0
votes
1answer
24 views

Angular velocity in central force field

For motion in a central force field consider a rotating reference frame, which is characterized by the Euler angles $\alpha$, $\beta$, $\gamma$ associated with the rotation of the frame of Cartesian ...
2
votes
3answers
433 views

What is a body's momentum really equal to?

I know a body's momentum is equal to the product of its velocity and mass. But what kind of mass? Relativistic mass or rest mass?
1
vote
0answers
25 views

How to add together non-parallel rapidities?

How to add together non-parallel rapidities? The Lorentz transformation is essentially a hyperbolic rotation, which rotation can be described by a hyperbolic angle, which is called the rapidity. I ...
2
votes
1answer
29 views

Why does sunlight cause colors to fade?

If you leave something outside, its colors seem to inevitably fade or bleach due to exposure. Is this due to UV absorption? What sort of mechanism causes this - is it that man-made dyes deform on a ...
0
votes
1answer
47 views

How to calculate angular velocity given constant tangential acceleration? [on hold]

A car starts moving in a circle with a radius of $200 \text{ m}$. It has a constant tangential acceleration of $1{\text{m}\over {\text{s}}^{2}}$. a. What is the angular acceleration? b. What is the ...
1
vote
0answers
23 views

Maximum Power transmitted using General Relativity waves - cf Schwinger limit

In Electromagnetism, QED says that the linearity of Maxwell's equations comes to an end when field strengths approach the Schwinger limit. Its about 10^18 V/m. What is the corresponding formula for ...
0
votes
1answer
26 views

Does a correct application of the Lorentz force to find induced emf need resistance?

The emf between two points is defined as the work done per unit charge on the charge when moved (along a given and stated path) between those two points. To find the emf due to a magnetic field the ...
1
vote
1answer
16 views

Measured temperature (thermometre set to emissivity of 1) of smooth surface too high or to low?

We want to measure the temperature of a smooth flat surface with a thermometre based on absorption of thermal rays. The emissivity setting of the thermometre is set to 1 (same as a black surface), ...
0
votes
0answers
36 views

The “spooky action at a distance” and reference frame

It is often said that the measurement in EPR experiment is instant, as somehow described as "spooky action at a distance". However, the notation of equal time depends on reference frame, according to ...
2
votes
2answers
40 views

Spin State Energy Levels

When a spin-1/2 particle is placed in a magnetic field that is strong enough and varies slowly enough in space and time, it will become polarized and its spin will either align or anti-align with the ...
4
votes
1answer
51 views

General construction of equations of motion for free particles

I've got a question regarding the different Symmetrie-Lie-Groups of Newtonian Mechanics and special realtivity. Is there a canonical way to obtain the equations of motion for a free particle only by ...
1
vote
0answers
32 views

GR. Gauge fixing in 2-sphere [on hold]

I am working in GR with a tensor field ($A^\mu$) and a complex scalar ($\Psi=M e^{i\Theta}$). My geometry is $S^2$. I have my Lagrangian and my 2nd order equations. I want to fix the gauge, but I ...
2
votes
3answers
93 views

Distance traveled by a water jet

I helped my kid in a science fair project, where we punctured holes in a water bottle at various heights and then measured the distance traveled by the water jets before they hit the ground. The ...
4
votes
2answers
82 views

“Equidistant” spectra in quantum mechanics [duplicate]

In one-dimensional quantum mechanics, it seems that the only kind of potential able to produce an "equidistant" spectrum, i.e. with $E_{n+1}-E_{n}=\text{constant}$, is the harmonic oscillator. Why is ...
0
votes
2answers
50 views

How come the length of a wire does not affects on the circuit current?

Today we started learning about the electromagnetic induction. Out teacher gave us the following explanation: Suppose we have a conduction frame inside a magnetic field $\vec{B}$ going towards the ...
-1
votes
0answers
27 views

Need help with which books I should buy [duplicate]

I need some help with witch books i should read. I would like to study science, physics, quantum physcics, astrophysics and all other kind of physics. Hit me with the best books inside of thoes ...
0
votes
0answers
29 views

Free body driagram of box and plate with a friction force on a smooth surface

On a smooth surface we have a plate of 40 kg and on that plate a a box of 10 kg. Between the plate and the box there is a ...
0
votes
1answer
33 views

Newton's law for rigid bodies

Is newton's third law valid for rigid bodies? Say, if we have a bullet hit on a rod which is vertically placed on a rough floor. Friction is just sufficient sp that the rod rotates and does not ...
0
votes
0answers
35 views

How important is doing exercises in learning physics? [on hold]

I am a Chinese student who is currently studying physics at Nanjing university. And I just entered university a year ago. I am quite curious to know how you guys learn physics when you are in ...
1
vote
1answer
32 views

Why do nuclear bomb explosions create an array of visible electric discharges in the form of lightening in the upper atmosphere?

I've seen videos on the internet, showing nuclear bomb test explosions, and there appears to be a large amount of visible lightening discharging numerous times over the development of the mushroom ...
1
vote
0answers
62 views

Lagrangian, geodesics and relativity [on hold]

My background is in maths, but I have been studying some basic physics with occasional input from a friend who is studying for a physics PhD. Due to my background, I am keen to visualize things ...
1
vote
0answers
20 views

Saving energy/ petrol when drving [on hold]

Suppose you are driving on a straight road (with no traffic) at very low speed $v_o$, at one point the road goes downhill (A: grade 3%) and at the bottom (B) makes a V, going uphill again (C), up to ...
0
votes
2answers
99 views

Why superpositions? [on hold]

I've seen a lot of stuff on superpositions, namely the double slit experiment. And every video I watch, it tells me the same thing: It's amazing that when these particles are being observed they ...
0
votes
1answer
46 views

Has someone measured that in the far field of radio waves, the electric and magnetic field oscillate synchronously?

That in near field both fields oscillating 90° displaced is obvious since in antenna rod a lot of electrons will be accelerated and and this oscillation of electric field is escorted by alignment of ...
0
votes
1answer
28 views

Why does the Magnetic Flux Density B, saturates in a ferromagnetic material with increasing H?

I understand that the magnetization must saturate as more and more domains are aligned. But $B$ is still directly proportional to $H$, and hence it must increase linearly with $H$. But every book ...
2
votes
2answers
29 views

Resulting force when bending plywood

My sister and I are working on a thesis in interior design on a plywood chair similar to the picture, where the red part bends. We are trying to work out how much the plywood would push back when a ...
0
votes
1answer
27 views

Determine normal forces on tilted table [on hold]

A table with the mass m, the height a and the width b is resting on a tilted floor with the angle of rake $\alpha$. A block at A prevents the table from sliding. Determine the normal forces from the ...
1
vote
0answers
21 views

Gamma matrices in Decay Calculations [on hold]

I am trying to calculate the transition amplitude, $\lvert M^2\rvert$, for the process where a top quark (momentum p) decays to a bottom quark (momentum q) and a $W^+$ boson (momentum k). I am ...
1
vote
3answers
40 views

The speed of air rising through a heated tube

I would like to get an explanations of an observed physical phenomena. When a metal tube is placed vertically and heated and the air inside rises, the speed of the air moving through the tube ...
0
votes
1answer
67 views

Why is there zero point energy at absolute zero temperature? [on hold]

If we define the absolute zero as a temperature which there is no entropy in it so why should we have zero point energy?
0
votes
2answers
26 views

How can I calculate the partial trace for a combined state of a pair of two-level atoms to get a reduced state?

Let's say I have a combined state of a pair of two-level atoms, $A$ and $B$, given by the density matrix: $$ \rho = \frac{1}{2}\mid g_A, g_B \rangle \langle g_A, g_B\mid + \frac{1}{2} \mid g_A, e_B ...
0
votes
0answers
15 views

The angle of incidence of prism if emergent angle is 90°. Answer in terms of angle of prism and refractive index of prism [on hold]

A ray of light is incident at an angle of incidence i on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is n, ...
0
votes
3answers
26 views

Path followed by a free test charge in an electric field region represent the electric lines of forces?

As we know that if we put any free test charge in an electric field which is moving horizontally then it will experience an repulsive force and move in that direction so by that we can say that for ...
0
votes
0answers
16 views

How can a string “shield” a tear in a flop transition? Can our expanded dimensions tear?

I have read recently that in a process called flop transition in calabi yau dimensions space actually tears and is then somehow "fixed" to create a new shape of Calabi Yau dimension. If a string wraps ...
2
votes
2answers
149 views

Why do electric field lines start and end at 90 degree at the surface of a conductor? [duplicate]

There is one property of electric lines of forces which states that: Electric field lines start and end at 90 degree at the surface of the conductor. But why is that so? Is there any proof for ...
2
votes
1answer
49 views

Pinhole Camera Problem!

I was reading slides of a university course and in one of the slides it says 1 Eyes/cameras can’t have VERY small holes because that limits the amount of entering light 2 and diffracts/bends ...
0
votes
4answers
53 views

Negative density solutions of the Poisson's Equation for polytropic gas (aka Lane-Emden Equation)

Question: What does it mean by when we obtain negative density for specific region in space as a solution of Poisson's equations? I will explain the situation as detailed as possible, so that anyone ...
2
votes
2answers
40 views

Work done by frictional force on a sliding block

A block slides across a table horizontally with an initial velocity $V$. The frictional force $F$ brings it to rest after its Centre of Mass covers distance $S$. What is the work done by the ...
-15
votes
2answers
113 views

When will physics understand it is the 'dark mass' not the 'dark matter'? [on hold]

There is new thinking occurring in physics where 'dark matter' is considered to be incorrect. The new thinking is that mass fills 'empty' space. The mass which fill's 'empty' space is being referred ...
0
votes
1answer
37 views

What would be the Slater's determinant representation for an excited state?

Setup Introducing this spinorbital notation: \begin{align} \Psi_1=\chi_{(r1)}\alpha_{(\omega1)} = 1 \\ \Psi_1=\chi_{(r1)}\beta_{(\omega1)} = \bar{1} \end{align} and the Slater's determinant, for ...
2
votes
0answers
4 views

What would be the Slater's determinant of an excited state? [duplicate]

Setup Introducing this spinorbital notation: \begin{align} \Psi_1=\chi_{(r1)}\alpha_{(\omega1)} &= 1 \\ \Psi_1=\chi_{(r1)}\beta_{(\omega1)} &= \bar{1} \end{align} and the Slater's ...
0
votes
0answers
16 views

What is the connection between Bragg's condition with reduced EK diagram?

In my course notes the professor mentioned that there was some relationship between the Bragg's condition and the first Bernoulli zone of the reduced EK diagram. Specifically, the boundary before ...
0
votes
3answers
64 views

Levi-Civita symbol and Hermitian conjugate

When we take the Hermitian conjugate/dagger of an operator expression which contains a Levi-Civita symbol, do we need to transpose the Levi-Civita symbol? E.g., for the crossproduct ...
-2
votes
1answer
39 views

Free-Falling Object

How does the presence of air affect the rate at which a body falls? What is the rule for falling objects, when there is little or no air resistance?
0
votes
0answers
17 views

Constructing uniform mesh in reciprocal space?

This is a bit of a mental exercise for me to get comfortable with the math of reciprocal spaces since I am going to start doing some research that requires knowledge of reciprocal spaces. Let's say I ...
0
votes
0answers
25 views

RC Circuit Analysis

I want to correct three misunderstandings about the following RC circuit. 1) How does current move directly after switch S gets closed? Current runs through all three circuit components to begin ...
0
votes
0answers
28 views

Fermionic oscillator and Hurwitz zeta function

Good resources for calculating Partition function of the fermionic oscillator using the Hurwitz zeta function? I liked the way Nakahara explain this, but some parts are really tricky for me (e.g. the ...
1
vote
1answer
105 views

Questions about the formalism of Quantum Mechanics

I have to do a presentation on this. I'm not expected to do something really detailed, but I'm not understanding the mathematical formalism. I would like to receive general answers to these questions: ...
-5
votes
0answers
115 views

Did NASA mistakenly create a warp field? [on hold]

There is this new article that claims that NASA could have accidentally created a warp field. How likely is that to be true ?
0
votes
1answer
48 views

How do the electrons know the route?

I've learnt in classroom that the requirements for electrical current to flow in a circuit are as follows: there must be a closed conducting path between negative and positive terminals there must ...

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