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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Energy of a permanent magnet railgun

I'm creating a permanent magnet railgun, which essentially uses two conducting rods with a row of magnets between them and a conducting projectile laying across the two rods. I am trying to determine ...
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2answers
64 views

Mass hanging from spring: potential energy [closed]

I have encountered a problem with a mass $m$ hanging from a spring. I want to find the maximum distance it will be stretched from the spring's equilibrium. At the maximum distance the spring is ...
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Why on a frictionless incline, a rolling object reaches the bottom slower than an non-rolling object?

I am really sure if what my physics teacher told me was correct. But he said, rolling objects has rotational kinetic energy, so not all potential energy they have at the start is converted into ...
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Kinetic energy formula from nonzero initial velocity

Do I then have to use: $$\frac{1}{2}m(V_f^2-V_i^2)$$? I am assuming I should use this formula for change in kinetic energy if the object under examination doesn't start from rest.
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What form of energy is magnetism stored in?

In physics class I was told that there are 9 forms of energy: -Electrical -Light -Thermal -Nuclear -Elastic Potential -Gravitational Potential -Sound -Kinetic -Chemical So, my question is, ...
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1answer
74 views

How much work can the human body do before dying of exhaustion [closed]

If we could assume: We don't increase our energy from absorbing food. Our human example in scope isn't starving or suffering from malnutrition. I mean how much work can we do until the body would ...
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2answers
49 views

Inconsistency with electrostatic energy formulas

The energy of point charge configuration can be written as: $$W = \frac{1}{2}\sum_{i=1}^{n}q_{i}V(r_{i}) \, ,$$ which can take both positive and negative values. However, when we integrate the ...
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1answer
32 views

Plausibility of the distance estimation in a cycle ergometer gym exercise

A friend of mine pedaled for an hour on a cycle ergometer, a stationary bicycle in a gym. At the end of the ride the cycle computer reported a distance of $40\:\mathrm{km}$ and an average power of ...
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0answers
73 views

Will the block #3 move? [closed]

Hey, On my test I've been assigned to calculate acceleration of the box with mass = m3(I'll call it block #3). The problem is, I can't even imagine the block moving, as I cannot find any force ...
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0answers
35 views

Formulae for Elastic Hysteresis of rubber

Being a school student, I'm pretty sure we don't need to explicitly learn any formulae helping us evaluate the energy dissipated by mechanical internal energy in a hysteresis loop. But I was wondering ...
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1answer
35 views

Kinetic energy of fluid + collision

When a fluid is flowing, it has of course a kinetic energy and thus we can define kinetic power equal to ρAv v is the velocity and A is the surface of a solid for example. I have a question (maybe it ...
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1answer
21 views

Reverse particle accelerators! [closed]

If we are tearing matter apart in accelerators, why can't they reverse the process? Apply energy at one end and take matter out of the other. When energy first changed to matter in the Big Bang, ...
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1answer
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Kinetic energy during 1 minute - wrong? [closed]

I've come across this IEEE paper whilst researching for a project I've undertaken regarding a bicycle generator. This paper concerns an exercise bike powered electric generator. Essentially they have ...
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1answer
77 views

Why are harmonic oscillators quantized? [closed]

What physical reason is there for a mass on a spring to have discrete energy levels? And why are those energy levels equally spaced, i.e. why is $E \ \alpha \ f$? Personal background and ...
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0answers
21 views

Does matter shrink due to energy radiation and does it have anything to do with dark matter and dark energy?

Is matter shrinking? Is shrinking the cause of concentrated dark matter that makes up matter moving from concentration to unconcentration. Does dark energy and expansion of the universe come from this ...
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1answer
28 views

anatomy of combustion

I don't understand how energy is released in combustion. We have a reaction of a combustible material with oxygen and this releases energy. In what form is this energy released? It should be some ...
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1answer
49 views

Energy paradox in fluid mechanics

In a fluid, the specific mechanical energy $$e_{mech}= \frac{P}{\rho} + \frac{v^2}{2} + gz$$. Where $P$ is the static pressure, $\rho$ is the density, $v$ is the velocity, $g$ is the gravitational ...
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0answers
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Perturbation Theory Question

How can you work out the average perturbation, from a normal hamiltonian, of all states that rely on the quantum numbers of s = __ and l = __, with the perturbation being proportional to the product ...
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3answers
104 views

Power statement is valid for MW Or KiloWatts? [closed]

If I can talk to someone and tell him that a new power plant inaugurated by Prime Minister will produce $60$ megawatts per hour, will it be true to use $\mathrm{MW}$ unit for Power?
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1answer
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Particles, quasiparticles, and “stability”?

So I'm studying Fermi Liquid Theory, which concerns itself with quasiparticle excitations made by superpositions of single-electron wavefunctions. We create particle-like wavepackets which exist for ...
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0answers
33 views

Turning an engine over with engine compression [closed]

When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well? if you ...
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2answers
39 views

Energy release on impact

I was watching this video from a video game showing a space ship travelling towards a planet at 22% the speed of light. The ship system pulls the ship out of this "quantum travel" just in time to ...
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1answer
26 views

Total reflection in a solar collector?

So, I was wondering how radiation is kept inside a solar thermal collector? The sun light (or its photons) penetrates through the glass and is then absorbed by the absorber layer. In turn, the ...
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1answer
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how is the state parameter determined?

For radiation, dark energy and dust the pressure and energy density are related, respectively, by: $p=\frac{1}{3}\rho$ $p=-\rho$ $p=0$ My question is why? How does one show that this is how ...
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0answers
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Finding the distance a spring travels [closed]

So you hold a spring in your hand. You know that if you attach a 0.100 kg object that it will stretch the spring 0.05 m. The spring is launched off your hand(1.25 m off the ground) at a 35 degree ...
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2answers
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Can wifi signal reception be improved by opening a door? [closed]

Use Case A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal. Engineering Question Can the wifi signal from the router to ...
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0answers
28 views

Kinetic energy expressed with angular velocity

I'm studying the chapter Energy on Kleppner's book. There we have an example of a Conical Pendulum. It is said that it moves with constant angular velocity $\omega$ in a circle of constant radius ...
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1answer
27 views

Heat absorbing then releasing material [closed]

I want to create a piece of sculpture That absorbs the suns rays in my family room during the day and released the heat in the evening. What would be the best material for this? I was thinking a ...
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2answers
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Question about spring force and work [closed]

An ideal massless spring can be compressed $2.33\ \mathrm{cm}$ by a force of $268\ \mathrm{N}$. A block of mass $m=3.18\ \mathrm{kg}$ is released from rest at the top of a frictionless incline of ...
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1answer
58 views

Comet's distance with and without gravity [closed]

I've got this question that I just can't seem to answer. The question is as follows: A comet approaches the solar system with velocity v and would, if the sun would not attract the comet, pass the ...
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1answer
41 views

Does a weight attached to a string over a spinning pulley count as a transfer of kinetic to rotational energy?

More specifically, if I had a weight hanging on one end of a pulley at some height h (the other end of the string continues onto another pulley) and I let it go, would the kinetic energy gained from ...
2
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1answer
100 views

How does hydraulic press work at molecular level?

Let's consider the following arrangement: I know that because of conservation of energy the force on the car has to be amplified. The work $W$ done is $$W = \text{Force} \cdot \text{distance} \, ...
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2answers
74 views

How can Work and Kinetic Energy have the same units?

If work is Force x Displacement, it would result to N x m, which is Joules. But then, kinetic energy is 0.5mv^2, which is kg x m^2/s^2. Can anybody tell me a way to prove that they have the same ...
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81 views

How is frequency related to kinetic energy?

Does producing higher frequency waves require more energy than their low frequency counterparts with same amplitudes? For example, in electronics, would a 500 kHz wave require higher voltage to ...
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1answer
56 views

Total energy of a simple pendulum proportional to the square of the amplitude? [duplicate]

It is known that in simple harmonic motion, the total energy of the system is proportional the square of the amplitude, but how can I prove that for a simple pendulum where amplitude is the arc length ...
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1answer
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Relation of Force and Energy, from a biophysics point of view

Considering us humans practically, does energy require force, ie we do apply some internal and external forces to do work, or does force require energy. ie we can only apply a force on an object if we ...
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2answers
41 views

System of potential energy

Is potential energy calculated between a system? More specifically, if we say 'potential energy of a ball with respect to earth', does it mean that the Earth + the ball is a system?
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71 views

Conservation of Mechanical Energy Before and After Impact of a Hammer

If a hammer does work by driving a nail into a wooden board, how does the mechanical energy from right before the hammer hits the nail compare to the mechanical energy after the nail has been driven ...
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0answers
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Speed of an antimuon in a pi meson decay [closed]

I'm trying to confirm the speed of an antimuon in the $ \pi^+ \rightarrow \mu^+ \nu_{\mu}$ decay through the laws of conservation but it doesn't add up. I'm using $m_{\pi} = 139.6 \ \frac{MeV}{c^2}$, ...
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1answer
93 views

Parkhomov's E-cat reproduction [closed]

In the beginning of the year, Professor Alexander Parkhomov of Lomonosov Moscow State University claimed to have replicated (as read in e.g. Wired) of the E-cat functioning, albeit with lower effect. ...
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1answer
76 views

Why is thinking not considered as work? [closed]

While thinking the impulse in our neurons displace and they move in direction of force applied on them. Here the force is applied and impulse moves in direction of force ie it is displaced. Then, why ...
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1answer
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Is there a principal difference in acceleration from an impulse and the free fall of a body in the orbit around a gravitational mass?

Especially taking in account that acceleration need a force which leads to some conversion of energy. This is not the case for orbital motion, such a acceleration does not convert energy. That seems ...
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0answers
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Help with a problem in magnetism, kinetic energy

I couldn't fully understand how the author solved the problem c). Here's what was done: At first I thought he changed $v$ for $\sqrt{\frac{2K}{m}}$ in the equation $r=\frac{mv}{|q|B}$, but ...
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5answers
139 views

Does gravity acting on a resting object produce any heat?

Let's compare two systems. System 1: A box is completely isolated. There are no forces acting on that object, and no interactions of any kind with other objects, waves, etc.. System 2: The same box ...
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1answer
79 views

Infinite potential well question with wave function $\psi (x) = (x -a/2)^2$

In an infinite potential well with width $a$, a particle in this potential well is at state with wave function is $\psi (x) = (x -a/2)^2$ (not normalized). If you measure the energy of ...
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1answer
45 views

Is it possible to ascend (or descend) an escalator, without consuming any more power produced by the motor of the escalator?

Is it possible to ascend (or descend) an escalator (which ascends with a constant speed), without consuming any more power (energy) produced by the motor of the escalator ? I mean, find a way to walk ...
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1answer
42 views

Understanding energy and its transfer

Basically the concept of energy is confusing because in all other cases like velocity or mass I can see and clearly imagine whatever changes happen but when somebody says energy got transferred from ...
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2answers
57 views

Energy forms of a charged particle in an electric field?

I am thinking an explicit list of all energy forms in a system of charged particle (take electron or proton, for instance). It has at least potential energy and kinetic energy by Newton. ...
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6answers
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Energy and its physical significance

What does it exactly mean when we say that energy has moved from one body to another, what has physically been transferred? The concept of energy is very confusing, please help. And if gravitational ...
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0answers
25 views

FD Statistics - average energy derivation in terms of fermi energy [closed]

I need to derive an expression for $\langle \epsilon^n\rangle$ of an electron in terms of $\epsilon_F,$ for $T\ll T_F.$ Would appreciate some help. Thanks!