All Questions

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At time t=o a body is thrown vertically upward with a velocity u at time t=t [on hold]

At time t=o a body is thrown vertically upward with a velocity u at time t=t another body is thrown with same velocity u . when that two body will meet together ?
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What would the rainbow look like if we could see the full EM spectrum? [duplicate]

Would the rainbow look different if we could see the full EM spectrum (or at least a lot more of it)? Would the width of a rainbow be bigger and would all wave lengths of light be in a rainbow?
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How to write the Lagrangian for a body that exhibits gravitation?

Can anyone tell me how one actually goes about writing the Lagrangian for a mass that exhibits gravity? If I wanted to write the Lagrangian for, say, a spherical mass in space that curves the ...
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QED - Some problems with reflection from surfaces - diffuse, specular, IOR [on hold]

I've been reading about Quantum electrodynamics. There are a couple of effects that I see on objects, regarding reflections, that I cannot translate to the things that I did understand from this ...
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Thermodynamic process Question [on hold]

A 3.1-mole sample of an ideal gas is gently heated at constant temperature 290 K. The gas expands to 1.5 times its initial volume as its pressure decreases. What is the change in the internal energy ...
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problems on power, force and velocity [on hold]

A car of 1200kg is moving along a horizontal road, the engine of the car is working at a constant power of 24kilowatts. The frictional resistant to motion has a magnitude of 400N. When the speed of ...
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Resistors and dependent voltage sources

why not $i(2\;kΩ)=15\;mA$ and $i(5\;kΩ)=4\;mA$?
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Why New Zealand/cold countries has volcanoes? [migrated]

I understand that volcanoes are caused by the heat that causes high intense pressure inside the earth surface. This intense pressure gets released and causes magna which becomes hot lava to float out ...
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Gauss's Law for slabs

When you have a slab with thickness $t$ and infinite in other two directions , why $E \cdot A$ (flux) is zero in z direction ( shown in figure ) Problem 57 in the picture
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Why does mechanical energy have to equal zero to find escape velocity?

A object orbiting the earth has total mechanical energy equal to \begin{align*} E^{mech} = \frac{1}{2} m v^2 - \frac{GMm}{r} \end{align*} with $M$ the mass of the earth and $r$ the distance. My course ...
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Momentum distribution function for a particle in a 1D box

In these notes on statistical thermodynamics (pp. 62), I encountered this [topic: particle in a 1D box]: We shall adopt the initial condition that the probability distribution function has the ...
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Does Godel's incompleteness theorem deny theory of everything? [duplicate]

Ironically, Hawking's movie is named "Theory of Everything" when in fact he denied TOE based on Godel's incompleteness theorem Some people will be very disappointed if there is not an ultimate ...
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Why the whole wire moves when lorentz force acts?

We know that magnitute of lorentz force is directly proportional to the current in the current carrying wire. But since the force is acting on the charges,shouldn't they get exited or thrown out when ...
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How is the diameter of a nucleus measured? [duplicate]

From what i know, some statistical analysis is utilized in doing so. First, you take a thin slab of material, then fire particles which will reflect off the nuclei of the atoms in the material. The ...
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Why not take in account that magnetic dipole moment of particles is responsible for the magnetic field of accelerated particles?

The magnetic field of permanent magnets is explained by the alignment of the magnetic dipole moments of unpaired electrons (see John Rennie's answer to the question Why is there a magnetic field ...
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How does electromagnetic radiation get absorbed by an object (like a black body) in the classical regime? In the classical picture, electromagnetic radiation is produced by the movement of charges, ...
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Plane wave expansion of cylindrical functions:Summation of the Hankel functions

I understand that; in cylindrical coordinates, the basic solutions of the Helmholtz equation are of the form Hankel function of integer order times a complex exponential term ...
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Place one falls at after jumping off a building?

So a man is standing atop a tall building. The height of the building is not comparable to the radius of the Earth. Neglect atmosphere and revolution of the Earth. Let's say the building disappears. ...
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Dpss laser efficency calculation [on hold]

What is the efficiency of 532nm and 473nm Dpss laser modules? i know that is depends on so many factors,but in general calculation for a good quality Dpss modules.
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Why intensity of light(wave) is proportional to the square of its amplitude?

I am confused, Classical wave theory says that Intensity of the light(wave) is the proportional to square of the amplitude. How intensity is proportional to the square of the amplitude?
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How it is predicted, that a moving charge has to have a magnetic field?

This question appears after this comment: Even electric charges without intrinsic magnetic dipoles moments produce magnetic fields when they move. My respons: All electric charges (electron, ...
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Determining actual dimensions of an object from it's image [on hold]

I have to make an ios app that predicts the actual size (height, waist, chest etc) of a person based on his photo and then suggest clothes of that size. I just want ideas as to how the actual ...
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What are the dimensions of the stress energy tensor in relativity? [duplicate]

Can anyone tell me what the dimension of the stress energy tensor is? Also, if it represents energy density, will calling it kinetic or potential energy be appropriate?
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Change of direction in physics when an object in motion stops

Consider an object moving with an acceleration $a = -1 \text{m/s}^2$ starting with speed $v(0) = 4 \text{m/s}$ towards east and stopped after 4 seconds. (There are no friction.) After 4 seconds, the ...
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Relativistic deceleration and energy

It's common knowledge that due to relativistic effects, accelerating from 0.8c to 0.9c takes a lot more energy than accelerating from 0.1c to 0.2c. However, what's the case with deceleration? Does it ...
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If a super massive black hole captures a very small black hole, would the smaller black hole be immune to spaghettification?

I think to answer this question we would have to fully understand the nature of black holes. It seems to me that the smaller black hole could have a lower density than the larger one. In this case the ...
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Does stopping the same bike and rider at the same velocity with the front brake require less energy than the back brake?

It's the same body made by the rider and the bike moving at the same speed. So, even though braking on the front/back alters the normal forces on the opposite wheels thus creating more friction with ...
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relations opf space-time to gravitation as an evolutionary process [on hold]

just thoughts - 1 -gravity - could it be that it is not a fundamental force after all - could it be that it evolved after the big bang? space time was evolving and things [lets call them string but ...
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Capturing kinetic energy of air molecules [on hold]

How small a hole we can make on a 1mm thick metal plate? Can we make a hole slightly bigger than the diameter of the air molecule? If possible, can we make a small one way 'turnstile' inside the hole ...
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How can I understand Anderson's work “More Is Different”? [on hold]

Recently, I am reading P. W. Anderson's famous paper "More is different". I know it is a masterpiece, and many people have their thinking on it. Is there anyone can tell me something about it? ...
317 views

Why do we ignore rotational energy in monatomic gases? [duplicate]

I understand that the average energy of each degree of freedom in a thermodynamic system is $\frac12kT$. And so, for an ideal monatomic gas, there are three degrees of freedom associated with the ...
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Centrifugal force on objects rotating around Earth

Suppose two objects travel around the equator on Earth at the same speed, $v$, in opposite directions, where the speed $v$ is measured relative to the Earth's surface. Will they experience different ...
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What does it mean by saying the generators of translations transform as vectors under the Lorentz Group?

The commutator of generators of Lorentz transformation and translation is as follow: $$[M^{\mu\nu},P^\sigma]=i(P^\mu\eta^{\nu\sigma}-P^\nu\eta^{\mu\sigma} )$$ Then from this we usually say that the ...
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Symmetry considerations in Plane Poiseuille Flow

I'm taking a first course on fluid dynamics, and I have this (sort of) conceptual question that's been nagging me for a moment now. I can completely follow the mathematics behind the derivation of the ...
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Understanding incompressibility in continuum plasticity

I am a beginner in continuum plasticity and wondering physical meaning of incompressibility in continuum plasticity. Referring to MIT OCW link the consequence of incompressibility condition is (eq ...
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Why is $F=-\nabla V$?

I came across this equation $F=-\nabla V$ where $V$ is gravitational potential. I do understand that $F(r)=-\frac{dV}{dr}$. Hence does this mean the nabla operator in this case means derivative? ...
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Derive frequency given potential using Newton's laws

A mass with mass $m$ has a potential energy function $U(x)$ and I'm wondering how you would find the frequency of small oscillations about equilibrium points using Newton's laws. I started by finding ...
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Find an expression for S(T,x) from tension and specific heat

I'm working on a problem from a Statistical Mechanics lecture series online, and on the homework, I hit a bump in this problem. Here is the problem set, and I'm asking about #1.c. Short version, we ...
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Why, when and where is Gauss's law applicable?

Why is it said that Gauss's Law is mainly applicable for symmetric surfaces/bodies? Why not for asymmetric surfaces? I want a logical explanation! BTW my teacher said that Gauss's law is ...
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Constructing an equation of motion [on hold]

I have the following problem. Two particles initially located at $(0,0)$ and $(-1,0)$ start moving with constant speed ($v_b$ and $v_c$, respectively) towards $(0,1)$ such that at any time $t$ the ...
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Why we see a distant object more closer from us with a telescope?

The side magnification in the image obtained by a telescope its always less than 1, then, Why we see a distant object more closer from us?
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How do I calculate the change in water temperature as a function of depth?

Let's say I have ground water at a depth of $3000m$ at $50^{o}C$. If I now pump this water up to the surface, the water pressure decreases from the $\pm 300 atm$ at that depth to $1 atm$ at the ...
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Why does a wind turbine have only three blades? [duplicate]

Why not four or five or even more? Intuitively, the more leaves the more power. So, what is the reason?
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Green's function for the Klein-Gordon equation diverging?

I'm trying to work out the propagator for the free scalar field theory (i.e., the Green's function for the Klein-Gordon equation). On pages 23 and 24 of Zee's Quantum Field Theory in a Nutshell (you ...
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Redefinitions of Lagrangians using EOM

I am trying to understand an statement of this paper. In section 2 this Lagrangian is introduced ...
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What is time and time dilation? [on hold]

What is time? If it is nothing and just our understanding of the change then why does time dilation occur? If time is relative I think that time dilation shouldn't be possible. I just can't ...
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Light / TEM wave in a hollow waveguide

I'm cramming for my EMF exam, and a question came up: Light in free space is an example for a TEM wave, isn't it? (Maybe thats already my mistake) And we learned that in a hollow waveguide only TE ...
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Do moving charges produce magnetic fields?

As I understand it, a moving charge produces a magnetic field. Now it may be that I have have a misunderstanding here and if so I need to have the proper understanding of this. So if I do have a ...