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

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). ...
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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 ...
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27 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 ...
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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 ...
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1answer
43 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 ...
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0answers
42 views

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

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 ...
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1answer
32 views

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

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 ...
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1answer
27 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\{ ...
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27 views

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

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? [on hold]

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?
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2answers
63 views

Blocks releasing heat energy [on hold]

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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1answer
96 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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0answers
48 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 ...
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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 ...
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4answers
60 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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2answers
53 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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3answers
65 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 ...
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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 ...
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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 ...
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4answers
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Why does an electron shell further away from nucleus has higher energy level?

Using electrical potential energy $V=\frac{1}{4\pi \varepsilon_0} \frac{Q_1 Q_2}{r}$ , a particle further away from nucleus has lower magnitude of energy. Using Coulomb's law, a particle further away ...
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2answers
46 views

Is flow energy the same as work?

Studying thermodynamics I face this following text from Cengel's book. Throttling valves are usually small devices, and the flow through them may be assumed to be adiabatic (q = 0) since there is ...
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0answers
46 views

What is the cause of discrete or quantized energy levels in an atom? [duplicate]

I understand how it is that electrons move from one energy state to another, however I've not been able to find anywhere that describes why an atom has any particular states. Why should an atom of ...
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2answers
44 views

Why did Trebuchet have so long throwing arms?

Have a look at such an historical Trebuchet: As you can see, the throwing arm (left) is much longer than the weight arm (right). Law of conservation of energy says, potential energy from the ...
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1answer
28 views

What happens if a cylinder filled with propane gas is connected to an empty one of the same size

Lets say I have 2 100lb propane cylinders. One of the cylinders is filled to its maximum capacity while the other is empty. If I connect them to each other via a high pressure hose in an upright ...
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3answers
134 views
+50

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 ...
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1answer
25 views

How high does a slide need to be if the person at the bottom grabs a pole and rotates the pole 72 degrees?

My attempt: $mgh = \frac{1}{2}I \omega^2$ $\omega^2 = 2 \alpha\Delta \theta$, so $mgh = \frac{1}{2}I 2 \alpha \Delta \theta$ $mgh = I \alpha \Delta \theta = \tau \Delta\theta$ $\tau = rF\sin ...
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1answer
101 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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1answer
17 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 ...
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0answers
25 views

Why is light redshifted?

I heard that very distant stars can be seen as red. Why does light become more 'redder' when travelling long distances? My guess would be it loses some sort of energy, but can't seem to figure it out ...
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2answers
86 views

Basic Classification of Energy [closed]

When I was still in school, I learnt that there are 2 types of energy: Potential & Kinetic Energy. When I searched Wikipedia and other sources, there were many forms of energy. There are some ...
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1answer
52 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 ...
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1answer
49 views

Intelligence and Entropy [closed]

Is intelligence an entropy transformer? and the difference between a lower and higher intelligence is the efficiency?
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1answer
54 views

How energy would be consumed for bending spacetime?

If we could assume that relativity theory is correct about spacetime bending. Can we calculate energy used for moving 1 kg of object in 1 meter by changing the shape of spacetime (simulate gravity)? ...
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How can I measure energy dissipation in Magneto rheological Fluid dampers?

I have a problem which is related to the energy dissipation in the Magnetorheological Fluid dampers for vehicle. I have MR damper with displacement and velocity sensor to get the data of vertical ...
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0answers
15 views

Fuel energy density vs power output

I've had this problem forever, and I'd finally like to get it resolved. Suppose one has two identical engines, One and Two. Engine one is run on a fuel with energy density X, which we'll call Fuel ...
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1answer
33 views

Energy of photon after emission

Exercise: A hydrogen atom is at its first excited state. When it de-excites it emits a photon. What is the energy of the photon and the kinetic energy of the atom? Question: Is it correct to ...
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23 views

Rotational energy of a celestial body

Let $M=2.8\cdot 10^{30}$ be the mass of a celestial body. We know that each year (earth year) his period increases by $11\mu s$. The power we receive of the radiational fog is $5\cdot 10^{31}W$. The ...
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28 views

Mechanical energy in an harmonic wave and in normal modes

I think I miss something about energy of a mechanical wave. In absence of dissipation the mechanical energy transported by an harmonic wave is constant. $$E=\frac{1}{2} A^2 \omega^2 m$$ But, while ...
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53 views

Proof for fluctuations in vacuum

I'm not a physicist. My understanding of Heisenberg's uncertainty principle and its proof (that is given by an imaginary microscope) is that for example: at a specified time determining the exact ...
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0answers
53 views

Energy of a particle as measured by an observer at infinity

I'm wondering if it is possible to make a definition for the energy of a particle as measured by an observer at infinity. I've looked through Wald for this but wasn't able to find anything - I may be ...
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1answer
33 views

change of energy in changing frame of reference

Let's imagine a car that can jump onto, or off a moving train. The train moves at 10m/s. The car, on a road next to the train, accelerates to the same 10m/s, jumps off a ramp and lands on the train, ...
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4answers
45 views

How can removing energy from a system do work? (ice)

Water freezing into ice expands, damaging roads, breaking rocks, etc. To my understanding, this is doing work (in a physics sense) by removing energy from the system. How is this possible?
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34 views

how to calculate enthalpy and internal energy in relation to heat capacities?

I remember that $\mathrm du=c\mathrm dT$ and $\mathrm dh=c\mathrm dT$ with $c$ being two different heat capacities, but I can't find anything about it, any help?
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2answers
60 views

What is beyond Gamma Rays and Radiowaves in the Electromagnetic Spectrum?

The electromagnetic spectrum is commonly refered to as consisting of; Radio-waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays - of increasing frequency from left to right. ...
3
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1answer
60 views

2 times the velocity, 4 times the energy, 8 times the heat

In SpaceX's webcast today they talked about the first stage getting back to Earth with twice the velocity as usual. I quote: "So 4 times as much energy means harder on the stage, and 8 times as much ...
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0answers
16 views

What is the energy density of a spinning orbiting ball of uniform mass with surface charge?

What is the energy density of a spinning orbiting ball of uniform mass with surface charge? I know that all the energies involved are mass-energy, spinning energy, orbiting energy, electric energy ...
2
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1answer
60 views

Work done in bringing down a body [closed]

A block of mass $30$ kg is being brought down by a chain. If the block acquires a speed of 40.0 cm/s in dropping down $2.00$ m, find the work done by the chain during the process. I have calculated ...
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3answers
65 views

how could Kinetic energy increase if no energy was there in the system?

i was reading Physics-Halliday, Resnick, Krane(fifth edition) there on page 638 it is written: if the external agent does positive work in assembling the charge ...
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1answer
53 views

Why is standing still easier than walking? [closed]

Both the works basically push force into the ground.So why does walking require more work?
5
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1answer
52 views

Understanding potential energy

I am self-studying the classical mechanics using the book by Taylor, and I have a question about the potential energy. The book (pg 111) says: If all forces on an object are conservative, we can ...