# Tag Info

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A sphere made of an electron-rich element/molecule is placed within a nuclear reactor. The basic flaw is that Uranium is also a metal so no charge would build up. Insulators would melt in the reactor so the process is no go. If one could insulate with a vacuum (for example) the sphere would gather energy through a surface, a very small part of the ...

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You should look into direct energy conversion. Stanley Angrist's "Direct Energy Conversion" is a solid book on the topic. Additionally Ralph Moir, William Barr, and George H. Miley, have done significant work in the field, and have many interesting publications, though admittedly with applications to fusion power.

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None. A force doesn't require energy. The wall spends no energy in just holding back. Just like a table spends no energy in simply holding up a book. The human body is complicated. In order to be able to apply the pushing force, muscles will contract etc. This requires energy. But this is not a general rule.

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I noticed today that the water warmed up in pressure cooker (1.5 ATM) dissolves sugar much faster and much more than water cooked in 1 ATM. The effect you observe is one of temperature, not pressure. Water soluble substances dissolve quicker when the temperature is higher because the water molecules of hotter water have a higher average kinetic energy ...

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Basically yes. Firstly instead of your dispersion relation you must now use that $E = \hbar \omega$ and that $p = \hbar k$, then your new dispersion relation (valid for energetic electrons) is $$\omega = k c$$ and the result follows.

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Potential energy like Force occur in pair. If one has some potential energy due to 2nd, 2nd will have the same potential energy as the first. In the Gravitational potential energy equation : $U = \frac{GMm}{r}$ The potential energy is dependent on both the masses. This value is same regardless whether it is for 1st or 2nd. Both the body can do Same amount ...

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Particles have gravitational potential energy due to its position in the gravitational field. Systems have potential energy. Ascribing the energy to a particle is incorrect. We say the particle has potential energy and not the Earth (the body doing the work). That is incorrect. The potential energy is a function of the system, specifically the ...

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Potential energy is just energy stored in a static state -without motion. So a spring can have potential energy, and so can a body attached to the spring that's in a gravitational field. So for this type of system (undamped harmonic oscillator in a gravitational field) potential energy is not strictly defined for the spring. If the forces are conservative ...

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There are a couple things missing. The normal forces corresponding to the friction forces $F_1$ and $F_2$. Specifically $F_1$ as the velocity is not perpendicular to the force, so it can be used to do work transferring energy from one disk to the other. Conservation of angular momentum about the red dot. This can be used to figure out the final angular ...

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The connection of frequency to energy comes when one considers the covariant formulation of the electromagnetic wave propagation. In Panofski and Philips "classical electricity and magnetism" second edition chapter 21. This quote in particular. This associates a zero mass particle with a fourvector, i.e. energy and momentum . Text goes on to explain ...

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it seems to me indeed strange that electrons get more energy by a higher frequency Why is it the high-frequency part that bothers you? Classically, high frequencies imply more energy. An example you might consider is whacking a ball-- the faster it spins, the higher it's frequency and the more rotational energy it has. More relevant, high frequency ...

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The motion can be broken down into four phases. The first phase is simple: the reel starts pulling in on the line, forcing it to slide around your finger (as it would if you slowly let it reel in), with the reel pulling the line in as fast as it unwraps from your finger. There are two forces on the reel: the pull inward of the line, and the push outward of ...

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This is an interesting phenomenon and one that can be explained as follow. Inside the reel is a torsion spring that stores potential energy. When the string is fully furled up inside the reel (around some narrow cylinder), the potential energy is minimum (almost zero) because the torsion spring is almost tensionless. But when you pull the string out of the ...

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So the internal energy $U$ of a system is subject to a thermodynamic relation which looks like $$dU = T~dS-P~dV+\sum_i\mu_i~dN_i$$where $T$ is the temperature, $S$ is the entropy, $P$ is the pressure, $V$ is the volume, $N_i$ are the number of atoms of various species $i$, and $\mu_i$ are their chemical potentials. You can view this as a definition of ...

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TS is not energy it is the product of temperature and change in entropy of the system

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As far as I know, there is zero physics in "Crystal Energy", which if I understand what you mean, is related to Crystal Healing. There is a good bit of validity to the placebo effect and belief, so a person believing in something, whether the practitioner or the patient, can have an effect or the impression of an effect, but that's not physics either. ...

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Crystals have internal energy including some energy associated with molecular vibrations. Amorphous materials have internal energy including some energy associated with molecular vibrations. In addition to molecular vibrations, crystals can exhibit mechanical (macroscopic) vibrations. An example of a resonant macroscopic vibrator is a tuning fork. But, ...

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See, a crystal due to its temperature and through various media can be made to vibrate. Now because of the fact that the atoms(lattice points, could be molecules too) are connected with each other, the vibration actually spreads in all directions. Thus this vibration acts as an wave. But the whole of crystal, because of its structure can vibrate only in ...

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When you heat water you increase the kinetic energy of the water molecules. As an order of magnitude estimate, the kinetic energy at a temperature $t$ is about $kT$, where $k$ is Boltzmann's constant. So when the molecules in water (or ice or steam) interact with each other the energy available is roughly $kT$. At the temperature of boiling water this ...

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Assuming you mean the enthalpy of combustion, carbon dioxide doesn't combust. That is it does not react with oxygen to produce water and carbon dioxide. Therefore it has no enthalpy of combustion. Did you mean carbon monoxide?

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What's wrong is that you started with the waves $\pi/2$ out-of-phase. They should be in-phase, as this description shows, otherwise they will not obey the Maxwell Equations and you cannot use Poynting's Theorem (which itself is derived from the Maxwell Equations): Image credit: nde-ed.org. Doing out the expression with $E \propto \cos(\omega t - k x)$, ...

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Your question could use a context to be more clear. But I think you mean that the battery supplies a certain $\mathrm{emf}$ to the circuit, and the circuit elements require a certain voltage $V$ for the current to run. Now, if the voltage $V$ over all circuit elements (summed up) is less than the $\mathrm{emf}$ supplied, then some is lost. Meaning, some ...

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Your question makes no sense. Volts is merely a common unit EMF is measured in. To say that volts means a different kind of energy per charge than EMF is just plain wrong, making your question non-sensical.

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Consider the following free body diagram: The net force acting on the body along the surface = $mg \sin x$ Therefore, the net acceleration in that direction is $g \sin x$. So the velocity of the body at a time t after starting to slide down the inclined plane is $v = gt \sin x$ So, K.E. (kinetic energy) of the body is $$\frac{1}{2}mv^2 = ... 4 The conserved mechanical energy is: E=KE+V=KE+mgh where h is the height of the body. As the body slides down due to the acceleration of gravity, the distance travelled would be d=\tfrac{1}{2}a{{t}^{2}}, where a is the acceleration caused by the addition of the weight of the body and the vertical reaction force. If L is the length of the inclined ... 0 Its a graph of y = {v(t)}^2= kt^2. Graph of x^2 is: When the object moves down from the top, it gets accelerated due to gravititional force or its component so its velocity changes(increases) instant after instant; this means v^2 in \frac{m}{2} v^2 is a function of time squared. Thus, the variation of KE is a square. 2 Well, actually it doesn't. Knowing the wavelength allows you to calculate the energy, but it does not "determine" it in a causal way. Energy (E), wavelength (\lambda) and frequency (\nu) are related by$$E = h\nu =\frac{hc}{\lambda}$$so if you know the wavelength or the frequency you can determine the energy. I think his use of "determine" confused ... 2 Why does the wavelength determine a photon's energy? In the 19th century, it was thought that the energy of light was determined only by its intensity. Then, experiments, particularly the photoelectric effect, showed that this was not so: a low-intensity short-wavelength light can cause reactions that intense light of a longer wavelength cannot. Thus, ... 0 Just as the energy levels in a hydrogen atom are associated with the hydrogen absorption or emission spectrum, you can think of the energy levels in an infinite well as associated with the absorption or emission spectrum of a quantum dot (quantization in 3-D), quantum wire (quantization in 2-D), or quantum well (quantization in 1-D): The difference between ... 0 How does a molecule form? At the most general level the idea is that there exist lower energy states with the atoms in the molecule closer to each other, and the original joint state of the atoms had a nonzero ability to transition into that lower energy state and give up some energy. The rest is really some thermodynamics. If everything is hot and dense ... 0 I am not sure whether it is true that the ADM energy depends on rest mass. But if it is true, an object with zero rest mass generate no gravity such as plane electromagnetic wave. The property of plane gravitational wave is analogous to plane electromagnetic wave, so it should has zero rest mass as well. You can apply it to gravitational solitons (a wave ... 3 Conservation laws are intimately connected with symmetries. This was proved by a mathematician called Emmy Noether in 1915 and is called (not unreasonably) Noether's theorem. The only assumption required is that the system can be described with Lagrangian mechanics. In particular conservation of energy is related to a symmetry called time shift symmetry. ... 0 All I can think of is EEG (electroencephalography) signal. It is a diagnostic technique that allows to monitor brain electrical activity by measuring potentials on the scalp. As I know there are some contactless methods of measuring those potentials, but I have no idea if you can measure it from big distance, since it is quite a weak signal. This is one ... -1 This (ideal) device is a small variation of Maxwell's demon. It is believed that Maxwell's demon violates the second law by decreasing the entropy of the universe (isolated system). However, that is not true; Maxwell's demon violates the first law of thermodynamics. See http://vixra.org/abs/1310.0181. Your machine leads to violation of the principle of ... 2 That's what the muffler does, as you learn the first time you have a car with a muffler that gets damaged. The essential difference between gas and electric cars is that the gasoline power is derived from a carefully timed sequence of small explosions, in the pistons; the electric car does not have this phenomenon and will always be quieter for the same ... 2 If initially the mass is at x=0 and the initial velocity is V then the (underdamped) position response is:$$ x(t) = X \exp(-\beta t)\sin(\omega t) = \frac{V}{\omega} \mathrm{e}^{-\zeta \omega_n t} \sin(\omega t) $$where$$\begin{aligned} \omega_n & = \sqrt{\frac{k}{m}} \\ \zeta & = \frac{d}{2 m \omega_n} = \frac{d}{2 \sqrt{k m}} \\ \omega ...

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In Newtonian Mechanics, the work-energy theorem states that net work = change in KE (not in PE). Let's consider an example. Imagine a block of wood falling down on a rough ramp. The non-conservative force here is friction, and the conservative force is gravity. On a frictionless surface, gravity converts PE into KE while conserving the total energy. ...

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Your question seems to arise from a problem in which there is both a conservative and a non-conservative force. When you say "PE" you must be referring to the PE of the conservative force (by definition there is no PE of a non-conservative force). The work done by the conservative force does not depend on the path. Therefore you can define the potential as ...

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It seems to me you are making this more complicated than it needs to be. When the cable first becomes taut, the spring force is not yet in play and the only force will be $v\cdot k$ - by the definition of the drag in the dash pot. You can compute the subsequent motion by solving the damped harmonic oscillator. Let me know if this is enough?

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No, the cited equation is not justified by the relativistic energy formula in the derivation the OP asks about. The corresponding text of the derivation is as follows: For the momentum of our photon, we will use Maxwell’s expression for the momentum of an electromagnetic wave having a given energy. If the energy of the photon is E and the speed of light ...

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The general Energy equation is $$E^2 = (mc^2)^2 + p^2c^2$$ where m is rest mass. Since in case of photon rest mass is 0. So we will get $$E = pc$$ $$p = E/c$$

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Well, if you accept energy-momentum conservation, then the equation you referred to can be easily obtained from the energy-momentum relation of E^2=(p c)^2+(mc^2)^2, where E is the energy of the particle, p is its momentum, m is its rest mass, and c is the speed of light (see Energy–momentum relation). For photons, the rest mass is zero, so this equation ...

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The Foucault pendulum motion is induced via the Earth's rotation. Because it moves it can perform work. I answer Yes, but irt others it may depend on the more or less flexible definition of vast amount and the size and number of pendulums . EDIT ADD to 'debunk' myself: The above statements are correct,imo, but I will decompose the situation. Some ...

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The shorter the wavelength of the electromagnetic wave the more energy it carries, when it hits an atom and gets absorbed the electron gains kinetic energy and jumps to higher energy state. This happens only if the energy of the photon is equal (within the width of the energy levels) to the difference between the energy levels. The "gaining kinetic ...

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According to Stephen Hawking in 'A Breif History of Time', the total energy of the universe is zero. That's because there's negative energy associated with gravitational attraction. Add positive to an equal amount of negative, and you get zero. So saying energy can't be created or destroyed just means you can't change the total energy of the universe, which ...

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In his excellent answer John Rennie gives the numbers. If this sounds incredible, A more intuitive approach that indicates that's roughly in the correct ballpark is to take a look at strongman pulling contests. https://www.youtube.com/watch?v=hP00VmKx_No shows you a dude pulling a 150 tonne train. He's not going particularly fast, but still, he's moving at, ...

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(v) I then differentiate this by $v$: $t$ = $d'(v)$ =$\frac{mv}{k\sqrt{A^2-\frac{mv^2}{k}}}$ (am I crazy?) You made a mistake, $\frac{d}{dv} d(v)$ doesn't equal time. For instance, $\frac{d}{dv} d(v)$ can be the same at two different times. Consider the simplest case, a particle is at rest. Then $v=0$ and $d(t)=const$ so the derivative either ...

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The energy needed to stop a train is the energy needed to open the air brake valve and let the air out of the air brake system (at least with US trains). It's hard to guestimate the amount of energy required to do this, but I'd guess to turn even a moderately stiff lever would require significantly less than one kilogram-meter == 9.8 joules. The kinetic ...

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The reason is that $\lambda$ is a decreasing function of $\nu$, so that if $d\nu$ is positive then $d\lambda$ is (at least formally) negative, but we explicitly want to not care about that. We want $u(\nu,T)d\nu$ to be the energy content per non-directed unit frequency, and ditto for $w(\lambda,T)d\lambda$, and the absolute value ensures that that is the ...

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I believe he is wrong, but not about the number. From @JohnRennie answer we see the energy of the cookies is roughly equal to the train's kinetic energy, so we need such amount of energy to accelerate the train to this speed. However, Energy to stop train... Energy , or work required to stop a train generally doesn't equal to the train's kinetic ...

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