suddenly I had this question which got stuck in my mind - Throughout Principia Newton uses the ...
1
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1answer
142 views

Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
0
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1answer
27 views

Can potential energy exist in the absence of gravity?

Can other forms of potential energy exist that use forces besides gravity, such as magnetism, or simply the pull provided by a moving body to which the object whose potential energy is being measured ...
12
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3answers
1k views

Energy needed for Superman to take off and fly at the speed of sound

I just watched "Man of Steel", and I'm wondering if my logic is correct. Let's assume Superman is 80 kg. The energy required to take off from the rest to reach the speed of sound in air (if I neglect ...
3
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1answer
43 views

How to calculate number of degenerate states?

For example if we need to get number of degenerate states for a particle confined in a 3D box that have energy $$E=41\frac{\pi ^2 \bar{h}^2}{2m_e L^2}$$ I know that $$E=\frac{n^2 \pi ^2 \bar{h}^2}{2 ...
0
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1answer
36 views

Energy required to accelerate from different reference frames

So I've recently been studying relativity a lot trying to understand it and I feel like I grasp most things conceptually but I have one issue I've been trying to understand for the last couple days ...
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1answer
47 views

Which one of these energy formulas is correct? [on hold]

Which one of the following formulas is correct? What do they mean/represent? How are they used? $E=mc^2$ $E^2=m^2c^4+p^2c^2$ $E=\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$
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1answer
55 views

Why can´t we call the energy released after the annihilation of a particle and its antiparticle `pure` energy? [on hold]

As a particle and its antiparticle annihilate each other a huge amount of energy is released, and no mass is left. This energy always comes in the form of force mediating particles (photons, gluons). ...
3
votes
2answers
257 views

The ADM Energy of Gravitational Waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of Gravitational Waves.And they said the result ...
-3
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0answers
47 views

A Take on Dark Energy [on hold]

Extreme over-simplification alert (the full proof is hundreds of pages long and it’s quite unfinished as of yet). Okay, I have a simple (enough) explanation of what dark energy is, but I am not sure ...
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2answers
62 views

Model/formula for bouncing ball

I'm programming an animation of a bouncing ball, and I want it to be as realistic as possible. I fully understand the physics while the ball is rising and falling: It accelerates downward at 9.8 ...
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0answers
39 views

Homework guidance [migrated]

I don't know where else to place this comment because I think I deleted my earlier question. This afternoon I asked a question about whether or not it was feasible for a gust of wind to alter the ...
0
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0answers
28 views

Temperature of a single dipole [duplicate]

When taught about the temperature of a system from an illustrative point of view, I was told to think of molecules vibrating and hitting one another. If the molecules vibrate faster and faster (and in ...
10
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3answers
158 views

Are mechanical energy of an element of a rope and energy density constant in the case of mechanical waves?

I'm confused about energy driven by a wave. Consider a sinousoidal wave moving in a rope. In my view each element $dm$ of the rope follows a simple harmonic motion in time. That means that the ...
0
votes
1answer
47 views

Double Integrals of Force

I took AP Physics C and Multivariable Calculus last year, and noticed something interesting. For non-relativistic particles in one dimension:$$F=\frac{\partial p}{\partial t}=\frac{\partial ...
-5
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0answers
44 views

What gives a mass the ability to do work? [closed]

What gives a mass on the fundamental level the ability to do work? If you push an electrically charged mass against a mass with is charged with much more electricity (of the same charge) how is the ...
2
votes
1answer
102 views

Confusion in understanding of quantum fluctuations and vacuum energy

I'm having a bit of trouble understanding what exactly is meant by a quantum fluctuation of a quantum field and its relation to the vacuum energy attributed to such a field. Is the point, that due ...
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1answer
33 views

Do we mean with 'pure energy' the force-carrying particles? [closed]

I often read, hear and talk about pure energy. What is meant by this? Does pure energy consists of the forces between matter, or the force mediating particles, like the massless photons and gluon? I ...
34
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4answers
17k views

Why can't energy be created or destroyed?

My physics instructor told the class, when lecturing about energy, that it can't be created or destroyed. Why is that? Is there a theory or scientific evidence that proves his statement true or ...
1
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1answer
135 views

Do solids have translational energy?

Along with having vibrational energy, do both crystalline and amorphous solids also have translational energy? I ask because I've always understood solids to have just vibrational motion/energy. But ...
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0answers
30 views

Calculating mechanical motion/velocity of a pendulum/swing? [closed]

I am a bit new to this so sorry if I mess anything up. Just needed some help with this question. A mom puts her 20kg son into a swing seat and pulls him back so he is 3.00m vertically to the lowest ...
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0answers
12 views

How much heat can ULF RF waves can generate? [closed]

How much heat can ULF RF waves can generate? Can the heat generated from RF waves burn of insects wings which are in flying state?
3
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2answers
1k views

Energon: is it possible?

I'm always quite curious about the "Energy cube" in Transformers, or namely Energon. Is it really possible to store energy, such as electricity, into such a compact form? safe to distribution, and ...
3
votes
2answers
63 views

Blocks releasing heat energy [closed]

If you had two blocks, two different sizes yet the same temperature. Which one would release the most energy in the shortest amount of time and why?
2
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4answers
527 views

Why does light bend?

I have just read about dispersion of light by a prism and the thing which i donnot understand is that WHY does the light bend at all? Through prisms and slabs? I came to know that red light has the ...
0
votes
1answer
19 views

Difference between energy loss at high voltage and high current

When reading about power transmission one very common statement is that power is transmitted at high voltage to minimize loss in the form of heat. What confuses me is the governing equation. Aren't ...
2
votes
2answers
52 views

Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
0
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1answer
236 views

Physical interpretation of distances

Suppose we have a universe with only two distinguishable particles, neglecting gravitation. These particles start off next to each-other, ostensibly "touching" each-other and at rest. If it takes ...
2
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4answers
61 views

Is the concept of work only defined in mechanics?

I'm studying energy and work, so far it looks like work only makes sense in kinematics (objects that move), but energy makes sense in many other ways (electric, thermodynamic, mechanic). Is work a ...
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0answers
82 views

Finding the stored potential energy in a uniformly charged solid sphere

my question is finding the energy stored in a charged solid sphere. I believe I have the correct answer with: E=(4π/3)ρR^3 A uniformly charged solid sphere has a charge density ρ and radius R. Find ...
0
votes
1answer
34 views

surface charge on a resistive wire in dc circuit

I want to understand how does the energy transfered from battery to the resistor in a simple dc circuit . I readed that it is due to the surface charge the battery creats on the wire . So why this ...
3
votes
1answer
54 views

Energy in a sound wave possible error?

In a certain text discussing longitudinal waves it stated that for a sound wave, both the kinetic energy and potential energy are maximum at the same time. I always thought that the potential energy ...
3
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3answers
7k views

Finding the max height of a ball launched as a projectile using work-energy

A ball is launched as a projectile with initial speed $v$ at an angle $\theta$ above the horizontal. Using conservation of energy, find the maximum height $h_\text{max}$ of the ball's flight. Express ...
-2
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1answer
107 views

Ground state energy of spin 1 particle

So I have this Hamiltonian for a particle with spin 1: $$ H=aS_{z}^2+\frac{\hbar\omega}{\sqrt2}S_{x}$$ where ($a$ and $\omega$ both real constants): $$ S_{z}=\hbar\begin{pmatrix} 1 & 0 & 0 ...
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2answers
7k views

Why can't we destroy energy?

From a wikipedia article: In physics, the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. Energy can be neither ...
1
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3answers
66 views

What is the relation between Force, Physical Strength,Enery and Work?

I am sorry ,but, I am not much of science or a physics guy, if this question sounds stupid. Anyways, what is the relation between all of them. Like for example, does applying more force means more ...
0
votes
2answers
134 views

Conduction bands and Valence Bands, so do electrons really exist in Conduction bands?

My understanding is that conduction bands are energy bands created from the electrons in the valence shells/bands absorbing energy to jump to the next level (is this true)? Now, do the conduction ...
0
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0answers
25 views

The velocity of the charged particle in the magnetic field [duplicate]

Enrico Fermi considered that moving charged particle gains energy in the magnetic field, so its velocity increases. According to the Lorentz Law $\vec F=q\vec v\times\vec B$. Work is $A=\vec ...
1
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1answer
137 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
6
votes
1answer
208 views

How do I describe and calculate the effect of an impacting object?

My lab studies the physiology of impact injury on biological tissues. I use a pneumatic cylinder to impart injury into a biological sample and then assess the molecular and physiological changes in ...
10
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3answers
839 views

Do human bodies give off a consistent but unique radiation/electromagnetic/energy signature?

Is there any facet of the energy emitted by a human body that is consistent and unique - like a fingerprint, but a signal that could be detected by a remote device?
1
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1answer
27 views

Conservation of energy in a sound wave

I have two ultrasonic transducers, an emitter and a receiver, and I'd like to know how the energy of the spherical wave is conserved. I guess the energy is proportional to its amplitude and it ...
2
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2answers
131 views

Regarding (regular) kinetic energy and rotational kinetic energy

In my physics class we saw this problem: A disc of mass $M$ and radius $r$ is standing vertically and can rotate freely through an axis thats goes through its center of mass. A small particle of ...