All Questions

6 views

Maximum reading after dropping a mass onto a scale

If one drops an object onto a scale, the needle will temporarily spike to a high reading. Given a mass $m$ dropped from a height $h$ above a spring scale, is there a good way to approximate what the ...
6 views

Is the cosmic microwave background radiation red shifted?

My question is. If the cosmic background radiation is red shifted how would you calculate the wavelength at the time it was emitted ?
15 views

A system of particles interacting via conservative forces, will also respect $U_2+K_2=U_1+K_1$

Studying vector calculus you learn to prove that a particle moving in a gravitational field will that field that $dU=-dW$ from which you can conclude $U_2+K_2=U_1+K_1$. This is easy to prove in this ...
5 views

Thermal Imaging reflection?

I was viewing a youtube video that was about thermal imaging and saw something that caused me to ponder but I couldn't figure out an answer and the one assumption I have I don't know if it's correct. ...
9 views

Net force on magnet by fridge [on hold]

Dylan hangs a calendar on a refrigerator with a magnetic hook. Unfortunately, the magnet is too weak, so the magnet and calendar slide down the side of the refrigerator to the floor with an ...
5 views

Role of Mn in Perovskites

Good Day everyone!i don't if its the right site to ask this, but by the way, right now i'm searching for possible research in magnetoresistance properties of perovskite. So far, i already know the ...
4 views

Stack exchange for Material Science [migrated]

i just want to know if there's a stack exchange for materials science topics? Since there are stack exchange for Biology, chemistry, Physics, Programming and many more how but materials science? ...
24 views

Proof of: if $\hat H | a_n\rangle=a_n|a_n\rangle$ then $f(\hat H)| a_n\rangle=f(a_n)|a_n\rangle$?

In Quantum Mechanics you have the eigenvalue equation: $$\hat H | a_n\rangle=a_n|a_n\rangle \tag{1}$$ where $\hat H$ is the Hamiltonian operator, $\{|a_n\rangle\}$ is a complete set of eigenstates ...
11 views

Why must an inertial navigation system take the Coriolis effect into account?

I read somewhere that an inertial navigation system, in order to be accurate, must take the Coriolis effect into account. Why is this so? If I go a 500 mph velocity in a given direction, I'm going 500 ...
15 views

Are orbits possible in de sitter space?

Since the de sitter space has constant positive curvature does that mean that objects can't orbit around other objects?
13 views

Time period of bar pendulum

Why does the time period of a bar pendulum first decrease and then increase when the distance of the axis of rotation from the centre of gravity increases?
5 views

MD simulations and sputtering

can someone recommend references to study for a newbie in molecular dynamics simulation? what is sputtering in MD simulations.
21 views

6j symbols with Majorana indices

The Levin-Wen model is a Hamiltonian formulation of Turaev-Viro (2 + 1)d TQFTs. It can be constructed from a unitary fusion category $\mathcal{C}$, which can be equivalently defined using $6j$ ...
37 views

How to determine the observables rigorously?

In Quantum Mechanics, as I know, if a system is described by a Hilbert space $\mathcal{H}$, each physical quantity is associated with some hermitian operator $A : U\subset \mathcal{H}\to \mathcal{H}$ ...
25 views

Does nitrogen have the strongest bond in chemistry. If so, could a nitrogen-based material be stronger than graphene or carbyne?

Is a nitrogen-nitrogen tripple bond the strongest bond (needing the most energy to break it). is C-O bonds stronger? would aa material consisting form nitrogen-nitrogen tripple bonds be stronger than ...
18 views

The History of Dark Matter

I'm wondering if someone can give a more detailed history of Dark Matter. How did Fritz Zwicky determine that a galaxy was in 'equilibrium' given the uncertainty of a line-of-sight measurement of ...
15 views

Clocks at rest in Kruskal coordinates

The proper time in Kruskal coordinates is given by $$d\tau^2=\frac{4}{e^rr}(dT^2-dX^2)$$ (where r is measured in units of Schwarzschild radii). Since at $T=+/-\infty$, $dT^2-dX^2$ goes to zero for an ...
9 views

incompressibility of fully filled Landau level

Suppose Landau level degeneracy is 10^9, if we force to put (10^9+1) particles on the level, what extra energy will we gain? (ignore particles interactions) Like electron degeneracy pressure, ...
29 views

What do elements of CKM matrix imply?

In CKM matrix, there are 9 elements, e.g. Vud = .974, Vus = .227 ,Vub = .004. The sum of these 3 elements is greater than one, so they cannot represent the probability of an up quark to transform in ...
15 views

How does axial offset effect rotor balance?

I have a thin rod rotating about its primary axis, rigidly attached to mass $m_1$ whose center sits at distance $r_1$ from the axis and position $y_1$ along the axis. $m_1$ exerts a centripetal force ...
13 views

What is the value of coupling constant at electroweak unification?

The value of running coupling constant is (1/24) at grand unification energy,where strong, weak & electromagnetic forces are unified and in a graph between running coupling constants vs ...
16 views

Force required to hold aerialist

Hanging on a trapeze, one aerialist holds the other by both arms. It is easier for the first aerialist to hold his partner still or to swing him? Assume the swing continues to swing under it's own ...
32 views

Find constant acceleration with only initial speed and distance

Given the problem: "A car moving initially at 50 mi/h begins decelerating at a constant rate 60 ft short of a stoplight. If the car comes to a stop right at the light, what is the magnitude of its ...
46 views

Vector calculus problem [on hold]

I have to solve this: $$[(\nabla \times \nabla)\cdot \nabla](x^2 + y^2 + z^2)$$ But I am really drowning in the sand.. Can anybody help me please?
45 views

Entanglement and coherence

I have come across a wonderful review of entanglement by Chris Drost in his answer to this post. One part that left me puzzled was: (This post is merely an attempt to understand a portion of Chris' ...
327 views

Do black holes violate the first law of thermodynamics?

When a black hole absorbs matter is it destroying that mass, thereby destroying energy, therefore violating the first law of thermodynamics?
21 views

Deriving velocity after elastic and inelastic collision via the Principle of Least Action

I am reading on the Principle of Least Action from a historical perspective. I am also trying to make sense of it from a contemporary point of view -- though my training in contemporary physics is ...
14 views

Can we know the limit of the number of times information can be stored/retrieved in computer chips - hard disks and RAM?

I was wondering whether the memory storage of a single memory area in computer semiconducotrs is limited in terms of the number of times we use and if I am at the edge of using it up, will it stop ...
52 views

Wavefunctions in different Hilbert spaces

The state of a quantum system is represented by a wavefunction usually in some specific Hilbert space, .e.g of position, spin, momentum etc. But before deciding in which of these bases to decompose ...
26 views

A question on deriving a formula for a rotational object

I have this question assigned, but I really am stuck on how to do it: A bullet is shot through two cardboard disks attached a distance $D$ apart to a shaft turning with a rotational period $T$, as ...
41 views

27 views

Shielding of electric and gravitational force on particles inside a spherical shell

A cavity inside a conductor is shielded from outside electric influences. But, if you put charges inside the cavity, the exterior of the conductor is not shielded from the fields by the inside ...
16 views

Using fiber optics to focus quartz tungsten halogen light

Our purpose is to make 1 mm spot size of quartz tungsten halogen light with 100 mm working distance for spectral imaging of wavelengths of 350-2000 nm. With some QTH light source and adapter on the ...
31 views

Periodicity of function as a result of superposition in Quantum Mechanics

Say we add infinitely many waves (states of definite momentum) so as to produce a function that gives a very well-defined position, does that addition(using Fourier series) make that function ...
40 views

Superposition of waves with different initial phase in Quantum Mechanics

In Quantum Mechanics, if a particle's state is a superposition of many states of definite momentum, then we say that it's position is well-defined (by the Heisenberg uncertainty principle, because ...
15 views

Dipoles in an external rotating field?

Consider a bunch of magnetic dipoles in $x-y$ plane in an external magnetic field $B(t)=B_0 \hat{z}+B_1(cos\omega t~\hat{x}+sin\omega t~\hat{y})$. The dipoles are rotating around $z$ axis and of ...
27 views

Manometer & pressure

I have trouble with a homework question in understanding how the manometer liquid responds to pressure changes. Any help will be much appreciated. The problem goes like this: A cylinder of diameter ...
18 views

total vorticity generation in 3D

In 2D flows, the total vorticity generation for an impulsively started plate can be found by measuring the circulation of the flow. This gives the vorticity generated per unit length. I would like ...
8 views

How to obtain a lower mass bound for a unstable (or stable) particle from Poisson statistics?

Imagine you have a particle (stable e.g. if some R-symmetry or similar does exits) heavy or not so heavy... Question: how to guess a lower (upper bound as well) with the aid of Poisson statistics, ...
31 views

Why does ice fall from the top of the ice tray first?

I haven't found an answer for this anywhere, so hopefully this community can help. It's not important at all that I know this but I'm curious. If you take a plastic tray of ice from the freezer and ...
22 views

In my textbook, we calculated the rate at which an electric dipole radiates energy to be $Pwr = \frac{1}{4\pi \epsilon_0}\frac{2}{3c^3}\left(\frac{d^2 p}{dt^2} \right)^2$ where p is the dipole ...