-4
votes
0answers
24 views

About one dimensional motion [on hold]

A particle moves in a straight line and its position x at time t is given by x^2 = 2+t. Its acceleration is given by -2/x^3 -1/4x^3 -1/4x^2 1/x^2
0
votes
0answers
13 views

Color of cementite

I have a question about micrograph of steel. In eutectoid steel, the pearlite exists as grains, within each colony the layers are oriented in essentially the same direction, which varies from one ...
0
votes
0answers
32 views

Can neutrinos really travel faster than the speed of light? [duplicate]

A few years ago scientists found that neutrinos were going faster than the speed of light. Then they found some problem with the calculations. I read an article that was made this year about faster ...
1
vote
0answers
19 views

Equations of motion for controlled/driven classical systems? Does D'Alembert's principle apply?

I'm puzzled about how to derive the equations of motion for certain classical systems where some entity is controlling some of the DOFs. For example, consider a double-pendulum, with lengths $l_1$ ...
2
votes
0answers
65 views

Construction of a spin chain Hamiltonian invariant under a finite subgroup of SO(3)

I would like to construct a 2-local Hamiltonian that acts on a 1D spin chain where each spin transforms as the 3D irrep of $A_4$ which is a subgroup of $SO(3)$. I know that an $SO(3)$ invariant ...
3
votes
1answer
50 views

How come these 3d glasses don't show a difference between horizontal and vertical?

I thought that modern 3d glasses work by having one lens filter horizontally polarized light, and the other filter vertically polarized light. However, I found this pair of 3d glasses at my parents' ...
0
votes
0answers
37 views

Is there an efficiency-optimizing layout of items in a refrigerator? [on hold]

Is there some optimal layout of items, or types of items (characterized by size, shape, density, solid/liquid, etc) that will allow a common household refrigerator to function with optimal energy ...
0
votes
0answers
66 views

Classical probability explanation for quantum non-locality and Bell's inequality? [on hold]

The question is whether this solution is true or false, and if there is an error, please point what is it and where is it. Classical probability with local causality solution, just like tossing two ...
1
vote
1answer
53 views

$\dot \omega $ when momentum is conserved

If momentum is conserved when there is no externel force, why is there an acceleration when a momentum parameter is changed (inertia)? How does it accelerate with no external force? For example ...
-2
votes
0answers
28 views

Wondering what textbook is this problem from? [on hold]

Wondering from what textbook is this problem for?
4
votes
1answer
87 views

Is gauge connection unique?

In QFT, given a gauge group and matter field, is the form of the gauge field unique? In other words, given a principal G-bundle and its associated vector bundle, is the construction of the principle ...
0
votes
1answer
36 views

Grand partition function of gas of non-interacting spin-1 bosons in magnetic field

Consider a gas of non-interacting spin 1 bosons in a uniform B field, each subject to a Hamiltonian of the form: $ H(\vec{p},s_z) = \frac{p^2}{2m} - \mu_0 s_z B$ where $s_z$ can take the three ...
0
votes
1answer
56 views

Wavefunctions and Quark Confinement

While I have a decent knowledge of general relativity (and, of course, classical mechanics), I am quite a novice when it comes to quantum mechanics, so I apologize if this is a rather basic question. ...
0
votes
1answer
31 views

When the magnetic force is perpendicular to the velocity what will be affected on a charge? [on hold]

I guess it can also be stated as a two part question. Is the velocity of a charge always perpendicular to the magnetic force, and when the magnetic force is perpendicular to the velocity what is ...
0
votes
2answers
34 views

Resolution of the Eye-Light Rays and Diffraction

Please look at the problem. The problem is solved for me. However, I don't understand why the angle alpha is considered to stay constant when the rays go through the lens. The ray along the distance s ...
0
votes
1answer
24 views

Magnetic force and relative frame

The magnetic field for to a moving charge depend on its velocity (Biot Savart's law). My question is that is it then not frame dependent? If it is, it means if a man is walking and other is standing ...
0
votes
3answers
30 views

Current in purely LR DC circuit at t=0

I was told by my professor that the current in a purely LR Circuit with at initial state (JUST after closing the switch) is zero. Can you please help me understand why it that so?
1
vote
1answer
59 views

If the mass of an object or system is a measure of its energy content, multiplied by speed of light squared…?

If the mass of an object or system is a measure of its energy content, multiplied by speed of light squared, does it mean that the total potential energy of the rest mass of object or entire system ...
0
votes
1answer
54 views

Massive ropes and tension

Consider the diagram bellow, a massive string hanging in equilibrium My question is this: Can we take any 2 random point on the rope, say A and B and then use $\sum F=0$ on the rope between them: ...
0
votes
3answers
35 views

Doppler effect- will frequency continually decrease?

My problems: I know that when a person is moving away, the perceived frequency will be lower than the frequency of the source. However, in the question, if the person is moving away, the ...
-3
votes
0answers
24 views

Find out angle of a projectile [on hold]

For a projectile launched from a point on horizontal ground, the speed when it is at the greatest height is 25−−√ times the speed when it is at half of its greatest height. Determine the angle of ...
2
votes
2answers
55 views

Advanced Molten Salt Reactor - Is the concept of designing a reactor that uses spent nuclear fuel to generate power technically feasible?

I was going through the concept of designing a Nuclear Reactor that uses Spent Nuclear Fuel(SNF) to generate power as proposed by Transatomic Power . ...
3
votes
1answer
26 views

Lifetime of undiscovered element and its calculation

Reading about nuclear models, nuclear physics and the mythical ``stability island'' I just wondered about the next question: How can the lifetime of any undiscovered superheavy element be calculated ...
0
votes
1answer
22 views

What is the work done below proportional to? [on hold]

A raindrop falls from a certain height to the ground, with a terminal velocity u. The viscous force is F = 6*3.14*n*r*v, where n is the coefficient of viscosity, r is the radius of the raindrop, and v ...
3
votes
3answers
55 views

Ampere's law and external currents

In Ampere's law the current outside the curve taken is not included in the expression. Does this mean that only the currents crossing the area bounded by the curve taken contribute to the magnetic ...
4
votes
4answers
112 views

What is the intuition behind the Lorentz factor from Special Relativity

Time Dilation = $1/\sqrt{ 1-v^2/c^2}$ but why? How do you get to that conclusion? I know you use Pythagoras'theorem and my current understand goes like this: $$vt^2+ct^2=cT^2$$ then you take the ...
0
votes
0answers
39 views

Jacobian for Kronecker delta

I was revising on a bit of tensor calculus, when I stumbled upon this: $$\delta^i_j = \frac{\partial y^i}{\partial x^\alpha} \frac{\partial x^\alpha}{\partial y^j}$$ And the next statement reads, ...
0
votes
0answers
35 views

HOW CAN WE get THE ELECTRIC CHARGES FROM EARTH?explain it [on hold]

A question is distrubing my concepts which is that: CAN WE GET ELECTRIC CHARGES FROM EARTH OR FROM EVERYTHING?if we can,so what procedure would be?
0
votes
2answers
81 views

What to do when you are sitting in a closed room without any fan or AC

I suffered this today, when the solar panels of our college stopped to work. Imagine a situation in which you are sitting in a botany lecture conducted by a 73 year old man, who cannot speak loud and ...
0
votes
1answer
19 views

Is average air temperature related to near shore water temperature? [on hold]

Basically my wife booked to go on a beach based holiday but cloudy and only warm conditions are predicted for the area- does that mean the water is likely to not warm?- we are sensitive to cold. Its ...
0
votes
1answer
19 views

Conducting sphere with a cavity

I have a conducting sphere which has a cavity in it. The cavity is not at the center of the sphere. If a charge $+q$ is placed inside the cavity (with the sphere remaining neutral as a whole), what ...
1
vote
0answers
24 views

Similarity in two events from Dynamics point of view [on hold]

What is similar from dynamic point of view between book lying stationary on horizontal table and rain drop falling down with constant speed? I can find two similarities Force acting on them is ...
4
votes
3answers
73 views

What if all the electrons leave a metal?

I was studying photoelectric effect. Then I thought that what will happen if all the electrons from a metal piece come out as photoelectrons by using a light source of particular frequency? Will the ...
0
votes
0answers
26 views

Why can microwave (in microwave oven) heat the food but wifi can't? [duplicate]

As far as i know, microwave (used in microwave oven) and wifi all operate on the same frequency, but why microwave can heat the foods while wifi wave can't?
5
votes
1answer
134 views

Why are D'Alembert's Principle and the Principle of Least Action Related?

Why do we get the same differential equations from both principles? Surely there is a fundamental connection between them? When written out, the two seem to have nothing in common. $$\sum _i ( ...
1
vote
2answers
61 views

Definition of derivative operator on a manifold

I'm hoping to understand the motivation for certain parts of the definition of a derivative operator $\nabla$ on a manifold $M$. In Wald's General Relativity, two clauses of the definition are: ...
0
votes
1answer
21 views

Single Photon emission from positronium in strong magnetic fields; how is momentum conserved?

I recently came across a paper (which I will not describe in detail, however, the authors examine the probability of positronium producing a single photon, while under the influence of a strong ...
1
vote
1answer
108 views
+100

Is the observable universe homeomorphic to $B^3$?

Is the observable universe homeomorphic to $B^3$? Where $$B^3=\{x\in \mathbb{R}^3 : |x|\leq 1 \}$$ Or is it even sensible to talk about space (rather than spacetime) as a 3 manifold?
3
votes
1answer
103 views

Wick Rotation in Curved space

So over time I have learned to do exhaustive searches before asking things here. Wick rotations are cool if you are trying to work in qft and make statements about the thermodynamics of some physical ...
0
votes
1answer
25 views

Why does a motor draw more current stopped or under load? [duplicate]

I have a small motor connected to DC source, and use the ampere meter to survey the current through the motor. While the motor is rotating, I hold the motor by hand so that it stop. I see the current ...
2
votes
4answers
93 views

What is the motivation for the definition of a manifold?

In Wald's General Relativity, an $n$-dimensional $C^{\infty}$ manifold $\mathit{M}$ is defined as a set, with subsets $\lbrace{O}_{\alpha}\rbrace$, which satisfies 3 properties. In particular, the ...
0
votes
2answers
79 views

why the force of earth on a object is different from the force of object on earth [on hold]

I have a doubt in gravitation lesson about masses and forces. I have a doubt in gravitation lesson about masses and forces.
5
votes
1answer
76 views

Is force a contravariant vector or a covariant vector (or either)?

I don't understand whether something physical, like velocity for example, has a single correct classification as either a contravariant vector or a covariant vector. I have seen texts indicate that ...
2
votes
0answers
50 views

Why is thermodynamic equilibrium not reached by the system during a thermodynamic irreversible process?

In reversible process,due to infinitesimal steps,the system remains in thermal equilibrium(why?) . But in irreversible process, thermal equilibrium does not exist. What is the cause for this ...
0
votes
0answers
35 views

Radio telescope alternative. Does a high resolution radio camera exists?

I'm looking for an alternative to a radio telescope. Does a high resolution radio camera exists?
1
vote
3answers
35 views

How does Ohm's law apply to superconductors?

As radio amateurs we've all learned the various relationships of power, voltage, current and resistance as expressed in Ohm's Law. My question relates to the following simple circuit showing an ideal ...
0
votes
0answers
23 views

Examples of projection of angular velocity

I am looking for examples where the projection of angular velocity vector onto a different axis, has some interesting physical meaning in day-to-day contexts. For example, if a gramophone turntable ...
0
votes
0answers
16 views

what would be the requirement to convert water into electrical form [on hold]

I am wondering if it is possible to convert water into electrical form, as both have electrons and other chemical properties.
5
votes
2answers
126 views

Which electromagnetic radiation is faster in water, microwaves or light?

Well I've been asked this question, but I haven't been able to come with an answer yet using books and some web searches. The point is as the title says, to answer the question with the whole ...
6
votes
2answers
93 views

How can helicity be conserved but chirality not?

I read in a book that for $\beta$-decay the electrons have always been found to have an expectation value for their helicity of $h=-v/c$. Then ist is said in the book, that it follows from this ...

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