1
vote
2answers
41 views

How would a plane hitting a ball move (opposite of Pong)?

When a moving ball hits a stationary plane at an angle of incidence to the normal, it bounces away at the same angle (the angle of reflection), which is commonly understood. My question is 1) What ...
1
vote
1answer
33 views

How to derive $r, \theta, \phi$ for the sperical coordinate gradient?

I'm trying to figure out how to get the gradient in spherical coordinates. I'm as far as the author writes in this answer: http://physics.stackexchange.com/a/78514 and I understand how and why to get ...
2
votes
2answers
64 views

Will the day/night cycle change when the poles melt?

I want to know what will happen to day and night if poles melt i think it will change but I don't know why? ^_^
0
votes
0answers
25 views

Total Energy of Inverted Pendulum

I have to find the total energy $V$ of an inverted pendulum (rod). The following parameters and their values are given: Mass $m$ and length $l$ of the pendulum $\theta$ as the angle of the ...
3
votes
1answer
40 views

In an elastic collision, can we choose between cons. of energy and cons. of momentum?

Suppose we have two solid spheres with masses $m$ and $M$, respectively, and that $m$ is significantly smaller than $M$. The lighter sphere is placed directly on top of the heavier one, and the two ...
0
votes
1answer
89 views

Path Difference Due to Angled Incident Light

If light incident on a diffraction grating makes an angle $\alpha$ with respect to the normal to the grating, show how $$m \lambda = d\sin\theta$$ becomes $$m\lambda = d[\sin(\theta - \alpha) + ...
0
votes
0answers
30 views

Physical interpretation of legendre transformations in thermodynamics

I have found this question(Physical meaning of Legendre transformation) and I have some questions regarding the transformations in thermodynamics, In thermodynamics we have: $$H= U+PV $$ $$F=U-TS ...
0
votes
3answers
37 views

How does $p=fv$ hold when $v=0$ and an engine is working?

Standard high school equations: Work = Force x Distance Power = Work / Time = Force x Distance / Time = Force x Velocity When a space rocket takes ...
0
votes
0answers
33 views

The structure of spacetime and entanglement [on hold]

how many ways to quantize gravity? Do they contradict each other? How to apply long-range entangment/Professor Wen Xiaogang's theory to virtual pairs
1
vote
3answers
49 views

In aircraft design why are light materials preferred to heavy ones?

Especially given the relative cost between (say) steel and carbon composites. After all, I assume most fuel is consumed overcoming drag not accelerating mass. Once an aircraft reaches cruising speed ...
0
votes
0answers
13 views

plasma and infinite acceleration

I am trying to set up a simulation of particles (they are not any particular kinds of particles, they are just points that repel each other). All the particles repel each other through the inverse ...
0
votes
1answer
26 views

“Definition” of internal energy

Conversation of energy implies that if we have a thermally insulated system which goes from state 1 to state 2: $$\Delta E_{12}=E(2)-E(1)=\Delta W_{12}$$ and the 1st law of thermodynamics ...
20
votes
7answers
3k views

Does it take more energy to open a door when applying force close to the hinge?

Assuming an ordinary hinged door (without any springs), would it take more energy to open it when applying force in the middle of the door (point b), rather than at the end of the door (point a), ...
4
votes
1answer
285 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic ...
-2
votes
0answers
9 views

Calculate bicycle efficiency power transmission?

How can I calculate the efficiency of power transmission from a person to a bicycle with standard flat pedals? How can I calculate the efficiency of power transmission from a person to a bicycle with ...
1
vote
1answer
44 views

Can a hypothetical universe have more than 2 types of its dimensions?

Our universe is often described as having 3 space-like dimensions and 1 time-like dimension. Can hypothetical universe exist with more than space and time like dimensions? If so how would these ...
-3
votes
0answers
24 views

What would happen if a space ship may travel as quickly as the speed of light? [on hold]

Ofcouse, it is impossible. Beacuse of need of infinite energy to accelarate infinite mass... Bur if it might be possible...??? I did a fictional study as an amateur. I shared it, but i need feedback ...
3
votes
2answers
130 views

How to interpret single photon interference when the two possible paths are different in length?

Here is my question. I struggle with the definition of single photon interference. Let’s assume we have a Michelson interferometer and the interference pattern we observe is a single photon result, ...
2
votes
1answer
29 views

How does the second law of thermodynamics affect the efficiency heat-to-work conversion, at the molecular level?

I understand the second law of thermodynamics in terms of the improbability of the high--and-low-velocity particles of a gas to separate themselves so that at one moment they are at different sides of ...
0
votes
1answer
47 views

Quantum state of a system after measurements with non-commutative operators

a) Assume two operators $A$ and $B$. 1) Assume $$[A,B]=0 $$ and $$ ψ= \sum c_n u_n ~~~~\text a~ wavefunction~ describing~ the~ state~ of~ the~ system $$ with $$Aψ=a_n u_n $$ $$Bψ=b_n u_n$$ If we ...
0
votes
0answers
20 views

Another universe in the other side of a black hole? [duplicate]

A common notion is that there is another universe in the other side of a black hole, past the singularity point....is this true? does it have any scientific support?
1
vote
2answers
606 views

How do magnets work?

I've read a classbook on the field theory (including EM): it perfectly describes quantitive patterns in EM-theory, but I have no luck understanding how and why it works. I mean, magnetic substances ...
7
votes
2answers
916 views

Deriving Birkhoff's Theorem

I am trying to derive Birkhoff's theorem in GR as an exercise: a spherically symmetric gravitational field is static in the vacuum area. I managed to prove that $g_{00}$ is independent of t in the ...
0
votes
2answers
22 views

What is the formula of power of an optical instrument?

I have searched and found that the power of a lens, with surrounding medium of refractive index $n$, is $n/f$ where $f$ is the focal length, the formula is $$n/f=(n'-n)/R1 + (n-n')/R2.$$ But in my ...
-3
votes
0answers
14 views

How would I prove the gamma normalization relation without Clifford Algebra? [duplicate]

The equation in question is $$ \left ( \gamma ^{\mu } \right )^{\dagger }=\gamma ^{0}\gamma ^{\mu }\gamma ^{0}$$
1
vote
0answers
29 views

Birkhoff Theorem proof reference [on hold]

I am looking for a reference with a clear (and easy to understand) proof of Birkhoff's theorem in general relativity.
5
votes
2answers
740 views

How to solve bound states of 2D finite rectangular square well?

I want to solve bound states (in fact only base state is needed) of time-independent Schrodinger equation with a 2D finite rectangular square well \begin{equation}V(x,y)=\cases{0,&$ |x|\le a ...
0
votes
0answers
45 views

how to define infinite/finite systems in nature?

Infinity may be fixed and limited in a set, sequence, or series to repeat the same things infinitely and the finite is not fixed/unlimited to repeat different things finitely. Both can be described by ...
-1
votes
0answers
21 views

Solving IVP $\frac{dE}{dx}= -\gamma\frac{dx}{dt}-\alpha$ [on hold]

I need to solve the differential equation $$\frac{dE}{dx}= -\gamma\frac{dx}{dt}-\alpha$$ with the initial value $$v(t=0)=v_O$$ I tried writing everything in terms of $v$ which gives me: ...
-5
votes
2answers
59 views

Is it possible to travel ONLY through Time and not Space?

The question is as stated above. I although think, the most probable answer is no, but I really want to know the reason to it. If, One can travel through only space by travelling at the speed of ...
-3
votes
1answer
40 views

In Gauss's law, why do we use an infinte long wire or long plane to calculate electric field intensity?

In the NCERT textbook of class 12, in the section on applications of Gauss's law, there are three applications. The first application is to calculate the electric field intensity around an infinitely ...
-1
votes
0answers
30 views

Sinusoidal Wave Problem [on hold]

A sinusoidal wave of frequency $650 \mathrm{Hz}$ has a velocity of $450 \frac{\mathrm{m}}{\mathrm{s}}$. Determine the distance between two points on the wave that differ in phase by 1.5 ...
-1
votes
0answers
19 views

XRD of Graphene Foam

At what 2$\theta$ values Graphene Foam shows the peaks in XRD ? I got two peaks at 2$\theta$ values 14.7 degree and 17.2 degree..
-2
votes
0answers
41 views

Establish a relation between height of the water column and time in a spherical container with a hole in the bottom [on hold]

Suppose we have half of a sphere of radius $R$ filled with water. In the bottom of the container there is a hole of area $S_0$. Velocity of the water flow out of the hole is $$V=\lambda(2gh)^{1/2}.$$ ...
-1
votes
0answers
15 views

Clocks in moving inertial frames [on hold]

A clock $C$ is at rest at the spatial origin of an inertial frame $S$. A second clock $C'$ is at rest at the spatial origin of an inertial frame $S'$ moving with constant speed $u$ relative to $S$. ...
0
votes
1answer
32 views

System of two harmonic oscillators and its quantum partition function

Consider a system of two harmonic oscillators with different frequencies $\omega_1,\omega_2$ and masses $m_1,m_2$ so the hamiltonian is $$\mathcal{H}(p_1,q_1;p_2,q_2)=\sum_{i=1}^2 ...
1
vote
0answers
8 views

Wave velocity (R)LC circuits.

I'm attempting to simulate some fluid like mechanics using circuits. Specifically wave propagation. I am attempting to measure the wave propagation velocity using an oscilloscope on the circuit below, ...
1
vote
1answer
260 views

Force on a coil inside of a voice coil

as a homework exercise we were given the following question: Given the following voice coil: With depth = 20 mm Permanent magnets with B = 1.23 T, Ur = 1.1 The coils has 20 turns, I = 1 Ampere. a) ...
1
vote
1answer
37 views

Would an undersea reverse osmosis station work?

According to Wikipedia, saltwater reverse osmosis occurs at 600-1200 PSI. Saltwater adds .455 PSI per foot, so 900 PSI would be at a depth of about 1980 ft or 603 meters. This is about halfway ...
2
votes
1answer
108 views

If a hot Jupiter was not tidally locked, then are there any specific cases where its wind speeds would be milder than those found on Jupiter?

If a hot Jupiter was not tidally locked, are there any specific cases where its wind speeds would be milder than those found on Jupiter? After controlling for the age of the hot Jupiter, of course. ...
1
vote
1answer
30 views

Digital colors: why RGB instead of RYG? [duplicate]

We know that Red, Yellow, Blue are primary colors. Any other color can be created by mixing these color. Graphical representation is below: But when I began to learn about computers, I noticed that ...
-1
votes
2answers
67 views

Why do we see light and isn't everything dark?

Suppose it is dark. If someone shines a flashlight directly at you, you see light. If, however, someone shines a flashlight at something else, you see that thing illuminated, but you don't see the ...
3
votes
1answer
289 views

Hubbard Model Hamitonian

$H = -\sum\limits_{i,j} A_{ij} c_i^{\dagger} c_j + \frac{U}{2} \sum\limits_i(c_i^\dagger c_i)(c_i^\dagger c_i -1)$ is defined to be a Hamiltonian for modeling quantum random walk of identical ...
0
votes
1answer
37 views

Zero volume at zero Kelvin

Why does the volume of a gas become zero at 0 Kelvin? Can a Bose Einstein condensate be considered as matter? (I mean the volume becomes zero)
1
vote
1answer
48 views

Why do really powerful magnets have to be really big?

If you want to make a really powerful magnet, that can for example attract golf ball sized metal objects from 15 feet away, the magnet has to be really big, and really heavy. Why is this so? I don't ...
0
votes
0answers
67 views

Schrödinger Equation [on hold]

Thank you for putting my question on hold. If you will allow me a few days, beyond this weekend, to adequately rephrase the question. I need the time to find a local physicst/math professor to aid ...
3
votes
2answers
800 views

Can conservation of momentum be violated?

The law of the conservation of momentum has been established for hundred of years. Even in Quantum field theory every particle collision must be momentum-conserving if there is homogenity in space. ...
2
votes
1answer
209 views

Question on derivation of Ward identity

I'm currently reading these notes about the Ward identity (pages 259 - 261). I will repeat some of the steps to make the question self-contained. Let us consider a local transformation on the field ...
4
votes
1answer
64 views

Historical Survey of Statistical Mechanics

Statistical mechanics is a subject with a particularly rich history. I think of the early debates of Boltzmann and Loschmidt, the rather confusing differences between the approaches of Gibbs and ...

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