3
votes
3answers
147 views
How does relativity explain gravity, without assuming gravity [duplicate]
I have seen the "objects pull down on space-time" explanations, but they assume a "pull down" force themselves. Could anyone explain the space-time explanation without assuming gravity in the first ...
3
votes
2answers
53 views
Does the slip-stick phenomenon have any application?
The slip-stick phenomenon is present all around us, be it the noise of car breaks or in earthquakes. But does it have any real-life application?
0
votes
1answer
53 views
Computing $\Delta m$ in $\beta^-$ decay
$\require{mhchem}$What is the energy $Q$ released when $\ce{^131_53I}$ decays and $\ce{^131_54 Xe}$ is formed? The atomic mass of $\ce{I}$ is $130.906118~u$ and the atomic mass of $\ce{Xe}$ is ...
0
votes
1answer
40 views
How does gravity effects both time and light if they have no mass [duplicate]
I've been reading about how black holes can effect both time and light with gravity. So I was wondering, doesn't something have to have mass to be effected by gravity? And if so, does this mean both ...
18
votes
1answer
299 views
+300
Does a charged or rotating black hole change the genus of spacetime?
For a Reissner–Nordström or Kerr black hole there is an analytic continuation through the event horizon and back out. Assuming this is physically meaningful (various site members hereabouts think ...
0
votes
0answers
33 views
Derivative of $\epsilon$ in lennard jones equation
I just want to calculate the derivative of epsilon for the following Lennard Jones equation:
LJ = $4\sqrt{\epsilon_{ii} \epsilon_{jj}}$ $[(\sigma/ r)^{12}-(\sigma/r)^{6}]$ with respect to ...
0
votes
1answer
25 views
Eigenvector Grover Operator
I have a question about the eigenvectors for the evolution operator of Grover's algorithm. Let $U=R_DR_f$, where
$$\begin{align*}
R_D &= 2|D\rangle\langle D| -I_N , \\ R_f &= ...
2
votes
2answers
43 views
What really is the Magnetic Force on a wire?
I have a doubt regarding the significance of a force on a wire. Well, first of all, I know that if I have a particle and if there are several forces acting over it, then we can compute one total force ...
1
vote
1answer
37 views
Electromotive Force Definition for Induced Current
If in DC , Emf is the work done to carry a unit positive charge from -ve to +ve terminal .
What is induced EMF then , in a similar sense ? To carry a unit charge around a loop once along a fixed ...
0
votes
1answer
51 views
rate of flow out of a reservoir
A reservoir contains a fluid, and there is an aperture at the bottom through which the fluid flows out as shown in the illustration:
I understand that the rate of flow is based on at least these ...
2
votes
3answers
80 views
Question about the proof that heat capacity goes to zero if temperature approaches $0K$
I don't completely understand the proof that is given for the claim that the heat capacity goes to zero, if the temperature approaches $0K$.
They do it as follows, if $C_x$ is the heat capacity where ...
0
votes
1answer
34 views
Calculating vector components from other vectors
I'm busy studying for my Physics exam this evening and I've come across a vector problem that I cant quite solve. Any help would be appreciated!
We are given the following vectors:
...
5
votes
2answers
291 views
Does rotational energy have effect on gravity/metric?
Intuitively, if energy can be stored in rotational motion, it has to obey $E=mc^2$.
Does rotation of typical stellar-sized objects - BHs, pulsars, binaries - have measurable effect on their overall ...
9
votes
1answer
167 views
Lagrangian for Goldstone mode + topological excitation
The XY-model Hamiltonian is the following,
$${\cal H}~=~-J\sum_{\langle i,j\rangle} \cos (\theta_i -\theta_j).$$
The Goldstone mode corresponds to term $(\nabla \theta)^2$ in the effective ...
2
votes
1answer
102 views
Doubts about the definition of mass
I'm having some problems understanding what are the possible definitons of mass and how they are related to each other.
In Classical Mechanics, we can distinguish between inertial and gravitational ...
2
votes
3answers
122 views
What is the general statistical definition of temperature?
Temperature in an isolated system is defined as:
$$\frac{1}{T} = -\frac{\partial{S(E,V,N)}}{\partial{E}} $$
But I wonder how one can generalize this to a random system.
Or for instance to a point in ...
-2
votes
0answers
29 views
About machine having efficiency infinite [closed]
I do not have any idea, about how to share my view but it is possible to make machine having efficiency infinite. From last 12 years I am constantly working on it and i have found a solution but up ...
0
votes
0answers
19 views
Is a dynamical extension of non-commutative black holes feasible?
Non-commutative (sometimes called "fuzzy") black holes are solutions of Einstein's equations obtained with a previous basic assumption of non-commutativity of the coordinates $[x^{\mu},x^{\nu}]=i\, ...
0
votes
0answers
44 views
Gradient involved commutator in $\phi^4$ theory
In a phi fourth theory, the Hamiltonian density is:
$$\mathcal{H}=\frac{1}{2}\pi^2+\frac{1}{2}(\nabla \phi)^2+\frac{1}{2}m^2\phi^2+\frac{\lambda}{4!}\phi^4$$
Now I impose the usual equal time ...
0
votes
0answers
14 views
What is the “relative permeability” of Neodymium?
I am currently interested in finding a high "relative permeable" material to put into the core of a solenoid. However many sources quote Neodymium's recoil realtive permeability ($\mu_{rec}$) to be ...
0
votes
0answers
30 views
fast quantum random number generator + limited decoherence rate => Schrödinger cat state?
Suppose that fast quantum random number generator (QRNG, https://qrng.physik.hu-berlin.de/) is placed in a subsystem which has limited interaction with
the rest of the world. What would happen if ...
-2
votes
0answers
27 views
Finding Clebsh-Gordan coefficient [closed]
Two electrons , their angular quantum number =1 . Find the inner product of < 2 0 | 00 > ?
6
votes
2answers
376 views
$\nabla ^2\psi$ equals $\psi -$ average value of $\psi$ at neighboring points
Let $\psi (x,y,z)$ be a scalar field. I found the following statement in Morse & Feshbach Methods of Theoretical Physics:
The limiting value of the difference between $\psi$ at a point and the ...
1
vote
1answer
66 views
Basic energy calculation for N identical spin system
We have a system that has N identical spins $n_i$, and each spin can be in state 1 or 0. The overall energy for the system is $\epsilon\sum_{i=1}^{N}n_i$.
My understanding: There is only one ...
0
votes
1answer
37 views
Relative Velocity problem
I was solving many problems on relative velocity and observed that when the question asks,
"what is the minimum time taken by the boat/man to cross the river.?"
so the solution says that he ...
0
votes
1answer
24 views
Kinetic energy when $F(t)$ graph is given
The very basic problem here is that the point where this graph ends is ambiguous. I mean, what is the corresponding $y$-value for the point whose $x$-valu is $4.5s$? Then I think we should find the ...
4
votes
4answers
331 views
Which gets you first when you are falling into a black hole, the black hole singularity or the cosmic background radiation?
If you look up while you are falling into a black hole you see the universe blue shifted, that is, you see the universe moving quickly forward in time compared to your local time. Since this effect ...
1
vote
1answer
456 views
Finding electric power generated using heat transfer
I'm working through an example I have been given to study. Suppose I have a 2m X 4m photovoltaic panel on my roof that is irradiated with a solar flux of $G_s = 700W/m^2$.
Given:
$\alpha_s = 0.83$
...
0
votes
6answers
179 views
Inertial Frames of Reference - Inertial vs. Accelerated Frames
According to Robert Resnick's book "Introduction to Special Relativity", a line states the following as the definition of an inertial frame of reference: "We define an inertial system as a frame of ...
0
votes
2answers
36 views
Isothermal Gas Expansion, a Reversible or Irreversible process?
Consider the following situation. A certain quantity of ideal monatomic gas (say one mole) is confined in a cylinder by a piston and is maintained at constant temperature (say $T_0$) by thermal ...
0
votes
0answers
19 views
How to make a fan like behavior [migrated]
I am making a game in Unity. I have an object e.g. cube. I want to release air from it like fan so that when other cubes come closer, it throws them away. What velocity,force etc I will need to do ...
-1
votes
0answers
18 views
Probability distributions [migrated]
What is the probability that a random number [0,1) will lie in [0.5,0.6]?
As far as I know, there are 3 probability distributions in physics we usually use, but I am not sure when we can use ...
-1
votes
0answers
29 views
What values should the solved time-independent Schrodinger equation return? [closed]
I'm doing a project on Schrodinger's equation for my differential equations class. We solved the time independent function, and now we want to provide some examples of applying the equation by solving ...
0
votes
1answer
60 views
Electric Field in Circular waveguide in TE mode
I know that the magnetic field inside a circular waveguide is
$B_z=B_0\dfrac{\rho}{R}\left(1-\dfrac{\rho}{2R}\right)\cos{\phi}\sin{\frac{\pi z}{d}}$
How can I find the two components of the electric ...
0
votes
1answer
39 views
Eigenvalue $a_n$
Q1:
In Zetilli's book page 166 (ch. "Postulates of QM", eq. 3.1) i encountered an expression $\hat{A}|\psi\rangle = a_n|\psi_n\rangle$. I know this is an eigenvalue equation, but i have seen another ...
0
votes
1answer
15 views
Convergence of Light on the Retina
So, I've learned about lens ray diagrams-but the problem I'm having is that when ray diagrams are drawn for a point of an image, they converge to another point, but there are two problems that I see ...
3
votes
1answer
112 views
Is it possible to determine particles' velocities from their crossings on a ring?
2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
11
votes
2answers
192 views
How large can planets or moons appear?
In many artistic impressions or movies there are pictures or scenes where the sky is filled with an enormous moon (as seen from a planet) or vice versa.
I wonder if there is an upper limit to the ...
0
votes
1answer
27 views
A Calorimetry Problem
I have a question in calorimetry from an old competitive exam. The question is:
The temperature of $100$ grams of water is to be raised from $24 ^\circ$C to $90 ^\circ$C by adding steam to it. ...
1
vote
1answer
31 views
How does tension apply torque on a pulley?
How is tension in a string able to apply torque on a string? How does string itself able to apply a force on pulley? What is happening inside the pulley?
The pulley has a mass m and is a disc .
0
votes
1answer
160 views
Deceleration of Vehicle off pavement
How would I calculate the deceleration of a vehicle (ATV), wheels locked, on dirt? How long would it take to halt? How fast is it decelerating?
I used this calculator, but it seems incorrect for a ...
1
vote
2answers
45 views
Electric potential energy after nuclear fission
We have a uranium-236 nucleus that fissions into two equal fragments, and I'm supposed to find the electrical potential energy just as the two fragments split apart. No other information is provided.
...
7
votes
5answers
134 views
Physical representation of volume to surface area
I was looking at this XKCD what-if question (the gas mileage part), and started to wonder about the concept of unit cancellation. If we have a shape and try to figure out the ratio between the volume ...
2
votes
1answer
67 views
Convert a 200mm linear stroke into 90 degrees motion
Can anyone help me Convert a 200 mm linear stroke into 90 degrees motion with as much mechanical advantage as possible or into two 90 degrees motions with as much mechanical advantage as possible?
...
3
votes
1answer
101 views
Inflation and scalar spectral index
I've been reading that the results from the Planck satellite constrain a number called the "scalar spectral index" to be 0.96 rather than 1 at the 5-sigma level.
This is supposed to be big news, but ...
-3
votes
0answers
44 views
If air contains oxygen and nitrogen, why won't these two elements form water? [closed]
If air contains oxygen and nitrogen, why won't these two elements form water?
Shouldn't these two elements react and form water? Why do they stay seperated?
0
votes
1answer
21 views
Doubt in problem regarding resistance a of cylinder
I've been working on some exercises and I'm in doubt if my procedure with this one is correct. We have a hollow cylinder with internal radius $r_a$, external radius $r_b$, resistivity $\rho$ and ...
2
votes
1answer
50 views
Questions about the Jeans length
I have a couple of questions about the Jeans length. Suppose the universe has a homogeneous energy density, except there's a spherical region that is overdense.
I understand that if the region is ...
2
votes
1answer
47 views
Is there a one-to-one relationship between colour theories and our trichromatic vision?
This has started to bug me more and more… it involves:
colour theory
the trichromatic properties of our eyes through cone cells
and light.
Is there a one-to-one relationship between colour ...
2
votes
2answers
24 views
How would a change in ambient temp affect a radiator?
I'm curious if you have a radiator or say a block of metal (lets say it's copper since it has the highest thermal conductivity) and on one side is a processor producing heat.
At idle the processor ...
