1
vote
2answers
24 views

How do we determine if a certain physical quantity is a vector?

For instance in Newtonian physics we treat position of objects, displacements, velocities, forces, momenta, angular velocities etc all as vector quantities (little arrows in space which have a certain ...
0
votes
1answer
28 views

Quantum Mechanics: Rotation operators

How do I know what direction of the rotation operator to use on the initial state of a spin-1/2 particle? For example, a spin-1/2 particle initially in the $\lvert y \rangle$ state enters a SGz ...
0
votes
1answer
14 views

Magnetic flux through the torroid

I am trying to derive the magnetic flux through a toroid of inner radius $\rho_0$ and outer radius $\rho_0 + 2a$, having $N$ turns I started off, by saying $$\phi = \int \vec{B} \cdot \vec{dS}$$ We ...
1
vote
1answer
14 views

Time ordering of fermion operators

If $A$ and $B$ are fermion operators then the time ordering is defined as \begin{eqnarray} T(AB) = \left\{ \begin{array}{rl} AB, & \mbox{ if $B$ precedes $A$}\\ -BA, & \mbox{if $A$ precedes ...
0
votes
0answers
12 views

Calculating the diameter of Jupiter through an image

I took an image of Jupiter through my 8" Dobsonian Telescope, attaching a DSLR and a 1.25" Barlow Lens where the eyepiece goes, as shown in this video: https://www.youtube.com/watch?v=reFxoF3XoaU ...
0
votes
0answers
2 views

Natural acoustic modes of a open-open converging or diverging duct

The fundamental frequencies of air columns depend on the length of the column, the speed of sound and the boundary conditions. For a straight duct the natural modes are $f = \frac{n ...
6
votes
1answer
523 views

Semiconductor problem: how much Boron is required to establish a certain amount of charge carrier density

The problem description is as follows: Boron is used to dope 1 kg of germanium (Ge). How much boron (B) is required to establish a charge carrier density of 3.091 x 10^17 / cm^3. One mole of ...
0
votes
0answers
10 views

Can an accelerometer be used to determine orientation of a rocket under power?

I saw a project on Hackaday featuring a model rocket with moveable fins to stabilize the rocket's trajectory: Hackaday. The goal was to arc the rocket to a horizontal trajectory and keep it there. In ...
0
votes
1answer
29 views

Conservation of Angular Momentum for an Object Not Rotating

I have a point mass connected to a string with negligible mass. The point mass has mass $m$ and is moving at a velocity $V$. The string is of length $r$, and it is keeping the point mass tied to a ...
1
vote
2answers
27 views

Can AMO physics be applicable for space travel?

I know it sounds very stupid question. I am a Ph.D student currently working on the AMO physics (Quantum Optics). I recently saw articles about the Spacex, and I thought it is really amazing, and ...
0
votes
1answer
12 views

A conceptual question related to statistical mechanics

Statistical mechanics allows us to consider an ensemble of systems, each of which consisting of only a single particle. Once we write the partition function for the system of one particle, we can ...
0
votes
3answers
17 views

Frames of reference, relativity, and a ball thrown in the air

Ever since my high school physics days I found relativity fascinating but I don't think I have great insight even into special relativity. For example, in almost every lesson or video they give an ...
0
votes
0answers
10 views

How much time a ball stays at rest when throw up?

You throw a ball straight up in the air. The ball attains its maximum height when it is momentarily at rest,(v=0). How mutch time is this moment? If we take time has continuous it is an infinitesimal ...
-1
votes
0answers
8 views

Electric Flux in a Gaussian Surface

Why is electric flux of a charge everywhere inside a Gaussian Surface constant? I want explanation ( not from any equation ).
0
votes
2answers
8 views

Water compressibility and pressure

I am so sorry if I am missing something, but for some reason I am very confused on how water can have pressure but not be compressible. If pressure is created by individual molecules bumping into the ...
0
votes
0answers
5 views

Natural timer project

I want to make a light bulb that is already on, turn off after a time that is as close as possible to 30 seconds. However, I can't use an electronic clock timer. Essentially, I just need to make two ...
2
votes
1answer
59 views

Diffeomorphism invariance and geodesic action

I'm trying to understand the role of diffeomorphism and isometry invariance in the geodesic action in GR: $$ S = \int_{\tau_1}^{\tau_2} \! d\tau~ g_{ab}(x(\tau)) \frac{dx^a}{d\tau} \frac{dx^a}{d\tau} ...
-1
votes
1answer
7 views

Net acceleration of an object if too many forces are acting on it?

Consider an object thrown upward with a force which is much greater than its weight. Obviously the object will stop after a certain interval of time due to air resistance. But what if there is no air ...
0
votes
1answer
22 views

Is linear polarization of entangle photons in 2-particle decay always correlated?

In Aspect's paper "Bell's Theorem: The naive..." and in an 2002 AJP article by Dehlinger and Mitchell "Entangled photon apparatus..." the photons are described to be in the $|xx\rangle+|yy\rangle$ ...
0
votes
0answers
16 views

Maximum temperature possible on earth

What is maximum temperature that can we have on earth? I assume that after a certain limit, radiation and convection would start working strongly to have equilibrium of surroundings. According to ...
1
vote
1answer
72 views

Is magnetism just electricity in a different FoR?

I am trying to understand magnetism and its relation to electricity: Suppose there are two electrons travelling side by side in deep space at 1 cm distance at .99 c In this article it is said that ...
8
votes
1answer
141 views

Optical chirality and its possible hierarchy of generalizations

Optical chirality refers to a constant of motion of the electromagnetic field, which measures in some sense how chiral a light field is. Specifically, the pseudoscalar quantity $$ ...
-1
votes
0answers
4 views

Working with the problems related to potential energy

Consider a spring mass system. A block is attached to a light vertical spring which is stretched under the load of block and this system is at a height h from the ground. Now my problem is that what ...
1
vote
2answers
15 views

Ampere's law for a rectangular plate?

If a conductive wire was carrying current $I$, it would create a magnetic field: $$B=\frac{\mu_0I}{2\pi r}$$ However, if it's not a wire, but instead a plate how would the expression change/adjust ...
2
votes
1answer
73 views

What is really sought when we purpose Einstein's postulates in Special Relativity?

Special Relativity can be motivated by looking at Maxwell's Electrodynamics and noticing that there is some kind of inconsistency between it and Newtonian Mechanics. Indeed, as Einstein pointed out on ...
1
vote
2answers
186 views

Viscosity calculation of a rarefied gas

I am studying the rotational-translational relaxation of a diatomic gas (like oxygen) using a GPU in order to accelerate the calculations; during the calculations I get the translational temperature, ...
0
votes
0answers
6 views

Is it possible to find the G forces of one of the axis rather than the total?

I am investigating the g-forces and acceleration experienced on roller coasters and have data for $x$, $y$ and $z$ acceleration every $0.2$ seconds of the ride as well as the total acceleration and ...
-4
votes
0answers
33 views

Formation of nucleus

Is it even remotely possible for a nucleus to be formed in the following way? Consider two nucleons approaching each other at extreme speeds. Could the relativistic increase in mass be so high to ...
1
vote
1answer
49 views

When and where to check the formal definition of a manifold

In most texts on GR we are first introduced to a formal and rigorous definition of a manifold. We then learn the point that in GR "any coordinate system" might be used for the 4D spacetime metric. ...
-1
votes
2answers
34 views

A 50 g Ice Cube with an initial temperature of -10°C is put in 400 g of water at 40°C. Find final temperature

My calculations: $$Q_g + Q_l = 0$$ $$Q_g = -Q_l$$ $$mc\Delta T = -mc\Delta T$$ $$(0.05)(2100)(T_f+10) = -(0.4)(4200)(T_f-40)$$ $$105(T_f+10) = -1680(T_f-40)$$ $$105T_f + 1050 = -1680T_f + 67,200$$ ...
0
votes
2answers
19 views

Acceleration due to gravity at Centre

Why is the acceleration due to gravity at the center of the earth $0$? My Attempt actually at the center distance from the surface is equal to the radius so the formula $$g'=(1-\frac{d}{R})\times ...
0
votes
1answer
127 views

Lenghthwise center of gravity of a boat based on flotation angle

I am trying to determine the center of gravity horizontally along the length of a pontoon boat so I can properly position the load on my lift. Approximate will do. It seems like an impossible question ...
2
votes
1answer
38 views

Does the Abbe limit hold for a single lens?

Let us say I have a single (converging lens) could I use the Abbe diffraction limit (for a microscope) to find its resolution or do I have to use the Rayleigh criterion. (i.e. Is the Abbe diffraction ...
4
votes
2answers
109 views

What manifold is spacetime?

In General Relativity, spacetime is a $4$-dimensional manifold with one Lorentzian metric tensor defined on it. In the Special Relativity case what manifold is spacetime is quite clear: it is ...
0
votes
0answers
9 views

Eddy current damping heat generation

Background According to this source (page 7): https://deepblue.lib.umich.edu/bitstream/handle/2027.42/109373/me450w10project16_report.pdf?sequence=1 the "braking" torque a magnetic field on a ...
0
votes
0answers
9 views

How does one compute the maximum height reached by the water droplets in this experiment and what is the theory behind such phenomenon?

Hot Water Fountain - Partially fill a Mohr pipette with hot water. Cover the top of the pipette with your thumb. Turn the tip upwards and observe the fountain exiting the tip. Investigate the ...
1
vote
1answer
165 views

How to calculate angle of inclination attained by a weigh balance on unequal loading?

Actually I need to rotate the beam (pivoted at centre) with constant angular velocity using the priciple of mass imbalance. Could anyone suggest what would be rate of decrease of mass in one pan ...
-1
votes
2answers
49 views

Circular motion and inclined friction [on hold]

I'm given the following picture: A car with the mass m passes the top of a hill with the height H. The coefficient of friction is $µ$. The speed of the car is $v_0$ in the moment of braking. ...
0
votes
0answers
6 views

How does the area of illumination affect the numerical aperture / optical resolution of an optical system?

I have been reading an optics paper in which they designed a microscope with the following setup. A light source passes through a small pinhole, illuminates a sample, which then forms a diffraction ...
0
votes
3answers
42 views

Axis of rotation and rotating rigid body

We know that angular momentum of a solid disk rotating with angular velocity $\omega$ is given by $I\omega$ about its center. Now if I chose any axis (parallel to above), will it have same magnitude ...
0
votes
0answers
17 views

What is the relationship between potential energy and electrical potential?

I actually always thought this was trivial, now I am not so sure. For a potential $\phi$ the potential energy is $V=q\phi$ where q is a test charge. Now I am thinking this may work differently in two ...
0
votes
0answers
7 views

Momentum of a rack and pinion gear system excited by a time variant force

Background I have a rack and pinion gear system as shown in the image below The pinion gear is attached to a flywheel at the back. The first state of the system, none of the gears or the ...
0
votes
1answer
125 views

How are Dual-energy X-ray absorptiometry (DXA/DEXA) scans affected by surface stability?

Today I had my body scanned by a GE Lunar Prodigy densitometer installed in a small RV of a company that tours California offering body composition scans (image from Wikipedia article on DXA). ...
0
votes
1answer
22 views

What determines the color of photon that is emitted from an exited atom?

I understand the principle of how light is emitted from an atom. What I don't know is why neon atom is red and copper is green when exited? Is is the distance between the electron to protons or the ...
5
votes
0answers
45 views
+50

Rope waves with a twist

In the picture you see a person walking a slackline. A slackline is a tensioned flatband of polyester. Typical tensions are between $1kN$ to $15kN$ depending on the length of the line. The lines ...
3
votes
1answer
634 views

Density of classical states in quantum theory

Let's first treat electrons as classical objects. I can evaluate the classical energy of each state in a configurational space (3N real numbers and, say, spins) using just Coulomb's law. Then I ...
2
votes
1answer
23 views

Do any approaches to a TOE expect to provide a unique solution to the universe?

The old idea of a "Theory of Everything" was that there would finally be a theory with none, or at least maybe only one or two, free parameters that would describe how the universe we live in is the ...
-4
votes
0answers
26 views

Is dt symmetrical and, if so, is 1/dt (i.e. force) conserved?

Assume $h=1$ and $1$ has no dimensions. Use dimensional analysis. Time $\left[t\right]$, distance $\left[d\right]$,, and angle $\left[<\right]$, are known to be symmetrical quanities and their ...
0
votes
1answer
28 views

Are all heaters exactly as energy efficient as each other?

I many applications, efficiency is measured in terms of how much of the input energy is wasted generating heat instead of the actual type of energy you want. For example, lightbulbs generating heat ...

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