Energy is a quantity which gives an overview of the amount of work doable by the system.
1
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0answers
35 views
Any examples of negative ADM energy solutions with WEC but not DEC satisfied?
Any examples of negative ADM energy solutions with weak energy condition (WEC) but not dominant energy condition (DEC) satisfied?
Witten's proof of the positive energy theorem requires the dominant ...
1
vote
2answers
263 views
Maxwell-Boltzmann distribution and total energy per unit volume
We know that
$$n(E) ~=~ \frac {2 \pi (N/V)}{(\pi k_B T)^{3/2}} E^{1/2} e^{-E/(k_B T)} dE,$$
where $V$ is total volume.
If then, how do we derive total energy per unit volume from this equation?
0
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1answer
88 views
Why are there two ways to solve for energy of a spring?
I can find the energy of a spring using $F = -kx$, or by using the formula $e = 1/2mv^2 + 1/2I\omega^2 + mgh + 1/2kx^2$. The first way, I get $mg/k = x$, but the second way, I get $2mg/k = x$. Which ...
0
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0answers
37 views
What gives photons their energy? [duplicate]
Possible Duplicate:
Does $E = mc^2$ apply to photons?
I've been to a presentation by a CERN scientist, and he briefly talked about photons. It was stated that photons have different energy ...
0
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0answers
93 views
Energy efficiency Vs power efficiency
I want to understand if there can be any real difference between the requirement of Energy efficiency and the requirement of power efficiency for a physical system. For example for CMOS-based digital ...
0
votes
2answers
205 views
Does the potential energy related to a particle determines its rest mass?
Would it be possible to determine the rest mass of a particle by computing the potential energy related to the presence (existence) of the particle, if this potential energy could be determined ...
2
votes
0answers
69 views
Is there some connection between the Virial theorem and a least action principle?
Both involve some 'averaging' over energies (kinetic and potential) and make some prediction about their mean values. As far as the least action principles, one could think of them as saying that the ...
1
vote
1answer
86 views
Where is the critical moment where the microcanonical ensemble enters the justification for the equilibium state?
As explained in many books, for the microscopic justification of the second law of thermodynamics (lets formulate it as the total entropy takes maximum among all possible exchanges of two systems), ...
6
votes
4answers
156 views
Is energy extensivity necessary in thermodynamics?
Given a partition of a system into two smaller systems, the energy $U$ is devided into $U_1$ and $U_2$, with
$$U=\mathcal{P}(U_1,U_2):=U_1+U_2,$$
so that $U_2$ is given by $U-U_1$. Here the ...
1
vote
1answer
108 views
Inefficiency Comparison of Car Air Conditioning vs. Open Windows
On a recent long, hot journey in Spain, I was pondering which was the most efficient way of cooling the car. Which of these would be the most effective?
Switching on the air conditioning, thereby ...
0
votes
1answer
88 views
What is the most energy-efficient way to crush the hardest bedrock on earth?
What is the most energy-efficient way to crush the hardest bedrock on earth while assuming it is impossible to use the chain reaction energy from that bedrock?
How many energy is needed?
3
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1answer
279 views
The possibility of free electrical energy?
Please excuse my lack of knowledge/understanding.
Question: Why Nikola Tesla's Free Energy concept was never worked upon? Even today.
Context: Now that we know Nikola Tesla was a genius and did ...
0
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2answers
178 views
From where does the force/energy of action-reaction comes from? (Newton's Third Law of Motion)
I was wondering, from where does the opposite force and thus energy comes from when we apply force.
For example, lets say there are two persons (P1 and P2) on the universe, and no force is applied to ...
2
votes
2answers
358 views
Is the potential energy in a compressed spring a Lorentz invariant?
The total energy of an object comes from the time part of the four-momentum, and so isn't a Lorentz invariant. On the other hand, is the potential energy of a compressed spring a Lorentz invariant?
-1
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3answers
462 views
Relation between Newtons and Kilograms
Work is expressed as W=F*d, where the F is in Newton, d is in meters and result ...
0
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1answer
43 views
Which particle rolls faster? Is the speed of the particles which are rolling differs with their shape?
A solid disk and a solid sphere each of them has the same mass and same kinetic energies, which one is faster?
-1
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2answers
278 views
How we can find the kinetic energy? [closed]
A solid disk of mass m is rolling along a surface its center has velocity v what is the kinetic energy of disk?I cannot solve the problem,
3
votes
2answers
1k views
Are there devices which convert thermal energy to electric energy?
Converting optical energy to electric energy is a huge business based on the photovoltaic effect. Is there an analogous effect for phonons? Are ther devices which convert phonon energy to electric ...
0
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1answer
173 views
Faraday's law and superconductivity
According to Faraday's law of induction, volts = -Number of coils in a solenoid * change in strength of magnet / change in time. This doesn't take into account distance or speed, only time. If amps = ...
0
votes
0answers
246 views
Error Analysis, Change in momentum, Kinetic Energy
If momentum of an object is increased by 10%,then its kinetic energy will be increased by?
Well, I don't need the solution logically by calculating the change in Kinetic Energy etc, but my question ...
0
votes
2answers
84 views
Painting wine botles
Yes, it's a physics related question. Read on.
I know from general knowledge that in order to produce a decent wine, you must keep it in a dark place. Therefore, from my knowledge of physics I guess ...
2
votes
1answer
134 views
Why don't cancelling wavefunctions for two different particles give zero total wavefunction?
Let $\left|a\right>=e^{i(kx-\omega t)}$， $\left|b\right>=-e^{i(kx-\omega t)}$ be two neutral particles in the 1D free space without any interaction. Then ...
4
votes
1answer
709 views
What is the relationship between Energy, Entropy, and Information?
What is the relationship between Energy, Entropy, and Information?
I read this - What Is Energy? Where did it come from? - and the top answer says that 'energy' is an abstract number that is a ...
26
votes
7answers
3k views
Is a hard drive heavier when it is full?
Browsing Quora, I saw the following question with contradicting answers.
For the highest voted answer:
The bits are represented by certain orientations of magnetic fields
which shouldn't have ...
2
votes
1answer
147 views
Man on treadmill and energy/mass conservation
Suppose we put a very obese man inside a large air tight isolated room with a treadmill and he runs on the treadmill for 24 hours and at the end of the day he sees his weight has come down (mostly ...
2
votes
2answers
86 views
Is there any correlation between the energy density fluctuations of two separate systems in a vacuum state?
I think the title says it all. What I am curious to find out is if there are any observable changes in the fluctuations of zero-point energy in a vacuum state system that are the consequence of ...
4
votes
4answers
5k views
What's the difference between Fermi Energy and Fermi Level?
I'm a bit confused about the difference between these two concepts. According to Wikipedia the Fermi energy and Fermi level are closely related concepts. From my understanding, the Fermi energy is the ...
0
votes
0answers
86 views
Is this a possible scenario for the teleportation of energy?
Ok, so I've been reading a paper (Here's the paper) published by a physicist named M. Hotta et al. recently and as far as I can tell with my limited understanding, the protocol for the teleportation ...
1
vote
2answers
168 views
Are the higher-order terms in the series for energy really negligible?
To show that energy in special relativity reduces to $E=m+mv^2/2$ for low velocities, if we make a Taylor expansion of $m\gamma$ around $v=0$ we get $$E=m+mv^2/2+3mv^4/8+\cdots$$ But why can we cutoff ...
1
vote
0answers
54 views
Energy efficiency of antimatter producion [duplicate]
Possible Duplicate:
Matter - Antimatter Reactory Practicality
Certain reactions in particle accelerators lead to production of antimatter, which can then be collected in noticeable ...
4
votes
3answers
627 views
Black holes and positive/negative-energy particles
I was reading Brian Greene's "Hidden Reality" and came to the part about Hawking Radiation. Quantum jitters that occur near the event horizon of a black hole, which create both positive-energy ...
0
votes
1answer
92 views
Do you think it’s possible to make a power plant of the described kind?
We are working on a science project and try to engineer a power plant of a new kind. It is called Air HES (air hydroelectric station). The idea is described on our website.
Do you think it is ...
3
votes
1answer
309 views
Wind Turbine Impact
OK, I'm not sure this is not a silly question, but here goes.
I've often wondered what the impact is of wind turbines on the weather. My question is, since wind turbines transform wind energy into ...
3
votes
1answer
131 views
Hamiltonians and Lagrangians, Euclidean and Hyperbolic: Are they related?
The Lagrangian of a system is the difference between its kinetic energy $T$ and potential energy $V$, and is relativistically invariant:
$L = T - V$
The Hamiltonian of the same system is the sum ...
1
vote
1answer
453 views
How are the CPU power and temperature caculated/estimated?
From Wikipedia
The power consumed by a CPU, is approximately proportional to CPU
frequency, and to the square of the CPU voltage: $$
P = C V^2 f $$ (where C is capacitance, f is ...
1
vote
0answers
144 views
Slackline Jump Tension
So a slackline is basically a bouncy tight rope.
I found a site that has a calculator for the tension of a static slackline
...
2
votes
2answers
704 views
Amount of energy required to hover.
I've noticed a motionless kingfisher over a lake looking for prey and wondered what amount of energy does a bird, weighing 0.15kg, require to hover for 15s?
1
vote
1answer
161 views
Why is “space-time” not fully explained as the observational effect of the casimir effect seen from a human perspective?
Simply stated the casimir effect can be observed bringing two plates together microscopically and in vaccum
Is this analogous to the observation of gravity?
Question: What is casimir effect?
...
1
vote
3answers
108 views
Carrying water on person, or on the frame when bicycling
So, the question is as follows:
What is the difference in work exerted by the rider in the two following scenarios?
a) Rider + bike. Water carried in a holder on the frame
b) Rider + bike. Water ...
2
votes
1answer
102 views
How is/do they plan on having fusion energy collected at the National Ignition Facility?
I was just watching a program on television showing how the method they use at the National Ignition Facility to attempt to achieve fusion is to fire extremely powerful lasers at a small pellet of ...
0
votes
2answers
99 views
Calculating kinetic energy?
Would this be a valid equation to calculate kinetic energy created from a drop from a height:
$$E_{kinetic} ~=~ v_{vertical}tmg$$
Velocity multiplied by time gives distance. Distance multiplied by ...
0
votes
2answers
89 views
Does using batteries in a series raise the overall Wh's of the batteries used? Why/Why Not?
If one has 2 batteries of 6 Volts each with 500 mAh each, then separately the batteries should provide 6 Volts * 500 mAh = 3 Wh each or 6 Wh total. However would it be the case that if someone where ...
0
votes
2answers
354 views
From knowing just the change in kinetic energy, can we find the friction force and engine power?
I understand this topic well enough to get all the task done because they aren't very creative. But for my exam I think I should have this clear.
During the acceleration the force from the engine is ...
0
votes
1answer
130 views
Decay of particle (for example $\pi^+$); Find energy
I don't understand how to solve this:
A $\pi^+$ decays into a muon and neutrino. Find the pion's energy if
max $E_\nu$ / min $E_\nu$ = 100/1;
$m_\nu = 0$
$m_\pi*c^2 = 140\text{ peta-eV}$
1
vote
1answer
118 views
Is energy “destroyed” when walking?
Conservation of energy states energy can't be destroyed, but isn't energy used up when walking in a straight line? If your not walking up a slope, kinetic energy isn't converted to gravitational ...
3
votes
1answer
333 views
I have a slight problem understanding the concept of “work”?
What I understand is that work is not the same as a car using gas or a crane lifting a car high up into the air. Let's use the crane as an example. And let me write out a few lines from the book.
...
0
votes
1answer
95 views
Is it safe for astronaut to do this “dangerous” movement?
So, if the astronaut is working outside the space station in thew space, could he not tie himself onto the space station and if he is going further away of the space station, i think he could just ...
2
votes
2answers
426 views
What's the relationship between an object's color and it's energy?
All else held equal, which has more energy: a violet-painted teacup or a red-painted teacup?
I know that violet light has more energy than red light, but does this mean that the inverse holds true ...
1
vote
1answer
98 views
Could ions emitted by an ion thruster represent any realistic danger?
As ion thurster designs improve, the ions emitted could have a velocity (relative to the spacecraft) of well above 10^5 or even 10^6 m/s.
It the likelihood of any such ions ever hitting a human ...
2
votes
1answer
329 views
What does the Fermi Energy really signify in a Semiconductor?
In understanding the behavior of semiconductors, I'm coming across a description of the Fermi Energy here and at Wikipedia's page (Fermi Energy, Fermi Level). If I understand correctly, the Fermi ...
