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1answer
39 views

Why doesn't the Normal reaction force on surface and the weight $mg$ add up?

I was learning about normal reaction force today and I saw a diagram like this: My questions about this are: Are $\mathbf {N_1}$ and $\mathbf {N_2}$ same in magnitude? Why don't $\mathbf{N_2}$ and ...
1
vote
1answer
68 views

Why we don't see a spectrum of colours above water?

Why we don't see a spectrum of colours above water? When a light ray enters the water it will become dispersed, and after reflecting from an object in the water, say a pencil, or just the bottom of ...
-1
votes
0answers
25 views

Newton’s third law understanding [duplicate]

We have boxes and we are picking up a wood and put in between our hand and the box. We start pushing wood with 20N force. This force Is transferred from wood to the box and box return 20N to wood (...
-2
votes
0answers
31 views

Where does exactly this classical model of the hydrogen atom fail? [duplicate]

I know that classically, the hydrogen atom consists on an electrostatic interaction between the electron and the proton, with masses $m_e$ and $m_p$ respectively, with charge $e$. For the sake of ...
1
vote
1answer
49 views

Inverse Square Law of Radiation

I am conducting an experiment in which I investigate the relationship between the counts per second detected by a Geiger Counter and the distance between said Geiger Counter and the source of ...
-2
votes
0answers
25 views

On the classical model of the hydrogen atom and its virtues and defects [closed]

What is the classical Hamiltonian of the hydrogen atom? How to model the hydrogen atom using classical mechanics? I know that we have two point particles with masses $m_e \approx9.11*10^{-31} \mathrm{...
0
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0answers
8 views

Quantifying Resistance Band Tension

I am undertaking a small investigation into the effects of resistance bands applied to dynamic activity (in this case a squat). As part of this I'd like to quantify band tension throughout the ...
0
votes
1answer
45 views

Maxwell equation in tensor form

I have seen many times on different sources that the equation: $$ \epsilon^{\mu\nu\rho\sigma}\partial_{\nu}F_{\rho\sigma}=0$$ Is true identically following from it being a product of an anti-symmetric ...
2
votes
2answers
40 views

Why do spontaneous emission and absorption alone violate thermodynamic laws?

Einstein suggested that stimulated emissions must also occur along with spontaneous emission and absorption, because the latter two alone violate thermodynamic laws. How exactly do spontaneous ...
0
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0answers
22 views

$|E_c - E_f|$ in Silicon doped with acceptors

I've been trying to figure out how does Fermi energy $E_f$ changes with Temperature $T$ In Silicon with doping density $N_a = 10^{18}\ \ [cm^{-3}]$ In short the question is: $|E_c-E_f|$ rises ...
1
vote
1answer
41 views

Viscosity in fluids is like kinetic friction between solids. But what is the fluid-equivalent of static friction?

Viscous stress is proportional to $\frac{du}{dy}$, so they only arise from relative motion between different layers of fluid. That makes it somewhat similar to kinetic friction, which requires ...
0
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0answers
33 views

The helicity and spin conservation in the $e^+e^-\rightarrow \mu^+ \mu^-$ process

A related post was What is polarisation, spin, helicity, chirality and parity? In $m_\mu<<E$ region, $m_\mu$ could be treated as massless particles and the conservation of helicity indicated the ...
0
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5answers
107 views

Why is Newton's law of restitution true, or how to prove it?

Question. If we just consider a one-dimensional collision between two objects (ignore friction as well), Newton's law of restitution states that the speed of separation after the collision divided by ...
6
votes
4answers
512 views

Had scientists ever fired single protons/electrons/particles before Einstein's work on the photoelectric effect?

Had scientists ever managed to fire/detect single, individual particles, photons/electrons/etc., before the photoelectric effect was discovered and Einstein's work on it saying that light also acted ...
0
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0answers
12 views

What are the nuclear excited spin/vibrational states of tritium? Further, what are the transitions to ground from those?

i performed a title search in arXiv with "tritium" included, 48 results, 25 article downloads, 48 abstracts read twice, not a single article has basic data on tritium, does any here know of ...
1
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0answers
13 views

Are new Moons (and full Moons) more probable to happen around certain ecliptic longitudes?

The average lunar synodic month is 29.53059 days. Because of these variations in angular rate, the actual time between lunations may vary from about 29.18 to about 29.93 days. The average duration in ...
0
votes
2answers
74 views

Adding equal and opposite vectors in polar coordinates without transforming into cartesian

Suppose that you have two force vectors, $\vec{F_{1}}$ and $\vec{F_{2}}$ in polar coordinates such that they have equal magnitude and opposite angles, $\theta$ as defined below. $$ \vec{F_{1}} = r\...
2
votes
1answer
43 views

Complex Tensors and Metric

It has been given that in 2-dimensions, consider the metric: $$\ ds^2 = e^{\phi(z,\overline z)}dzd\overline z .$$ Show that $$\ t_{z...z;z} = (\partial_{z} - n\partial_{z} \phi)t_{z....} .$$ I can't ...
2
votes
0answers
41 views

Probability density for a Markov process with Gaussian two-point functions

The problem Consider a stochastic process with the following three properties: The process is Markov, meaning that $p(x_n,t_n|x_{n-1},t_{n-1},\ldots x_1, t_1) = p(x_n,t_n|x_{n-1},t_{n-1}).$ The ...
0
votes
0answers
38 views

Information about Guidry's book "Modern General Relativity", CUP (2019) [closed]

I've seen there's already a section devoted to some advices about GR books, anyway I recently came across the book whose title I quoted above, "Modern General Relativity", CUP (2019), by ...
0
votes
2answers
26 views

Transforming Moment of Inertia/Angular Momenta in Lab Frame for Rigid Bodies

This is just a quick question about transforming rigid bodies. Suppose we have a problem where we can find the moment of inertia tensor of some rotating rigid body in the body's frame (take it as ...
2
votes
2answers
132 views

Black holes with no space-time (metric)?

It is generally accepted that a black hole can be defined as a trapped surface or region of space-time where gravity is so intense that light can not escape. Another definition is that a black hole is ...
-1
votes
2answers
36 views

Angular Displacement and Angular Position [closed]

A particle starts from the positive y-axis and makes 3 full revolutions around the origin (anti-clockwise) and then turns back by 60 degrees (pi/3 radians) (in the clockwise direction). Find its ...
0
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0answers
16 views

Total moment around the centroid of an inverted pendulum

Why are both forces generate negative moments around the centroid of the pendulum in the following free body diagram? Shouldn't P generate a positive moment?
0
votes
0answers
53 views

Is $\frac{1}{e^{\beta(E-\mu)}}= \frac{e^{\beta E_k}}{\sum_{k=1}e^{-\beta E_k}}$?

I was reading a Quantum fluids book, in the introduction say that the Boltzmann Distribution is: $\frac{1}{e^{\beta(E-\mu)}}$ but I don't understand the relation between the Boltzmann distribution ...
1
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0answers
28 views

Acceptability of Linearized General Relativity with Exact Linear Metrics

Linearized general relativity is typically employed when gravity is weak, and the metric can be approximated as a perturbation of a (usually flat) background metric. However, for some classes of ...
1
vote
1answer
31 views

Where do I see the difference in Majorana vs. Dirac pair annihilation?

If I have a Lagrangian density $\cal{L}=\bar{\chi}\gamma^{\mu}{\rm A}_{\mu}\chi+\bar{f}\gamma^{\mu}{\rm A} _{\mu}f$ and I calculate the diagram $\chi \bar{\chi}\to f \bar{f}$ where $f$ is (let's say) ...
1
vote
0answers
47 views
+50

QED vacuum as a classical dielectric medium?

I have heard this analogy a few times, particularly in the context of vacuum polarization. To what extent can the QED vacuum be modeled as a classical dielectric medium? Can one compute effective ...
0
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0answers
40 views

Simplified effect of viscosity on flowrate when flowing from a cylinder through a small hole?

I'm writing a high school project and am studying the effect of viscosity on the flow rate when a Newtonian liquid (concentrated sugar with water) flows out of a hole (let's say of radius r << ...
0
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0answers
34 views

Will gravity ever fade over, considering all variables constant? If not, why? [closed]

Even when all variables constant, would gravity ever fade..?
2
votes
3answers
225 views

Why is this Taylor Expansion, Leading to the Boltzmann Distribution, Acceptable?

In Stephen Blundell's "Concepts in Thermal Physics" chapter 4 he derives the Boltzmann distribution. The equation that leads to the Taylor expansion is the following: $$P_s(\epsilon) \propto ...
1
vote
1answer
55 views

Would a human be able to descend to depths in the ocean that would crush their body?

Would not the same forces that would crush the body also resist descent? Or would the body be too buoyant to descend below the point at which the water would crush a human?
0
votes
2answers
39 views

Excavated cylinder rolling down ramp

I am wondering about this problem. I have a uniform cylinder of radius $a$ with a hole of radius $a/2$ in it which rolls without slipping down a fixed, inclined plane and I want to know it's speed at ...
1
vote
1answer
87 views
+100

Different adjoints in particle physics

I am currently reading Quantum Chromodynamics on the Lattice by C. Gattringer C.B. Lang and I am confused about an expression in the book. The expression is $$\langle \text{tr}[S(\textbf{m}, \textbf{n}...
1
vote
2answers
45 views

Is it the term "telescope" the same as a "detector"?

For example, in this reference, MITO: muon telescope they use the term telescope but clearly the "telescope" is a muon detection system. And they also talk about angular resolution, angular ...
-1
votes
1answer
66 views

Is a conservation/symmetry law behind wave-particle duality?

Please help me in solving a question stuck in my head about symmetry and conservation laws? Can wave-particle duality be considered an atomic-particle symmetry? And if so, what is the conservation law ...
0
votes
0answers
28 views

Spin 1/2 in a fluctuating magnetic field

I study mathematics at a university, and one of my courses is physics. I got puzzled by one of the problems in my latest assignment in that course and hope to get a clarification here. Here's my ...
0
votes
1answer
34 views

Does the size of a drop of water matter inside the microwave oven?

My understanding of how a microwave oven operates is that the oscillating electric field causes an oscillating torque on the electric dipole of water molecules, making they vibrate. This vibration ...
0
votes
2answers
32 views

Apparent weight in diurnal motion

An object of mass $m$ is on the equatorial plane. Now it is moving in a circle of radius equal to the radius of earth $R$. The object is moving with angular acceleration $\omega$. Let us observe from ...
0
votes
0answers
22 views

Helmholtz free energy and equilibrium, examples

I've read that a system for which temperature is kept constant is in thermodynamic equilibrium if Helmholtz free energy is minimized. Can someone makes me an example of a system for which temperature ...
1
vote
1answer
75 views

Which of these sentences best describes the equivalence between mass and energy? [closed]

Which of these sentences best describes the equivalence between mass and energy? mass is a form of energy. mass and energy are two manifestations of the same property: mass-energy. mass is energy ...
0
votes
1answer
21 views

In Drude model of conduction, are electrons moving across the conductive object?

As I understood, Drude model explains an electrical current as a chain of momentum transfer between electrons; In this sense, does a single electron leave its atom and move forming the electrical ...
1
vote
0answers
35 views
+100

Conceptual explanation for subsonic nozzle VS supersonic nozzle

A nozzle is a device that increases the velocity of a fluid in the expanse of pressure energy drop of the fluid (The Bernoulli principle). Now how can we explain (conceptually, no math) why a subsonic ...
-5
votes
1answer
123 views

Real space trip to a star e.g. Alpha Centauri [closed]

Assume a person can travel as fast as they want with $v_{max} = c$ and $a_{max} = g$ . They want to make a round trip to the nearest star, 4.2 light years away. That person experiences the trip to ...
0
votes
0answers
17 views

Possible relation between internal and external magnetic field in Neutron Stars

I am wondering about a topic that disturbs me and regarding which I haven't found enough literature about. Neutron stars are thought to be highly magnetised objects. Generally one makes the ...
2
votes
0answers
37 views

Solution to two-dimensional PDE (wave/Klein-Gordon type equation)

I'm cross-posting from the Math SE as more people might have relevant knowledge here. I was playing with an optimization problem and ended up reducing it to solving the following PDE: $$ a^2 xy \frac{\...
-1
votes
0answers
41 views

If the physical universe is a simulation, wouldn't nested recursion of universes "overload" the host simulation? [closed]

Context Suppose we do live in a universe which is simulated. Now how that would work is unclear obviously, perhaps the simulation of broader perception (rendering a chair, but not the individual atoms ...
1
vote
1answer
66 views

Is it Possible for a System to have Negative Absolute Temperature?

The statistical definition of temperature is the following: $$\frac{1}{k_BT} = \frac{d\ln(\Omega)}{dE}$$ where $k_B$ is the Boltzmann constant, $T$ is the temperature, $\Omega$ is the possible number ...
0
votes
0answers
20 views

Deriving the scale factor in a closed universe by solving this differential equation

In Carrol and Ostlie's "An Introduction to Modern Astrophysics" this differential equation is presented: and then solved it for a flat universe (k=0). But for the case of a closed universe (...
1
vote
0answers
69 views

When is it necessary to quantize the electromagnetic field?

I've seen both classical and quantized electromagnetic fields in quantum mechanics problems - for example, classical in linear response and the Coulomb interaction, and quantum in photon absorption - ...

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