All Questions

2 views

From the photons perspective

Probably been answered but couldn't find the answer. From the perspective of a photon: - For the photon to travel from body A to body B would take 0 secs. - The universe would be one point in ...
15 views

Gravity inside the Earth

Calculate the gravitaional potential $U(r)$ inside the earth. Let $r_e$ be the earth radius, $m_e$ the earth mass, $\rho$ be the earths density (equally distributed mass assumed), $G$ the ...
15 views

What is the potential difference between a and b in this basic circuit, when the switch is open?

My professor says the potential difference between a and b is the difference between the voltages on the top left capacitor and the bottom right capacitor. My friend and I however both think it's ...
24 views

I have been exposed to the usual treatment about spontaneous symmetry breaking in the standard model but it shames me to admit that there are some loose ends I still have to tie up. For simplicity, ...
13 views

Massless scalar $\phi^3$ tree-level scattering amplitudes?

The CHY formula for massless scattering at tree-level can compute i.e. scalar, gluon and graviton amplitudes. For gluon scattering there are many other resources available to compute all kinds of ...
22 views

Rocket altitude

I have a model rocket I'm planning to launch. I heard from someone that you can calculate the altitude by timing the rocket from the time it takes off to the time it lands. Does anyone know how to do ...
11 views

Moment of area and centroid

What actually is moment of area? I know area into distance definition but what is its physical interpretation.When I say moment of area of two objects are different then what the difference I eill see ...
16 views

Does any ordinary object emit radiation due to Unruh effect and equivalence principle? [duplicate]

I am just wondering is there Hawking radiation for any object (that has mass) due to its gravity. Base on the Unruh effect and equivalence principle, any object should emit Black-body radiation or ...
26 views

Assignment : Electromagnetic Fields [on hold]

Please help in resolving these questions and THANKS Uniform line charges of 5nC/m are located in free space at x=1m, z=1m; and at y=1m, z=0. Obtain an expression for D in Cartesian coordinates at ...
36 views

Why does the mass on the cart-pole have to fall?

Not sure if I am posting this question in the correct community, as it relates primarily to reinforcement learning. Apologies early on if this is not so. In reinforcement learning many algorithms ...
22 views

How does Bernoulli's principle produce wing lift? [duplicate]

In the Ray Kurzweil's book How to create a mind is said that: The mathematics of how Bernoulli's principle produces wing lift is still not yet fully settled among scientist [...] What does ...
49 views

Why is the trajectory of the alpha particle in a cloud chamber almost straight?

This question baffled me since high school. Presumably, the alpha particle has collided with macroscopically large number of molecules when it makes a macroscopically large displacement. One would ...
14 views

Solve the problem of Horizontal cylinder bar [on hold]

I want to solve the following problem. Could anyone help me to solve it. I have attached a picture of the problem. Thank you. Solve the problem of Horizontal cylinder bar
25 views

Electric field 2 half lines

The 2 semi lines split on O by angle phi constant, each line have charge density landa , i want to calculate E (M) where OM=x this is not homework , im self studying well i tried the following ...
11 views

Help to find a simple setup for optical surface topography

I'm looking for some help from someone expert in optics to create an inteferometry based setup to map the surface of a small object. This is for a small lab project so I'm not looking for a really ...
20 views

Speed of AC and DC current

If AC current oscillates as it passes through a conductor is it slower than DC current which does not oscillates?
35 views

The effect of 8 hours 20 degrees C sunshine on the temperature of a stationary car's engine block? [on hold]

What temperature of the engine block could be achieved by parking a car (Mazda 3) in full sunlight and facing south all day. Average day temperature 20 degrees Celsius no wind. And then how long to ...
34 views

Looking for a specific theory concerning Dark Matter

I am looking for the name of a theory positing that "empty" space itself is not empty, but has substance, and that "fabric" or "substance" is actually what we call Dark Matter. In theory, dark matter ...
24 views

Why superconductor have vortex

Sorry guys I really don't understand the idea of vortex in superconductor, why superconductors type II have vortices ? Thanks in advance!
30 views

What does a long half-life imply? [on hold]

If an element has a long half-life then, what can we say about the rate at which it decays? Thank you.
26 views

Does the current in a resistor depend on the speed of electrons?

If the speed of electrons in resistor is slow, then will the current be slow and if the speed of electrons is fast, then will the current be fast? Does the current in a resistor depend on the speed of ...
47 views

Inserting the resolution of identity correctly

In a text on path integrals, I find the following: \langle q_{j+1}|e^{-i(\hat{p}/2m)\delta t}|q_j\rangle = \int\frac{dp}{2\pi}\langle q_{j+1}|e^{-i(\hat{p}/2m)\delta ...
26 views

Difference between mechanical modes and phonons

As stated in this review article: Mechanical modes are long compared to the interatomic spacing. It is natural to make the distinction between nanomechanical modes and phonons: The former are ...
28 views

In which experiments the charge to mass ratio of proton was determined?

Are there experiments where the charge to mass ratio for protons have been determined in the same way as in Thompson’s experiments (where he determined the charge to mass ratio of electron) but with ...
5 views

References on particle cooling

I am looking for references on the topic of particle and mechanical oscillators cooling, in particular: Doppler cooling Resolved sideband cooling and Lamb-Dicke regime Stokes and anti-stokes modes ...
26 views

Is negative energy(work) less than positive energy(work)?

We cannot talk about magnitudes in case of work, but if someone did (-42 J of work) by stopping a moving object. And if someone did 42 J of work, by pushing something, who did more work? Does it ...
28 views

What happens when a contracted object going at speeds comparable to light is fit in a tight space, but has been brought to rest

What happens when a rod of length L moving at a speed comparable to the speed of light, is made to fit in a space of length say 3/4*L and is brought to rest. Does it exert some force on the walls ...
24 views

Regarding law of conservation of energy

what will happen in a vacuum when an object is dropped in moving van(completely closed) and when same object is dropped outside the moving van? what will be its final position in both the cases in ...
16 views

Does frame dragging apply to linear motion?

Firstly I will admit I do not understand the cause of rotational frame dragging. https://en.m.wikipedia.org/wiki/Frame-dragging In order to better understand the mechanism, I would like to know if ...
15 views

Why is the energy lost due to the internal resistance always equal to $(1/2)CV^{2}$ in a simple capacitor battery circuit? [duplicate]

Suppose we have simple circuit in which a battery of EMF $E$ is connected to a capacitor of capacitance $C$. Work done by battery $W_{b}=CV\times V$ and energy stored in capacitor ...
58 views

Modern explanation of the Young experiment with Quantum Field Theory?

In the Young double slit experiment it is possible to detect the arrival of individual photons as well as an interference pattern. It doesn't makes much sense to me that something could be either a ...
103 views

Is the reaction force for a stone hitting a wall infinite?

Let us assume a rigid stone which moves in empty space with a constant speed of $v$. (Or in the air with no friction and drag or you can imagine a free fall with friction). This stone hits a rigid ...
25 views

Difference between DMRG(density matrix renomalization group) and MPS(matrix product states)?

I am learning DMRG recently. I noticed there are many papers both in the DMRG approach and MPS(such as variational matrix product state(VMPS) by F.Verstraete and J.I.Cirac) approach. In my eyes, there ...
19 views

How to calculate turning acceleration from a compass? [on hold]

I have degree and timestamp and want to calculate the turning acceleration. I what to trigger some code when the compass is turning fast. Is there a mathematic way to get an turning acceleration ...
21 views

Motion of parallel-incoming particles in gravitational field [on hold]

There is a large parallel beam of incoming particles with mass $m$ and uniform velocity $v_0$ ($v_0 \ll c)$ in the presence of a gravitational field of a (spherical) planet with mass $M$ and radius ...
23 views

anatomy of combustion

I don't understand how energy is released in combustion. We have a reaction of a combustible material with oxygen and this releases energy. In what form is this energy released? It should be some ...
17 views

Force on a charged particle due to an uncharged infinite conducting plate

How can I calculate the force on a charged particle due to an uncharged infinite conducting plate? If there is a small object with positive charge placed above a metal plate, the object induces a ...
20 views

Why does emf of a cell equal to $\frac{F_b d}{q}\;?$

In Concepts of Physics by H.C.Verma, it is written: Some internal mechanism exerts forces on the charges of the battery material. ... We show the force on a positive charge $q$ as $\vec F_b\; .$ ...
44 views

If Gravity acts on the particles in the gas, why don't they accumulate on the lower surface and fall down?

A quantity of gas is enclosed in a metal cylinder fitted with a piston. There are very many gas molecules.The cylinder walls are thermally conducting. Now, the question...
52 views