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### 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 ...
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 ...
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 ...
36 views

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 $T_{\mu\... 2answers 29 views ### Do wormholes really allow us to travel back in time? Theories surrounding wormhole based time travel are annoying me tonight... So the way time works is relative, right? The closer you are to the frame of reference, the faster time moves. So, if we use ... 3answers 28 views ### DO I have the correct idea of time dilation? suppose that I send my twin away from the earth at 87% the speed of light. From the time dilation equation, since the twin is moving, the time interval between any 2 events, as measured by me, would ... 5answers 76 views ### How can a mass$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 ... 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 ... 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 ... 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 ... 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 ... 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 ... 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 ... 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$b$... 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 ... 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'... 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} ... 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 ... 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 ... 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? 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 ... 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 ... 0answers 16 views ### Absorption spectrum of Hydrogen why lines of Lyman series are absent in absorption spectrum of hydrogen ? 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 ... 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?... 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$$... 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 ... 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 ... 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 ... 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 ... 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 ... 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 ... 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$1/2, described by ... 0answers 6 views ### Dielectric constant of neutron ball and the behavior of EM wave in it When plane EM wave go thourgh ordinary dielectric, the small separation of atomic nuclei and the electron (i.e. dielectric polarization) will result in the dielectric constant and the slow down of the ... 2answers 270 views ### How can I determinate the air flow coming out of a pressure tank? I have a trouble with a simple question (I think). Well, if a have a tank full of compressible air at a pressure of for example 6 bar and a valve with a hole of 8 mm diameter, how can I know the ... 0answers 6 views ### When will iridescence only happen when seen through a mirror-like surface? The phenomenon is: A semi-opaque semi-rigid plastic sheet covers a window, if you see the sheet directly from any direction, there is no iridescence on the sheet. But if you see the sheet through a ... 0answers 48 views ### Lagrangian mechanics of elastic collisions How does Lagrangian mechanics apply to the elastic collision of particles? 0answers 13 views ### Proof/Derivation that a normal force applied to a rigid body object causes a torque? I saw this answer here but didn't understand it. If someone could provide a simpler proof starting from newton's second law F = ma and only using his 3 laws that would be helpful (only because I don't ... 0answers 31 views ### Trace of the log of a matrix When Zee computes the Grassmann path integral in Section II.5 of his QFT book, he uses an algebraic step I can't follow. I follow this part: \begin{align} \text{Tr}\ln\!\big[\gamma^5\big(-i\gamma^\mu\... 4answers 69 views ### Can a single atom be a unit cell? I was reading a pdf online and it's author said Consider the bcc lattice with single atoms at each lattice point, its unit cell can be reduced to two identical atoms. Atom 1 is at 000 and atom 2 is ... 2answers 103 views +50 ### How can\mu$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(\... 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 ... 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 "... 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 ... 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 ... 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 ... 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 ... 0answers 23 views ### Mach-Zehnder Interferometer operation In a Mach-Zehnder Interferometer, which of the following represents the output state:$BS2~ M1~ BS1~ (input~ state)~ BS1^\dagger~ M1^\dagger~ BS2^\daggerBS2~ M2~ BS1~ (input~ state)~ BS1^\dagger~ ...
I am having trouble deriving the Lorentz Force,$\vec{F}=q(\vec{v}\times\vec{B})$, from Faraday's Law, $V=-Nd/dt[Psi]$. $v$ is velocity while the $V$ is voltage.