0
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0answers
3 views

Potential Energy in soilds :: Why are different equations used for deriving lattice constants and for deriving the properties of phonons?

While deriving the equilibrium lattice constants we use expressions for potential like lenard-jones potential which have 6th and 12th order terms or madelung energy for ionic crystals . While ...
0
votes
0answers
1 views

What is the particle, rest, and kenetic energy of a beryllium nucleus?

A beryllium nucleus has mass 6.8e-27 kg. If its speed || is 0.988c (that is, ||/c = 0.988), what are the following values? Particle Rest Kinetic My problem is that the normal formulas for the ...
0
votes
2answers
12 views

Can mass be directly measured without measuring its weight?

From Wikipedia, http://en.wikipedia.org/wiki/Mass Inertial mass measures an object's resistance to being accelerated by a force (represented by the relationship F=ma). Active gravitational ...
1
vote
2answers
19 views

Why do we use kilograms instead of newtons to measure weight in everyday life?

What was the reason to use kilograms to measure weight (e.g. body weight, market vegetables etc.) instead of using newtons?
1
vote
1answer
14 views

What is the physical interpretation of this quantity?

For the second order ODE governing the position of a projectile subject to air resistance $$ m\frac{d^2x}{dt^2} +k\frac{dx}{dt}+mg=0 \quad k>0, \> x(0)=0, \> x'(0)=V>0 $$ a ...
0
votes
0answers
10 views

What is the future of complexity theory in black-hole physics and string theory?

I found the recent work by Hayden and Harlow and Susskind very fascinating. I have also heard talks by Scott Aaronson about this emerging connection. In particular this idea of understanding ...
1
vote
0answers
7 views

Classical limit of non-interacting, relativistic quantum gas (Kapusta/Gale p.8)

I want to understand two equations in "Finite temperature field theory" by Kapusta and Gale on page 8. The partition function is $$ \ln Z = V\int \frac{d^3 p}{(2\pi)^3}\;\ln\left(1\pm ...
0
votes
0answers
10 views

How to derive the classical Gibbs entropy

I've seen the classical entropy given as $$S/k = - ∫∫ ρ(p, x)ln [ρ(p, x) h^{M}] dp dx$$ where $M$ is the number of unconstrained degrees of freedom. How do you obtain this result from the classical ...
0
votes
0answers
8 views

Fine Structure Degenerate Perturbation Theory Hydrogen

Note: We are dealing with perturbation on the states $|nlm_lm_s>$ where n is the principle quantum number, l is the angular momentum quantum number, and $m_l$ and $m_s$ are the eigenvalues of $L_z$ ...
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votes
0answers
40 views

Physics!!!! Please help me [on hold]

A device known as Atwood\'s machine consists of two masses hanging from the ends of a vertical rope that passes over a pulley. Assume the rope and pulley are massless and there is no friction in the ...
0
votes
0answers
13 views

Average force on a car [on hold]

I'm trying to find the force that acted on a car between a given seconds ..(lets say 23 & 42) (car + the passengers) = 2.34*10^3 kg (as mass) at t=23sec the car had a velocity of 20km/h[North]. ...
0
votes
0answers
26 views

Proof that the trace of the square of a pure state is always one [on hold]

Can someone provide a proof that the trace of the square of a pure state density matrix is always one?
2
votes
0answers
8 views

Why is a particular wavelength favored by transmission through a thin film?

A sheet of glass is coated with a $500\text{ nm}$ thick layer of oil ($n=1.42$). For what visible wavelengths of light do the reflected waves interfere a) constructively? b) destructively? ...
0
votes
0answers
24 views

A few questions on wave packets and uncertainty relations

According to Cohen-Tannoudji the wave-function for a one-dimensional free particle can be written as $$ \psi (x,0)=\frac{1}{\sqrt{2 \pi}} \int g(k) e^{ikx} dk.$$ While $g(k)$ is not specified, there ...
1
vote
0answers
24 views

Would an ideal gas be colder at higher altitude due to gravity?

Since gas molecules are affected by gravity, wouldn't that make gas molecules at higher than average elevation slower (at the top of their ballistic parabola) and thus colder than air molecules ...
0
votes
0answers
25 views

Why does a Ball bounce back if Forces are Equal and Opposite?

When a ball is thrown onto a wall, the ball exerts a force onto the wall. According to Newton's Third Law, the wall will exert an equal and opposite force to the ball. Thus, how would the ball be able ...
0
votes
0answers
10 views

Dicke states, spin squeezing and quantum metrology

Dicke states are by definition simultaneous eigenstates of the $J_z$ and $J^2$ operator. What is the difference between these states and Dicke squeezed (DS) states? I know that these are "entangled" ...
2
votes
1answer
29 views

Beads flying out of flask

There is a popular youtube video of some metal beads being thrown out of a flask, literally hovering out of the container My question is how detailed a physical explanation of this phenomenon we ...
0
votes
0answers
12 views

What determines the energy ratio of beta decay products?

What determines for any particular decay how much energy the electron and neutrino get? Is it just that in the CM frame of the W- the electron and neutrino are back to back, but then back in the lab ...
-1
votes
0answers
33 views

Why most problems encountered in quantum mechanics cannot be solved exactly?

Exact solutions of the Schrödinger equation exist only for a few idealized systems. Why most problems encountered in quantum mechanics cannot be solved exactly?
1
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0answers
9 views

Wigner function vs. backward kolmogorov

We know that a Wigner function is a quasi probability distribution and a backward Kolmogorov equation for a stochastic differential equation (say quantum Lagenvin equation) gives the probability ...
0
votes
1answer
49 views

Calculating number of atoms per cell in a crystal. Nonsense question in class

I don't agree at all with this question, and I think my teacher does not understand his topic. I hope you can prove me wrong. The question was this one: Potassium crystallises in a Body Centered ...
0
votes
0answers
20 views

Need advice for self study in physics [duplicate]

I need advice for self study in Physics. I have a good theoretical and practical background in math & statistics, but virtually no physics. My ultimate interest is cosmology / relativity / ...
3
votes
0answers
11 views

Cronin enhancement in p-A collisions

What is the physical picture behind Cronin enhancement in proton-nucleus collisions at intermediate transverse momentum?
-2
votes
0answers
29 views

Anybody knows about standard form? [on hold]

Based on my understanding,there are 3 basic rules but i want it to be explained fully even though i understand because somewhere deep down in the future someone is going to confuse me completely
-1
votes
0answers
16 views

What sort of things do condensed matter experimentalists measure and how?

What sort of things do condensed matter experimentalists measure and how? Do they do scattering experiments? If voltages are measured then how? I want to know what specific experiments are done. The ...
2
votes
1answer
21 views

What is an order parameter?

I've seen order parameter used in two different ways. One is to distinguish between an ordered and an unordered phase, like whether the net magnetization is stable or not. The second way is to ...
0
votes
0answers
14 views

Voltage and Electric field at a given point and time due to a sinusoidal voltage between an anode and cathode?

If have a cylindrical anode and cathode of equal length $l$, separated by a distance $d$ in a dielectric material with a relative permittivity of $\epsilon_r$ with the voltage between the anode and ...
3
votes
1answer
24 views

About Nuclear magnetic resonance

I'm trying to understand the basic principles of Nuclear Magnetic Resonance reading this link but I have some doubts: 1) I have ever known that when protons aren't in a magnetic field, their spins ...
0
votes
0answers
15 views

Conservation of linear momentum for a system with a small mass inside a cylinder

Say that you have a thin hollow cylinder with mass M on a flat ground. Inside the cylinder on its wall is a point-sized object with mass m. Initially everything is at rest. Then the cylinder and the ...
1
vote
1answer
17 views

how is an electron able to emit and absorb the same (virtual) photon?

When calculating the lowest order self energy corrections for an electron for example, feynman diagrams involving the emission and re-absorption of a (virtual) photon need to be considered, (as here ...
1
vote
0answers
40 views

Can't understand the meaning of this formula,

I've found this formula in a book and I can't understand its meaning: $$\frac{df}{dx}\biggr|_{x_0} < 0$$ It describes the condition of an object to being in a $\textit{stable}$ equilibrium. At ...
4
votes
0answers
20 views

In terms of scale, where does the concept of Reynold's number cease to have meaning?

The Reynolds number is classically described in terms of pipe geometries but its use has also been usefully extended to other more complex surface geometries to predict transitional flow behavior. But ...
-1
votes
0answers
22 views

How to convert measurements in a game world to real life measurements [on hold]

I'm trying to analyze the physics of the game Angry Birds and I'm stuck trying to scale the game up to real life measurements. The current units I am using to measure distance is the size of one red ...
0
votes
2answers
36 views

Gravitational field strength inside the Earth [duplicate]

please could someone give me a relatively straight forward answer why the gravitational field strength follows a straight line (linear) relationship with distance from the center of the Earth but when ...
1
vote
1answer
35 views

Hamilton's equations from the action with boundary conditions involving position and momentum

Generally, when you are given the action $$ S=\int_{t_1}^{t_2}\mathrm dt (p\dot q - \mathcal H )$$ the boundary conditions are $q(t_1)=q_1$ and $q(t_2)=q_2$. This is useful because to calculate ...
1
vote
1answer
44 views

If electrons aren't revolving around the nucleus, why do atoms have orbital magnetic moment?

In most introductory textbooks, the explanation of orbital magnetic moment is based on Bohr's model and electrons orbiting around the nuclues, which can be modeled as a current loop. For example, ...
-1
votes
0answers
17 views

2 fluids in a rotating U-tube [on hold]

It's an rotating U-tube, containing 2 fluids. The axis of the rotation is 0,01m dislocated to the right of the symmetry axis. I have to find the angular speed (W) so that the liquids will be leveled ...
1
vote
0answers
13 views

Functional relationship of pressure and position(1d)

so today I started doing my research on oscillations in a course on advanced mechanics. The experiment was to mathematically model the speed of sound in air and experimentally prove the usability of ...
1
vote
0answers
30 views

Physical meaning behind causal massless scalar propogator

I know that for a scalar massless field in $(3+1)$ spacetime that: $$ \langle 0 | \phi(x) \phi(y) | 0 \rangle \propto |x-y|^{-2} = (-(t_x-t_y)^2 + (\vec{x}-\vec{y})^2)^{-1}. $$ I also know that $$ ...
0
votes
0answers
14 views

Can you pull and also grind a material through a length of cylinder? [on hold]

I want to take plant matter for instance, and instead of splitting up the grinding phase and feeding through a tube phase (using a screw inside the cylinder), I'd like to combine them into one. So ...
4
votes
0answers
36 views

What experiment disproved single fluid theory of electricity?

I just can't understand how history of electricity goes on. What experiment disproved Benjamin Franklin's fluid theory of electricity?
1
vote
0answers
15 views

Induced emf in a circular conducting wheel

Consider a conducting wheel with $N \in \mathbb{N}$ spokes which is completely in a homogenous magnetic field $\vec{B}$ perpendicular to the wheel plane. ...
-3
votes
0answers
17 views

projectile motion angles [on hold]

A boy wishes to throw a ball through a house via two small openings, one in the front and the other in the back window being directly behind the first. If the boy stands at a distance of 5m in front ...
0
votes
0answers
17 views

Non-invasive inspection technique [on hold]

I am looking for a way to inspect a metal canister that is approximately 30-50 m above ground from ground level. The canister is made of Alumimnum/steel and is made of two parts and is sealed so that ...
0
votes
0answers
39 views

Pdf of particles in phase space

I am from a non-physics background and hence have difficulty in grasping the concepts some of which I need to apply in signal processing. Link1 and Link2 discuss about Liouville theorum and phase ...
1
vote
0answers
20 views

Can we prove Conservation of Angular Momentum without assuming internal forces are central?

The only proof I've seen of Conservation of Angular Momentum assumes that the internal forces of the system act along the line joining particles i and j (i.e. - all internal forces are central.) Can ...
0
votes
1answer
30 views

Centripetal force in loop motion

I saw it from the book which talk about centripetal force in circular motion The main idea here is the balance in the term of relation between velocity and centripetal acceleration - centripetal ...
1
vote
2answers
34 views

Number of revolutions of a rolling coin [on hold]

Take two quarters and lay them on a table. Press down on one quarter so it cannot move. Then, starting at the 12:00 position, roll the other quarter along the edge of the stationary quarter. How many ...

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