# Tag Info

2

An incompressible liquid is never completely incompressible, more like quasi-incompressible. So when you apply considerable force $F$ on the piston, pressure will wise by say $\Delta p$:: $$\Delta p=\frac{F}{A},$$ where $A$ is the cross-section of the piston (and assuming constant $F$). But the liquid will have decreased slightly in volume by $\Delta V ... 1$p=\frac{1}{3}\rho$is the well-known equation of state of a photon gas. It may be derived by looking at the ultra-relativistic limit of the energy momentum tensor for a bunch of particles.$^1p=-\rho$follows from the fact that the energy momentum tensor of$\Lambda$-style dark energy is proportional to the metric. Thus, at a point and in the proper ... 2 You're right that the unit "megawatt" is abbreviated MW. However, as Aniket comments, watt itself means "energy per unit time", so saying that the power plant produces 60 MW per hour doesn't make sense. In your comment, you question whether MW is a "basic unit". I'm not exactly sure what you mean by this, but the SI unit of power is watt, so if you want to ... 1$\mathrm{Watt}$(or Joule per second or$\mathrm{J/s}$) is the SI unit of power. So megawatt is a valid unit of power (expressing power with order of magnitude$10^6$) and is used mainly in commercial statements. Definition: Power means the quantity of energy consumed or produced per unit time. So$\mathrm{MW/hr}$actually makes no sense since it ... 0 Notice, the unit of power is$~\mathrm{J/s}$or$~\mathrm{W(Watt)}$. The unit$~\mathrm{MW}$indicates the energy (in$~\mathrm{mega\ joules}$) produced by power-plant per unit time (in$~\mathrm{seconds}$) The unit$~\mathrm{60 \ MW\ per \ hour}$doesn't represent a physical quantity. 1 Expanding on what Couchyam said: To some extent, this is actually the definition of what it is to be a "particle." Intuitively, a particle should have some particular definite energy, and be stable enough that it can exist in its own right. These two requirements are linked by energy-time uncertainty. The natural "clock" to compare against when asking if ... -2 Energy can neither be created and nor be destoryed it can changes from one form to another form. For daily life example just when we do any work as for example just when we play a football and kick in the football and take our energ to football to kick it then energy is going into football and it can move from KINETIC ENERGY INTO POTENTIAL ENERGY 1 No it is separate issue to total internal reflection. The important thing here is frequency dependent emissivity of the materials. Very simply speaking, the absorber needs to have high emissivity in the optical and NIR region (so it strongly absorbs sunlight) and low emissivity in IR, so that the thermal energy is not radiated away. It is like a green ... 1 The formula that WhatRoughBeast uses is not correct. It should be $$KE = \left(\frac{1}{\sqrt{1-\left(\frac{v}{c}\right)^2}} - 1\right) mc^2 = \left(\frac{1}{\sqrt{1-0.22^2}} - 1\right) (22,000)(3\cdot10^8)^2 = 5\cdot10^{19} J$$ Your calculation wasn't far off since relativistic effects aren't very large at 22% of the speed of light, so$KE = ...

1

You've underestimated the effect, although your math is correct as far as it goes. At 22% of c, relativistic effects do rear their ugly heads, and the proper equation is $$KE = \frac{\frac{mv^2}{2}}{\sqrt{1-\frac{v^2}{c^2}}} = 7.6\times10^{19}\text{ J}$$ Divide by $63\times10^{12}$ and the ratio is 1,200,000 (1.2 million). And yes, this is an unreasonably ...

0

The question was "True or false. The greater the dampening of the system, the quicker it loses energy to its surroundings." ... I was wondering if there is a good example preferably with calculation to show me proof of this. A mass $m$ travels at speed $v_{initial}$ and suddenly reaches a surface where the friction coefficient is $\mu$. By writing the ...

2

If the WiFi antenna is emitting at 2.4 GHz, you could detect a slight improvement of the signal, but unless the door is solid and very thick, I doubt it will make much difference. If it is emitting at 5 GHz the improvement could be bigger, as the wavelength is reduced and the door appears "bigger" to the electromagnetic wave. Finally, if your antenna uses ...

0

For part (1.) think about this: just as the spring comes to rest momentarily all of the energy in this system is stored in potential energy of the spring itself. First find the spring constant $k$ using Hooke's law. From there you can find the potential energy stored in the spring. You then know that just as the mass comes in contact with the spring the ...

1

You can draw a schematic diagram to analyze it and suppose that elastic force is $F=-kx$ by Hooke's law and the gravity is $mg$.

1

A material of high specific heat, coupled with another material of high thermal conductivity, might just do the trick. I would suggest water (high specific heat) taken in a metal tank(high thermal conductivity). Though this can be the best option, scientifically(talking about efficiency), it might not be the same aesthetically

1

Its not that tough. You can work it out by using just two equations. But the one thing you should keep in mind is that when the comet is at the minimum distance from the sun, its velocity must be perpendicular to the radial vector (sun to comet). So the minimum distance is itself the minimum perpendicular distance used in the angular momentum formula at ...

0

What happens is not a transfer of kinetic energy from the weight to the pulley. Rather, the pulley accelerates slower and then reach a lower speed because part of the work done by gravity is directly transformed into rotational energy of the pulleys. Yes, both translational and rotational motion energy are forms of kinetic energy.

1

from the figure: liquid that cannot be compressed... so forget compression of springs. Molecularly, particles in a liquid have much less space to move around (short mean free paths) compared to particles in a gas. The result is that any applied pressure to these particles is instantaneously transferred through the fluid. The mechanism by which this happens ...

0

In the general case the frequency of a wave and its kinetic energy are not related. As you can derive from Energizer 777's answer one can increase the frequency and this time decrease the amplitude of the wave generator and you approximately need the same amount of energy to support the damping of the wave from dissipation processes. The point is that an ...

0

Work and kinetic energy are interchangeable, so they are the same, ie. they have the same units. Your work can give kinetic energy to a body and a body with kinetic energy can produce work.

1

The Newton unit is not a fundamental unit but consists of: $$\mathrm{[N]=[kg\cdot m/s^2]}$$ which you can convince yourself of from Newton's second law $F=ma$. Plug it into $\mathrm{[N\cdot m]}$ and you'll see.

0

Suppose the maximum angle of the pendulum to the vertical direction is $\theta$, where the pendulum has a zero-velocity. According to the conservation of mechanical energy, the total energy of the system, $E$, should be: $$E=mgl(1-\cos\theta )$$ If $\theta$ is small enough, we can expand $\cos\theta$ up to the second order: $$\cos(\theta)\approx ... 1 There are a fairly large number of replications of both the Nickel-Hydrogen variant and the original Fleischmann-Pons Palladium-Deuterium electrolytic cell variant. See this for a recent survey: https://www.academia.edu/17964553/Condensed_Matter_Nuclear_Science_October_2015 The results are becoming more mainstreamed (Wired, Forbes, Huffington Post), and thus ... 1 The acceleration of gravity is the weight of the object on the surface. If the structure, either of the object or the surface, is deformed by the weight, then part of the gravitational potential energy of the object will turn into kinetic energy of surface moleucles and therefore heat, and this will be shared between the object and the surface. In this ... -1 Checkout John Williamson's work, for example being discussed here: https://www.physicsforums.com/threads/is-the-electron-a-photon-with-toroidal-topology-what-is-that.614799/ He derives Maxwell's equations for the electron with the Lorenz transformation taken account for relativity. It's quite good IMHO; carrying on with the work that Dirac was doing with ... 0 With respect to current theory my answer may prove quite unpopular (down votes expected), so please take this answer with a grain of salt if you are still in school. Your approach in this 'thought experiment' that you propose is very much like some of my own research conclusions. In direct answer to your question, yes, General Relativity should require an ... 0 I) What does it exactly mean when we say that energy has moved from one body to another, what has physically been transferred? Contrary to the view expressed above by Mark H < http://physics.stackexchange.com/a/217505/76263 >, I think energy is a fundamental physical property and not just “an abstract [useful] mathematical quantity”. In fact, the ... 0 First two answers to your questions must have gave you some good understanding of Energy, Spectra & some history of early Quantum Mechanics. Please read them again before you read my analogy. I'm directly moving onto analogy without wasting "Space" & "Time". In Classical systems, the movement of energy is like an movement upwards on a Ramp. In ... -1 Mass is energy, not being able to go at the speed of light in a direction. If the photons creating the electrons and positrons are going at the speed of light in a tight loop as John Williamson describes in a half dozen papers, then it can't also go at the speed of light in the perpendicular direction. 0 Energy does not require force, as a moving object will have kinetic energy even if no force is acting on it. To give energy to an object is using work, so the second question is really asking if force requires work. The definition of work is the integral of the force function from the inital position to the final position. Even if there is a force, if the ... 1 Potential energy is the energy due to configuration of the system. If you keep three charges very, very far from each other, then the potential energy of the system is very effectively zero. But when you bring them close together to a specified coordinate, then the potential energy of the system increases from 0 to a positive value given by$$U= ...

0

Potential Energy is calculated of a system, ie, a system possesses potential energy and the capacity to do work with it. If you a raise a ball of weight mg to a height h above the surface of the earth, then the total potential energy of the ball will be PE = mgh as you have done work against the gravity of the earth and thus the ball possesses a certain PE. ...

1

There are different forms of energy. Energy can be converted from one form to another but cannot be destroyed. In this case the kinetic energy of the hammer is driving the nail into the wood which is breaking the molecular bonds in the wood fiber. The energy is converted to heat energy as a result of the breaking of the bonds and the friction of the nail in ...

0

we talk in General Relativity [...] about curvature of space and time At least (without implying strict separability) about curvature of spacetime; right. In this context it is however possible to distinguish "free (inertial, falling) motion" from "any other motion", The latter is accordingly said to be "due to (external) influence(s)", and its ("first ...

0

Well, in a sense any kind of hard surface is an electromagnetic shield. Why? Because the forces holding atoms together and pushing them apart are electromagnetic. For example, the reason you don't fall through the floor is because the atoms in the floor electrically repel the atoms in your shoes. This is an electromagnetic interaction! If you mean a ...

3

That's not quite how the brain works. Not a lot of mass actually moves, but the electrical impulses with which neurons communicate require the repetitive movement of electrical charge against differences in electrical potential, and that takes work. In fact, the human brain requires significant energy to do its job. Quoting from Appraising the brain's ...

-1

A body at rest in a gravitational field ((as standing on the surface of the earth) is the same as a body being accelerated. A free falling object is equivalent to not accelerating (The equivalency principal). The Accelerated one at rest would heat up. OK so maybe I didn't articulate that so well please let me try again. The equivalence principle states that ...

2

If the object is at rest it would imply that gravity transfer heat without an increase in potential energy, and there are no other forces that produce work. This would violate the conservation of energy. Regarding your comment "any contact forces imposed on an object will increase that object's heat energy": this is incorrect, friction only results in heat ...

0

One way is to connect the ignition to a high voltage (10kV) capacitor. Then the energy is: $$E = \int VI d t = \frac{CV^2}{2},$$ where $C$ is its capacitance and $V$ its voltage, assuming that you connected it and did the measurements so that energy losses are negligible.

1

A general wavefunction for a system can be expanded as a sum of the eigenfunctions, $\psi_i$: $$\Psi = a_0\psi_0 + a_1\psi_1 + a_2\psi_2 + \,...$$ The coefficients $a_i$ are calculated using: $$a_i = \langle\psi_i | \Psi\rangle$$ If you do a measurement just once you will get one of the eigenvalues $E_i$, and the probability of getting each ...

2

Potential energy is wrong. Even in Newtonian Mechanics it only works if the force is 1) purely a function of position and also 2) is conservative. Magnetic forces depend on velocity so they fail. And electric forces are not conservative if you aren't in statics. What you really have is kinetic energy and rest energy for the charged particle, some energy ...

1

Yes you can. You have to "walk" in such a way that you will exert a force that is perpendicular to the motion of the escalator. Of course that means you will accelerate toward the bottom of the elevator, at the same rate as if you were on a frictionless slope. You can still accend the elevator if your initial speed is high enough. (Please don't try ...

1

Don't forget about the rest energy, $E=mc^2$. Since a particle's intrinsic spin cannot be changed, it doesn't make sense to distinguish "intrinsic spin energy" $\frac12 I\omega^2$ (as you would compute for, say, a spinning flywheel) and the rest energy. A particle which is moving in an electric field will see a motional magnetic field. Charged particles ...

0

It is maybe because this quantity is dependent on the square of the velocity and on the mass of the body, meaning, two other quantites. Best way to get some feel for energy is to imagine, and maybe, perform, experiments with collision of bodys with different masses and velocities. So, for example, let the body that you are launching be of constant mass and ...

4

What is energy? I'm going to start by using a very basic understanding of energy (one suitable for a first year course): Energy is any property of an object or system to allows it to do work. Here "work" is used in the sense of force applied over a distance: $\mathrm{d}W = \vec{F} \cdot \mathrm{d}\vec{s}$. What kinds of properties would qualify this ...

Top 50 recent answers are included