All Questions

Filter by
Sorted by
Tagged with
0
votes
1answer
6 views

In case of banking of roads, why do we say that it is the STATIC friction which provides the centripetal acceleration?

My question is rather simple. Why do we say that is the static friction or to be more precise, the component of static friction which provides the centripetal force? The car is in motion. And static ...
0
votes
4answers
57 views

What is angular velocity in 3-dimensional space? (Revised)

If I'm not mistaken, there are analogies between the translational dynamics of a rigid body and the rotational dynamics of that body. For example, the position of a rigid body is analogous to the ...
1
vote
0answers
6 views

Are unstable particles created with an exact mass, or masses distributed in resonances?

I'm pretty comfortable with QFT, but this is a conceptual point I feel shaky on. For example, when creating Z bosons in a process like $e^+ e^- \rightarrow Z Z \rightarrow f^+ f^- f^+ f^-$, the Z ...
1
vote
1answer
36 views

Check that $\eta^{\mu\nu}T_{\mu\nu}=0$

I'm trying to solve a problem and I have some problems for that. The problem is to show that $\eta^{\mu\nu}T_{\mu\nu}=0$, where $\eta^{\mu\nu}$ is the Minkoswki metric: diag(1,-1,-1,-1), and $T_{\mu\...
0
votes
2answers
29 views

Do wormholes really allow us to travel back in time?

Theories surrounding wormhole based time travel are annoying me tonight... So the way time works is relative, right? The closer you are to the frame of reference, the faster time moves. So, if we use ...
1
vote
3answers
28 views

DO I have the correct idea of time dilation?

suppose that I send my twin away from the earth at 87% the speed of light. From the time dilation equation, since the twin is moving, the time interval between any 2 events, as measured by me, would ...
2
votes
5answers
76 views

How can a mass $m_1$ lift a heavier mass $m_2=2m_1$?

In below diagram, in what angle $\theta$ should we drop $m_1$ so that, right at the moment of dropping, $m_2$ would lift upwards? Assume $m_2=2m_1$. This is in my homework and I don't even understand ...
0
votes
0answers
11 views

Help deriving optical path

I have to derive the path of a light ray traveling in a stratified medium with linear variation of its refractive index. For context the first two exercises ask you to derive Snell's law using ...
1
vote
2answers
237 views

Why did the apple explode when spun very fast?

This new video from the slow-mo guys captures the explosion of an apple when it is rotated really fast (roughly $109$ rotations per second). But can someone explain me why did it cut into clear halves ...
0
votes
0answers
26 views

Why the force is inversly proportional to the square of distance? [duplicate]

Lesser the distance higher the force of attraction.but why it is the square of distance?And also the reason i guess for this force is the attraction force between atoms ( electrons of one atom and ...
3
votes
1answer
224 views

How does a heated lid in a thermal cycler prevent evaporation?

A thermal cycler is a chemistry lab device that increases or decreases the temperature of the material inside it. The lid of the device is heated to prevent condensation and evaporation of the mixture ...
0
votes
0answers
5 views

Fluid Mechanics Infinite Plate Assumption

What should be the correct definition for a flow between infinite parallel plates? If I have a very long rectangular channel with height H and width W, can I approximate the flow through the channel ...
-2
votes
2answers
30 views

What causes gravitational force?

I was thinking that the reason behind the gravitational force is the magma, but after studying Newtonian model of gravity I am confused. It says that there can be gravitational force of attraction ...
0
votes
2answers
206 views

Conducting cylinder by dielectric interface

To help me with a project I'm working on, I attempted to solve what I thought was an easy problem. There is an infinite, conducting cylinder of radius $R$ at some potential $V$, located a distance $b$ ...
0
votes
2answers
42 views

Regarding Michelson's interferometer

In Michelson's Interferometer (1881 experiment), even though the arm length for both the perpendicular arms was taken as the same (say $L$) and a compensatory plate was used to removed optical path ...
0
votes
1answer
21 views

Difference between particle rapidity and space-time rapidity

I have seen a lot of posts asking about the difference between the rapidity $y$ and the pseudorapidity $\eta$, and I understand it well enough (at least in the context of heavy-ion collisions). They'...
1
vote
0answers
31 views

Proper definition of Berry curvature

I see at least two different definitions of Berry curvature in literature. One is given at Wikipedia $$ \Omega_n = i\sum_{n\ne n'}\frac{ \langle n|\partial_{k_x} H|n'\rangle \langle n'|\partial_{k_y} ...
1
vote
2answers
61 views

If you keep the center of gravity of two objects on each other would you never be able to separate them?

To find the attractions between planets and stuff like that, you use the center of gravity/mass to apply to Newton's equation. So even if those planets collided into each other, you could separate ...
1
vote
2answers
412 views

Is there a formula to calculate the deviated angle of a ray passing through a prism?

I'm assuming the angle of incidence to be the number of degrees from a perpendicular line on the side of a prism the ray starts passing through... I'm trying to figure out the angle the ray would be ...
7
votes
3answers
329 views

Are Van Der Waals Forces the Similar to Van der Waal Equation?

In a physics class, I learned about Van Der Waals forces that allow geckos to stick. Do they have any relation to the Van Der Waals Equation relating gas pressure to temperature and volume?
-2
votes
1answer
50 views

How can we apply a sine curve in Newton’s law of cooling?

Please anyone would it be possible to explain the process with detail of example 2 in the website I will link which measures Newton’s law of cooling with an uncertainty in temperature. Please I really ...
0
votes
1answer
334 views

Calculating magnetic strength required to hold an objects weight + wind speed?

Note: I'm a bit new to this subject, so I'm looking for some general answers, ballparks, and direction to continue my research. Scenario: I have three electromagnets capable of X amount of holding ...
0
votes
0answers
16 views

Absorption spectrum of Hydrogen

why lines of Lyman series are absent in absorption spectrum of hydrogen ?
2
votes
2answers
69 views

Problem regarding the definition of spinor

I am trying to build a simple understanding of what a spinor is, in doing so I have stumbled across two different definitions of spinor: First definition: If $|\psi\rangle$ is a generic state of a ...
0
votes
1answer
11 views

Details about the delocalization of electron in metal

Electrons in conduction band of metal is delocalized. (1) How much is it delocalized? Will it be delocalized to the whole metal sample, or will it's wave function only cover a few/a dozen atoms nearby?...
0
votes
1answer
128 views

Solving the $CP^N$ model in large $N$ limit

I have trouble filling in the essential step of solving the $CP^N$ model in large $N$ limit, described on Page 84 to 86 of Michael Dine's Supersymmetry and String Theory. The Lagrangian is given by $$...
0
votes
0answers
12 views

Question about Laughlin's pump

In Laughlin's gauge argument for integer quantum Hall effect, we adiabatically thread flux from $0$ to $\Phi_0$ (the flux quantum) into the Corbino ring Hall bar, and the system is left invariant and ...
7
votes
2answers
886 views

Why Are Normal Shock Waves Unstable in a Converging Channel?

While learning about shock waves in an introductory Gas Dynamics course, it was revealed that normal shocks are unstable if formed in a converging channel. Even if the local conditions ostensibly ...
0
votes
0answers
7 views

Microscopic surface charge distribution on a metal ball

On a metal ball with perfectly smooth surface with negative charge on it, the charge will be distributed evenly on the surface, but microscopically where exactly will the charge reside? Although the ...
5
votes
1answer
141 views

Hitting bottom of an axe to seat the axe head

I have been thinking about a certain step in hafting an axe which I can't seem to explain physically. As a reference, I've found a forestry manual which explains the process, in case my explanation is ...
0
votes
1answer
45 views

Rocking a bottle back and forth - What physics systems are at work?

I want to understand the physics that occur during the attempt at tipping over a bottle / rocking a bottle back and forth. I am expecting that: when the finger pushes the bottle for a tiny moment, it ...
1
vote
1answer
35 views

Probability current and Travelling waves

Consider a travelling wave $\Psi(x,t) = A e^{i(kx-\frac{\hbar k^2}{2 m})}$ According to the formula for probability current $J = \frac{\hbar}{m} Im( \Psi^*\frac{\partial\Psi}{\partial x})$, the ...
0
votes
1answer
37 views

What is the best way to solve an half spin particle exercise?

This question is strongly related to this other question regarding the definition of spinor. Let's take for example the following exercise: Given a particle with mass $m$ and spin $1/2$, described by ...
0
votes
0answers
6 views

Dielectric constant of neutron ball and the behavior of EM wave in it

When plane EM wave go thourgh ordinary dielectric, the small separation of atomic nuclei and the electron (i.e. dielectric polarization) will result in the dielectric constant and the slow down of the ...
2
votes
2answers
270 views

How can I determinate the air flow coming out of a pressure tank?

I have a trouble with a simple question (I think). Well, if a have a tank full of compressible air at a pressure of for example 6 bar and a valve with a hole of 8 mm diameter, how can I know the ...
0
votes
0answers
6 views

When will iridescence only happen when seen through a mirror-like surface?

The phenomenon is: A semi-opaque semi-rigid plastic sheet covers a window, if you see the sheet directly from any direction, there is no iridescence on the sheet. But if you see the sheet through a ...
0
votes
0answers
48 views

Lagrangian mechanics of elastic collisions

How does Lagrangian mechanics apply to the elastic collision of particles?
0
votes
0answers
13 views

Proof/Derivation that a normal force applied to a rigid body object causes a torque?

I saw this answer here but didn't understand it. If someone could provide a simpler proof starting from newton's second law F = ma and only using his 3 laws that would be helpful (only because I don't ...
1
vote
0answers
31 views

Trace of the log of a matrix

When Zee computes the Grassmann path integral in Section II.5 of his QFT book, he uses an algebraic step I can't follow. I follow this part: \begin{align} \text{Tr}\ln\!\big[\gamma^5\big(-i\gamma^\mu\...
0
votes
4answers
69 views

Can a single atom be a unit cell?

I was reading a pdf online and it's author said Consider the bcc lattice with single atoms at each lattice point, its unit cell can be reduced to two identical atoms. Atom 1 is at 000 and atom 2 is ...
6
votes
2answers
103 views
+50

How can $\mu$ be nonzero if grand canonical density operator commutes with $\hat{H}$?

In the grand canonical ensemble, the equilibrium density operator is given by $$\hat{\rho}_{\rm eq}=\frac{1}{Z}e^{-\beta\left(\hat{H}-\mu\hat{N}\right)}, ~{\rm with}~ Z={\rm tr}\left[e^{-\beta\left(\...
1
vote
1answer
136 views

Can two semi-infinite plane waves undergo perfectly constructive interference?

This is building off of a question I asked here. When discussing the linked problem with some friends, the consensus seemed to be that the reason two identical semi-infinite plane waves cannot ...
0
votes
1answer
22 views

Accessible States in the Ergodic Hypothesis

According to Wikipedia, the ergodic hypothesis is the assumption that all accessible microstates are equiprobable over a long period of time. My question is about the precise meaning of "...
1
vote
1answer
21 views

IR Wilson-Fisher fixed point

I was wondering how we define IR-fixed point, when we have more then one coupling. When the coupling is unique, it is simple, because we can look at the beta function of the coupling and determine ...
14
votes
2answers
827 views

Did merging Black Holes in GW150914 give up entropy and information to the gravitational waves, since they lost 3 solar masses?

Since the final Black Hole (BH) had 3 solar masses less of mass than the original binary BH, it seems the 2 BHs lost mass, and with it event surface area, entropy, and information. If that came from ...
0
votes
1answer
119 views

Momentum operator in momentum representation in polar coordinates

I would like to write Schrödinger equation in polar coordinates in momentum representation (because I have a potential depending only on distance) . Would momentum operator be still just a ...
1
vote
1answer
33 views

Regarding the quantum nature of floating gate transistor - tunneling, coherence, spectrum

In a floating gate transistor, the gate is electrically isolated. I have a few questions regarding the quantum nature of this device: It is sometimes mentioned that, to store or deduct charges from ...
-1
votes
0answers
23 views

Mach-Zehnder Interferometer operation

In a Mach-Zehnder Interferometer, which of the following represents the output state: $BS2~ M1~ BS1~ (input~ state)~ BS1^\dagger~ M1^\dagger~ BS2^\dagger$ $BS2~ M2~ BS1~ (input~ state)~ BS1^\dagger~ ...
0
votes
0answers
17 views

Deriving Lorentz Force from Faraday's Law

I am having trouble deriving the Lorentz Force,$\vec{F}=q(\vec{v}\times\vec{B})$, from Faraday's Law, $V=-Nd/dt[Psi]$. $v$ is velocity while the $V$ is voltage.
0
votes
1answer
24 views

Completeness in tensor product basis

I have a (probably simple) question about the completeness relation in dirac notation. Mostly I just want to check if I am understanding this correctly, because I can't actually find this mentioned ...

15 30 50 per page
1
2 3 4 5
3475