# Tag Info

2

It is rather the other way around: our understanding of physics has enabled us to build GPS systems in the first place. It is correct however that GPS was direct confirmation of not only the theory of special relativity, but also of general relativity. Neglecting the time dilation from the difference in gravitational fields between the satellite's position ...

1

You understand that mechanical devices such as levers, gears, springs and pulleys all conserve energy. Do you think that some elaborate combination of such devices can violate conservation of energy? The same applies if magnets are included - we know that interactions between magnets conserve energy, so any combination of mechanical devices and magnets also ...

13

The proposal probably refers to terahertz (THz) imaging; THz is the band that is above microwave, but below infrared, between 100 um and 1 mm wavelength; often referred to as T-Rays. Because of their relatively long wavelength the T-Ray penetrates well into non-conductive materials, and is far, far below the ionization threshold. Thus it is safe to work ...

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Looking into this, the first thing that came up was a technology that used infrared light to determine the curvature of the pages of a book so it could be scanned non-destructively (in normal scanning, the pages need to be flat - before google's idea this was only possible with glass plates, which was inefficient, or dis-binding the book, which destroyed the ...

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First of All, I am confused by your question. Light travels at a constant speed in all reference frames. What is this "stationary observer in the Aether Field"? That doesnt make any sense to you or me. Forget about that. The experiment supports the non existence of a medium through which light moves in because of the null result. If you look back to ...

1

Yes, there is a duality and in the framework of quantum field theory (QFT) it is not even a contradiction at all. It seems pretty natural. All fields and particles are treated very similarly in the QFT language. Both are fields in space-time, so “waves”. There is a suble difference in the spin statistics, namely that fields corresponding to ordinary matter (...

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If you are measuring y at some value x, and both quantities have uncertainty, then in principle you should show the uncertainties on both axes. In some circumstances you might omit the x error bars. This would be the case if the y value depends on x such that $$\Delta y \gg |dy/dx| \Delta x,$$ where $dy/dx$ is your best estimate of the gradient of $y(x)$. ...

1

Hot water seems to freeze faster than cold water, known as the Mpemba effect $^{[1]}$. The effect was named after the Tanzanian student who in 1963 noticed that hot ice cream mix freezes faster than a cold one. The effect was first observed by Aristotle in the 4th century BC, then later Francis Bacon and René Descartes. Erasto Mpemba published a paper on ...

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This phenomenon you are describing is called the Mpemba effect after a Tanzanian student, Erasto Mpemba, who in 1963 noticed the temperature of ice cream affected how quickly it mix freezed, though the effect had been observed much earlier (the earliest known observation of this was by Aristotle in 4 B.C, though Aristotle probably didn't use ice cream). ...

0

If we know-and we are sure about-the relationship between y and x: If $y=f(x)$, you must propagate the uncertainty of $x$ to $y$. That is, since $y$ is analogous to $x$, then the uncertainty in $y$ is analogous to the uncertainty of $x$. So, you use a method that you can find in detail in Taylor's book "An Introduction to Error Analysis: The Study of ...

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The "formal law" that prevents this is called conservation of energy. The problem is that it costs energy to generate a current in the electromagnet - and more importantly, according to Lenz's law you will need to put in additional energy to maintain the flow of current when the coil moves towards the permanent magnet because the changing flux in the coil (...

1

There are mathematical ways of showing all this, but it is important to have intuition before starting to calculate. Here is my intuitive picture: The kinetic energy of the rolling cylinder has two components: The kinetic energy of its motion along the plane. The kinetic energy of its rotation about its own axis. The only source of kinetic energy is the ...

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Thank you for the update, WJ47. The slope of the blue tube looks very steep. Both the ruler/tube and the white cylinder (cellotape holder) look quite smooth, so I think there will be little friction, resulting in a mixture of rolling and sliding here. It is very difficult to predict how much of each. This is a rather 'messy' experiment, IMHO, difficult ...

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The answer to your 1st question is a trivial "Yes." If testing the material shows that stress is proportional to strain within the range of interest, then it is obvious that a linear model is appropriate. Why would you think otherwise? What other answer could be given? In your 2nd question, you are trying to apply strict mathematical criteria in the ...

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You will still have light on the other side. The eigenmodes of the fiber are complete set so any light will be happily decomposed. Light is still incoherent. In principle you could excite single mode.

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The effect is noticeable even here on Earth, and in fact it has been used to measure the mean density of the Earth in experiments such as the Schiehallion experiment. The principle is simple: take a pendulum. If there is no large-mass object nearby (such as a mountain), it will hang straight downward, pointing to the center of the planet. But if there is a ...

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I just add to above points which are mostly correct my two pennies. 1- the wire is loaded with a history of residue strains from the manufacturing and handling so the stiffness and elasticity of it is not homogenous lengthwise or even along cross-section. if you'd write the whiplash DE's in a finite element software it is not a linear differential equation ...

72

Your wire is not quite round (almost no wire is), and consequently it has a different vibration frequency along its principal axes1. You are exciting a mixture of the two modes of oscillation by displacing the wire along an axis that is not aligned with either of the principal axes. The subsequent motion, when analyzed along the axis of initial excitation, ...

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UPDATE : After looking again at the video, I agree that Floris' explanation seems to be correct and my explanation below is wrong. Slightly different frequencies of vibration in two perpendicular planes accounts more simply for a rotation which reverses one way then the other. Kinetic energy seems to decay constantly; it does not seem to be stored in an ...

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Is it possible that two photons move in parallel, on the same trajectory - having the same wavelength, but differ in phase? Photons are quantum mechanical entities/particles listed in the elementary particle table which is the basis of the standard model of particle physics. When measured individually, it just gives an (x,y,z,t) , by interacting with some ...

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Your question is short on details, so to answer your question I am assuming a particular configuration. Hope it helps with whatever your actual configuration is. A closed porous container consists of a gas at partial pressure $p_1$ which is less than partial pressure $p_2$ of that gas in the ambient. We shall assume that $p_2$ is constant and to further ...

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Get a microscope slide or equivalent thin piece of clear glass. Paint the central portion with india ink or spray with black paint. The coating should be thick enough to prevent the passage of light. Let dry. Using a razor blade and a thin straightedge, scratch a thin line through the paint across the slide (perpendicular to the long direction). As close as ...

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The equation you wrote is for steady state flow through a porous wall of thickness d. Q is the volumetric flow rate. Q/A is the so-called superficial velocity. The equation inherently assumes that the pressures on both sides of the wall are constant, and not varying with time. The only way that you would get an increase in pressure difference with time ...

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in order to obtain the wave nature of light you need to make your slits as close to each other as you possibly can as well as make the slits as thin as possible. The two slits/holes need to be VERY close to each other I applaud you for taking interest in experimental physics! Often times experimental physics is a matter of changing all the variables you ...

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The angle between maxima in the double-slit pattern is $$\theta \approx \frac\lambda d$$ for wavelength $\lambda$ and slit separation $d$. I wild-guess that the slits in your photograph are about 5 cm apart, so your diffraction peaks should be separated by $$\frac\lambda d = \frac{\rm 500\,nm}{\rm50\,mm} = 10^{-5}\rm\,radian$$ which is too small for you ...

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As an update on this old thread, the 2015 version of the Particle Data Group review on tests of conservation laws (the 2009 version of which was rightly pointed to by invisiblerhino) has an interesting update: The BABAR experiment has reported the first direct observation of $T$ violation in the $B$ system. The measured $T$-violating parameters in the ...

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Regularly spaced light and dark bands far from either anode suggests a simple matter of the electrons picking up the kinetic energy necessary to excite the neutral atoms, giving most of it up when they do so, and then re-accelerating down the tube. We would expect a couple of diagnostic features: The bands nearer the cathode to be more sharply defined ...

2

Use a Focault Pendulum, measure the rotation period of the plane of oscillation and compare it with the theoretical value $$T=\frac{24\, h}{|\sin\lambda|},$$ where $\lambda$ is the latitude. If the precession is clockwise you are in the northern hemisphere, otherwise you are in the southern hemisphere. No precession means you are at the equator line.

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The fine structure constant $\alpha\approx\frac1{137}$ appears in the Coulomb force between fundamental charges: $$\alpha\hbar c = e^2/4\pi\epsilon_0, \quad\text{so}\quad |E_\text{Coulomb}| = \frac{e^2}{4\pi\epsilon_0} \frac1r = \frac{\alpha\hbar c}{r}$$ Quantum electrodynamics is pretty well tested down into the radio frequencies, with techniques like ...

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Hawking radiation is a theoretical result from the analysis of quantum field theory in general relativistic, curved spacetime. This sort of semi-classical analysis, combining aspects quantum mechanics of with classical GR, is a stepping stone to a full theory of quantum gravity. The theoretical result does not prove that Hawking radiation exists. If ...

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I will first show a simple way to think of Hawking radiation and how we might indirectly observe it. If you have a particle on an accelerated frame it is within what is called a Rindler wedge. Below is a diagram of spacetime for an accelerated frame. We think of a particle in region I The hyperbolic lines are regions of constant radius from the $45$ degree ...

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OK..Imagine for a moment that your discussion is pushing a direction you haven't considered. Matter such as protons and neutrons being broken down into smaller particles…the space they take up even though their weight is the same is greater..a force as powerful as a black hole would be strong enough to accomplish this. In turn the increase in space taken ...

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The speed of light is invariable but the number or ratio of the frames of reference are variable as determined by the amount of gravity, the result of which is gravitational lensing.

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