2
votes
0answers
72 views

Integral curves in null hypersurfaces [closed]

Let be $(M^{n+1},g)$ a spacetime (Lorentz manifold, connexe and time-oriented), $n\ge 2$, and $S\subset M$ a null hypersurface (codim $S=1$ and the restriction of $g$ to each tangent space $T_p S$ is ...
0
votes
1answer
15 views

Local nuclear magnetic field compared to macroscopic field

In an NMR experiment, I the local magnetic flux density of an iron sample was found to be roughly 33 T, by checking for a resonance frequency of the magnetic dipoles. How can it be that such a high ...
1
vote
1answer
71 views

Why can center of mass be used in calculating gravity?

Why can gravitational forces be based on the center of mass. Due to the fact that gravity is related to the square of the distance should not the gravitational sum of every particle exceed the force ...
0
votes
1answer
66 views

A question on the Dirac equation

In Quarks and Leptons by Halzen and Martin p. 105 it says: The bonus embodied in the Dirac equation is the extra twofold degeneracy. This means that there must be another observable which commutes ...
2
votes
1answer
107 views

Cause of magnetic dip on Earth

How is the magnetic dip (or inclination) caused on Earth?
-1
votes
1answer
43 views

Centripetal Force [closed]

What is the size of the force required to cause a car of mass $1.75\times10^3$ kg to travel in constant circle of diameter $25.0\space m$ with a constant speed of $25.0 \space ms^{-1}$ ?
3
votes
1answer
102 views

Thought experiment on space curvature due to gravity

Let's say you built a huge, straight rigid beam out in space, far from the sun (outside the orbit of Pluto). It is very long, say 200,000 miles long, but can be very narrow. Then you move it to the ...
1
vote
0answers
95 views

What are the implications of integrating the Poisson bracket? [closed]

Reading Ref. 1 I admit I am a little lost in some places. I was hoping that someone in this area could explain the basic premise of integrating the Lie bracket and further is it connected to nlab's ...
-2
votes
1answer
71 views

Why aren't we all moving at the speed of light relative to photons? [duplicate]

Using basic logic.... We know speed and velocity is relative. My point is if we take our speed with respect to a photon moving in opposite direction we are practically moving at speed greater than ...
0
votes
0answers
49 views

How to integrate over a circle in sperical coordinates

I have an angular distribution $\frac{s \sigma}{d\Omega} = \frac{d\sigma}{d \left(\cos\theta\right) d\phi}$. How can I calculate it over a circle which lies on the plane $X = dist$, has radius $r$ and ...
0
votes
0answers
20 views

poisson noise - physical model

I have a small puzzle regarding a following physical model. There is a proton detector which can measure a noise caused by exposing it to flux of protons. From mathematical point of view I can ...
0
votes
1answer
280 views

Does diffraction take place in Young's double slit experiment?

In diffraction experiments interference takes place along with diffraction? Does diffraction take place in Young's double slit experiment? If it does take place then why don't we get the pattern of ...
1
vote
0answers
40 views

Will the flash light accelerate in space? [duplicate]

As we know from school physics course light has pressure. So my question is will flash light accelerate in space in the direction opposite to light emission? If not, then will flash light with ...
0
votes
0answers
38 views

Uncharged metal rod brought near a charged electroscope. Why does divergence of the leaves decrease?

Could someone please explain the redistribution of charges (if any) in a charged conductor that is being used to induce charge on another conductor?
0
votes
1answer
36 views

Isobaric process confusion

How does the pressure remains constant during isobaric expansion/compression despite of giving/taking heat to/from the system? I am having a confusion to understand. How does this process actually ...
0
votes
3answers
109 views

Why is the universe expanding while its components actually attract each other?

First of all, what's the difference between gravity & gravitation? Anyway that's not the actual question. If every matter attracts each other toward itself, then wasn't the universe supposed to be ...
1
vote
0answers
52 views

Lining up fans in a row

Im new to this website, and not extremely educated in the world of physics. I have a very basic (mostly high school, some college) understanding of physics. That being said, I work for the fire ...
20
votes
5answers
2k views

0 Kelvin body moving

As many books say: Temperature is (proportional, almost, etc...) average kinetic energy of particles. My question is this. "Suppose there is a body somewhere in empty space which moves at ...
0
votes
1answer
81 views

How Quantum Fourier Transform equal to Hadamard Transform on 4-by-4 matrix?

I just don't understand why $QFT_4$ become the same as Hadamard Transform $H_4$ The Hadamard matrix is as follwoing, $$ H_2 = \frac12 \begin{pmatrix} 1 & 1 & 1 & 1 \\ 1 & -1 & ...
1
vote
1answer
96 views

Equations of motion for double spherical pendulum simply?

I am attempting to simulate a double spherical pendulum, i.e. a combination of the spherical pendulum and the double pendulum. I understand that the equations of motion can be derived via the ...
0
votes
1answer
77 views

Why do objects change its direction when their velocity reaches 0?

When you throw an object into the air, the object will decelerate by 10 or 9.8 meters per second per second due to gravity. When the object reaches its highest point, the objects velocity would be ...
5
votes
2answers
172 views

Derivation of momentum in QFT - from Energy-Momentum Tensor [closed]

The conserved 4-momentum operator for the complex scalar field $\psi = \frac{1}{\sqrt{2}}(\psi_1 + i\psi_2)$ is given in terms of the mode operators in $\psi$ and $\psi^{\dagger}$ as $$P^{\nu} = \int \...
1
vote
1answer
62 views

Time dilation on Satellites due to GR

I am trying to determine the time dilation onboard a satellite (say GPS @ 20,000km) w.r.t an observer on the earth. I have already determined the special relativity component using: $$ t' = \frac{t}{\...
1
vote
0answers
18 views

do gravity shows its effect in atomic level? [duplicate]

how much of a effect do gravity shown in atomic level. how significant or negligible is it. i am guessing the effect is small because the mass of nucleus and electron is small. But the distance ...
2
votes
1answer
100 views

Smallest possible size of nuclear reactor [closed]

I recently began playing Fallout 4 and asked myself a question: Would it be possible to build a power armor with todays technology? I did some investigation on servomotors and stuff and came to ...
1
vote
0answers
51 views

Hammer will fall faster than the feather on the moon. 10 second thought experiment! [duplicate]

Please explain where my logic is wrong. a) Ignoring air, the same bowling ball will fall faster on Earth than on the Moon. b) Now, for the feather and hammer on the Moon, reverse your point of view ...
1
vote
1answer
95 views

Is entropy increase in disorder or 'energy-dispersal'? [duplicate]

My teacher explained entropy like this: It is increase in disorderliness. Take a glass jar put three layers of blue marbles in it then put three further layer of red marbles, now shake the ...
0
votes
2answers
89 views

Given force as function of position, find the total energy as function of time [closed]

Given that the force for a non-linear spring connected to a mass $m$ sitting on a table is $$f(x) = -kx -ax^3,$$ Find the total energy as a function of time $E(t)$. I have no clue where to begin.
0
votes
1answer
193 views

How do you calculate theoretical ratios of angular velocity final and angular velocity initial? [closed]

I'm asked to calculate the "Theoretical Ratio". ($\omega_f/\omega_i$) I have Inertia of the Disk = $I_{DISK} = .0094115713$, I have Hoop Inner Radius = $I_R = 55.725$ So I am supposed to use the ...
0
votes
0answers
45 views

What will the point of view be when you move faster than light in a medium?

In water the light become slower to the point where electron in water moving faster than light (in the same medium). So in electron frame of reference what will electron's point of view be? From what ...
1
vote
2answers
65 views

What depth should water be filled to in a cylinder flask to make it the most stable

As said in title, a cylinder flask with a mass of 100g and radius of 3 has a center of balence 10cm above the base. Assuming negligible wall thickness, to what depth should water be added to this ...
0
votes
2answers
126 views

Does really a spring compresses placed between two blocks when one block is given force on a frictionless surface?

When Spring is placed between two bodies on a frictionless surface it gets compressed when one block is given kinetic energy as told by my physics teacher. But it should not compress as there's no ...
3
votes
5answers
176 views

The use of electrons in synchrotrons

I'm researching synchrotrons for a class project, but I can't seem to find a decent answer to one of my questions. It appears that most synchrotrons use electrons as opposed to some other charged ...
-1
votes
3answers
58 views

Why are measurements standardized the way they are?

Using meters as a base length, squaring or cubing lengths smaller than 0.67m makes the square term larger than the cubed term. This fact causes certain properties of physics (how rain needs to form?) ...
2
votes
0answers
44 views

What kind of cheap, available, magnetic metal could I use for my boardgame? [closed]

My question revolves around my need to snap plaster walls to plaster dungeon floors for a boardgame called Dungeons & Dragons. My intention is to glue and paint over metallic strips under the ...
3
votes
3answers
164 views

Double slit: why don't the edges of the slit constitute a measuring device?

The usual explanation is that any interaction with a 'classical' system will collapse the wave function and destroy the interference pattern. So, a recorder which is left on but never observed, will ...
2
votes
2answers
122 views

Why is the acceleration due to gravity $g$ quoted as if it were constant?

In elementary physics courses the value $g=9.8\:\mathrm{m/s^2}$ is used almost universally. But surely this value must depend to some extent upon one's location on the Earth. Why do we assume a ...
1
vote
1answer
48 views

Single fluid simulation algorithm

Every fluid simulation I've seen implicitly involves a fluid that isn't mentioned, usually air. This is clear because the simulation usually has an ambient temperature, and always an ambient velocity. ...
5
votes
1answer
89 views

Nonabelian global symmetries, $SO(N)$ charges in terms of creation and annihilation operators

Consider an $SO(N)$ symmetric theory of $N$ real scalar fields,$$\mathcal{L} = {1\over2} \partial_\mu \Phi^a \partial^\mu \Phi^a - {1\over2} m^2 \Phi^a \Phi^a - {1\over4} \lambda (\Phi^a \Phi^a)^2.$$...
2
votes
1answer
98 views

calculation of electrical power required drive a toy car [closed]

i wanted to put a electrical motor into a toy car. i want to use an optimum motor with correct RPM (i know that with fixed power, higher RPM mean less torque). so here it goes. i have a toy car with ...
3
votes
1answer
35 views

Search for unpublished note on Magnetic Monopole Detection

Design of an electromagnetic detector for Dirac monopoles by Luis Alvarez This is an unpublished 1963 note from Lawrence Radiation Laboratory (Physics Note 470), and is heavily cited in all papers on ...
1
vote
0answers
11 views

microturbine heat loss

Would the hot combustion gasses in the millimeter-wide turbine in http://thefutureofthings.com/3063-engine-on-a-chip/ lose heat so quickly that the engine efficiency would be low? The velocity of ...
3
votes
1answer
42 views

What happens when the Kepler Space Telescope 'catches up' to Earth?

Kepler is in an earth-trailing orbit with a period of 372.5 days, so it lags behind the Earth about a week each year. Doesn't that mean that, in about 52 years, we'll meet it from the other direction? ...
1
vote
1answer
28 views

If iI have a capacitor connected to a battery can the negative charge be sent to an insulated object

If I have a capacitor permanently connected to a battery, that is lets say setting in a plastic bowl, and then run a wire from the negative of the battery to a non grounded object, say a metal can ...
0
votes
0answers
10 views

DGP model, minus one dimension

Is there a name for a theory like the DGP model, but with one fewer dimension? That is, a theory whose action consists of the 4D Einstein Hilbert action at long distances, and the 3D one at small ...
1
vote
0answers
67 views

Why are the cores of planets melted?

We all know that the core of Earth is in liquid form, as are most other planets as recently read. Why is this the case? Obviously, high temperatures are the cause, but what causes the high ...
1
vote
0answers
54 views

How does the expanding of null hypersurface orthogonal geodesic congruence imply a particular result?

Sorry that I do not know how to summarize my problem in the title. First, please go to the website here (free access, even though it looks otherwise) to download the paper done by R. Sashs on ...
3
votes
1answer
126 views

What is the meaning of the UV =? IR statement in String theory

I was looking through these notes http://www.damtp.cam.ac.uk/user/tong/string/six.pdf and on page 146 it says "This corresponds to the fact that any putative UV divergence of string theory can always ...
1
vote
2answers
58 views

Is it possible to shield a magnetic field?

Is it actually possible to shield a magnetic field? They teach us at school that magnetic fields are generated by electricity running through the wires (that's how electromagnets work). On the other ...
1
vote
2answers
336 views

Can you breakdown an atom?

Protons, neutrons, and electrons make up the atom, but I've heard that you can't breakdown an atom. How do we know that the electrons, protons, and neutrons make up the atom without being able to ...

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