0
votes
2answers
23 views

Inclined pulley with unknown hanging mass: when won't the system accelerate?

We have an inclined pulley with angle of $30° $ a block with mass of $10 kg$ placed upon it and It is attached by a rope over a pulley to a mass of $M_A$ which hangs vertically. If $μ_s=0.4$ and ...
0
votes
0answers
3 views

Gravitational time dilation, does time of the observer at a lower gravitational potential looked slowed down in the frame of the higher one

This question is mainly inspired after watching the movie known as Interstellar We knew that for time dilation caused by relativistic motion between A and B. A will measure B's clocks slowing down, ...
-6
votes
0answers
17 views

Is it possible that the universe doesn't exist?

Is it possible that the universe doesn't exist? that nothing exists, not even you or me?
0
votes
1answer
45 views

Force of a Train

Imagine that there are two trains and the first train is twice as long as the second train. They have the same mass per unit length and they are traveling at exactly the same speed. If the first ...
5
votes
3answers
995 views

How did Newton discover his third law of motion?

How did Newton discover his third law? Was it his original finding or was it a restatement of someone else's, like the first law coming from Galileo? What initiated the concept of what is now known as ...
1
vote
1answer
46 views

Describing a single photon with creation and annihilation operators

Since I am not fully aware of the creation and annihilation operator formalism for single photons, I want to ask, if the following is correct: I am considering a photon in the vacuum which travel ...
0
votes
2answers
21 views

How to actually account for air resistance?

What's interested me in my studies thus far is that in a lot of beginner undergrad mathematics and physics courses we're often told to calculate trajectories, velocities, etc. by "ignoring air ...
0
votes
0answers
13 views

Best book for learning Quantum Communication [duplicate]

I want to do my BSc thesis on Quantum Communication. So I want to learn fast. I have a brief idea about quantum computing. So please suggest me some books from which I can learn about quantum ...
20
votes
2answers
2k views

How light speeds up after coming out of a glass slab?

As I learned today in School, my teacher told me that when light enters a Glass Slab it slows down due to the change in density and it speeds up as it goes out of the Glass Slab. This causes a lateral ...
1
vote
3answers
52 views

Does quantum entanglement arise from quantum theory or is it merely an experimental observation?

I assume that entanglement emerges from quantum mechanics because the idea was around before experimental verification (e.g the EPR paper). How then does entanglement emerge from the theory (please ...
5
votes
0answers
41 views
+100

Relating momentum fraction to rapidity in a high-energy collision

It's a well-known result in particle physics that in an underlying interaction like this: assuming $p_0^-,p_{0\perp},m_0\ll p_0^+$, the rapidity ($y = \frac{1}{2}\ln\frac{p^+}{p^-}$) differences ...
0
votes
0answers
25 views

Momentum in the frame of reference of the center of mass [on hold]

I'm a high school student who just learned this topic in class today. I don't understand why the sum of momentum is zero in the frame of center of mass. Also, how can I solve this problem: Three ...
3
votes
1answer
48 views

Why do we need frame-fields to describe fermions in SUGRA?

I'm learning about the frame formalism and read that to couple fermions to gravity you need to go to the frame-formalism. As a motivation to learn more about frame-fields would someone sketch me why ...
1
vote
1answer
98 views

Why does graphene exist?

I started to read some articles on graphene and almost all say that graphene was discovered late because physicists thought it would be unstable. Despite this, I didn't found a clear explanation of ...
2
votes
2answers
73 views

Pulling on a weakened rope - where will it tear?

Let's say I have a rope of 10m length and it is weakened in 3 spots: at 2.5m, at 5m and at 7.5m. Weakened means that if enough tension is applied it will tear at these points (all points are equally ...
10
votes
2answers
2k views

Why don't we have a theory of everything?

What is currently stopping us from having a theory of everything? I.e. what mathematical barriers, or others, are stopping us from unifying GR and QM? I have read that string theory is a means to ...
0
votes
0answers
37 views

Lorentz transformations of spinors in $SL(2,\mathbb{C})$

I was wondering what the matrix representations of all the coordinate rotations and Lorentz boosts of the $SL(2,\mathbb{C})$ were along with a general method of solving for them. I've been able to do ...
6
votes
8answers
471 views

In reverse time, do objects at rest fall upwards?

I want to develop a game where time runs backwards, based on the idea that physical laws are reversible in time. However, when I have objects at rest on the earth, having gravity run backwards would ...
7
votes
3answers
2k views

Can open, unsafe nuclear fusion reaction burn the atmosphere?

I happened to hear people saying that the nuclear fusion bomb tests could set the atmosphere on fire. I have some serious doubts about that - but I have no facts. Nuclear fusion reaction requires ...
0
votes
2answers
97 views

What indicates if an object will bounce back?

If I throw a small rock (m = 1kg) at a big rock (100kg) the small rock rebounds. Let's say my weight is 80kg, if I would jump into a big rock instead of bouncing back I would move in the same ...
11
votes
6answers
325 views

Why isn't length contraction permanent even though time dilation is?

It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that ...
0
votes
0answers
6 views

Direction, closeness and range of streamlines in a flow domain with solid boundary and free surface?

I have a flow-field with solid boundaries and a free surface, I have plotted the streamlines, however I am not sure whether my graph is correct. In fact, I drew the streamlines by taking a range of ...
1
vote
1answer
61 views

Electric force between charges in two different media

As far as I know, Coulomb's law of electrostatic force is applicable on two different charges situated in same medium. But if two individual charges are in different media (say one charge on a iron ...
0
votes
0answers
8 views

How to calculate the solid-liquid interface energy knowing the surface free energy and liquid contact angle?

Given surface free energy something around 20mN/m, and the contact angle around 120° for water (73mN/m). How can I estimate the solid-liquid interface energy of the given solid surface to water? I ...
0
votes
0answers
15 views

How to minimize the wavepacket dispersion?

This is a final exam problem. Here is what I can remember: We know that if an electron's wavefunction starts out as a narrow wavepacket, and moving in a region of constant potential, then the ...
0
votes
0answers
12 views

Critical engine failure just after rotation: what percent of accelerated slipstream lift does the wing loose? [on hold]

I have searched the web for facts about the lift created by a propeller slipstream (propwash). I have found many web sites that in fact claim that the propeller slipstream does indeed produce a lift ...
0
votes
0answers
25 views

Speed of a magnet

What is the speed of two magnets during the congruent moment of their attraction? Theoretically, could a large enough magnet attract a significantly smaller magnet at near the speed of light? In ...
0
votes
1answer
37 views

Why is rho to two pions not allowed? [duplicate]

Why is the $\rho^0 \rightarrow \pi^0 + \pi^0$ decay not allowed? I have seen this question but I am not satisfied with the answers. The $J^{PC}$ of the $\rho$ and $\pi$ are $1^{--}$ and $0^{-+}$ ...
0
votes
1answer
16 views

Why is space isotropic in the vector particle's decay?

I come across one proof the Landau-Yang Theorem, which states that a $J^P=1^+$ particle cannot decay into two photons, in this paper (page 4). The basic idea is, the photon's wavefunction should be ...
1
vote
0answers
21 views

Aurora borealis forecasting, some technical details

I have an idea to make a software tool (with some really user friendly interface) for predicting auroras on any place on Earth. I do know some physics behind the phenomenon, but only basics, like it ...
5
votes
1answer
146 views

Could the same symmetry be finetuning both the Higgs mass and the inflaton's interactions?

The observed Higgs boson mass is at an interesting place in parameter space, placing the standard model electroweak vacuum right at the edge of metastability. Among the proposed explanations of this ...
3
votes
1answer
40 views

Why (and how) do foods stick to a pan?

We all (sooner or later) have noticed that foods relatively high in protein (especially those low in fat) are very prone to sticking to a pan, or in general to any non-specially-coated metal surface. ...
2
votes
2answers
52 views

Is light emitted in zitterbewegung?

Recently I heard of Zitterbewegung, a trembling motion of the electrons in atoms that arises from Dirac's equation. I know that, according to Bohr's model, light is emitted when the electron "jumps" ...
0
votes
1answer
33 views

Can diffraction be used like gravitational lensing [on hold]

I was thinking that in both the cases of diffraction and gravitational lensing, light is bend to some extent mimicking the lens effect. My Question is, Can diffraction be used like gravitational ...
3
votes
1answer
147 views

Sliding ruler on table top

I've got a standard foot-long flat plastic ruler (about an inch wide) and a desk with a smooth formica-like surface. When idly passing time reading on the computer, I will pick up one side of the ...
0
votes
3answers
4k views

Constant Velocity 'Force'?

According to Newtons second law: F = ma, if acceleration is zero then the force must be zero, but assuming you have an object moving with a constant velocity of say 2 m/s, and that object strikes you, ...
1
vote
2answers
151 views

Lippmann-Schwinger solution

What's wrong with this general solution of the Lippmann-Schwinger equation: $$ |\psi_k \rangle=|\phi_k \rangle+G_k V|\psi_k \rangle $$ Taking the inner product with $\langle\phi_{k'}|$ \begin{align} ...
1
vote
0answers
10 views

LOCAL Temperature Gradient and Stress

I'm investigating the thermo-migration failure mechanism in nanoscale ICs interconnects. Typically, a nano wire under thermal stress suffers from material/mass migration or void nucleation if it ...
0
votes
1answer
28 views

Quantum Physics, Energy States

Which of the following transitions in a hydrogen atom absorbs a photon of the highest energy? a.) $n=2\hspace{1cm}to\hspace{1cm}n=3$ b.) $n=3\hspace{1cm}to\hspace{1cm}n=2$ c.) ...
1
vote
0answers
15 views

Mutual inductance theoretically decreasing while EMF is increasing in 2 square coil system

I have a quick question regarding electricity and magnetism. I am measuring the induced emf in a square coil of wire with an inductance of 439uH (the other coil is also 439uH and is the same shape). I ...
0
votes
0answers
13 views

Calculations to Determine Force Required for Gyroscopic Stabalization

I am currently undertaking a project involving gyroscopes, the aim of which is to stabilize a large object. I have read that gyroscopes work because of conservation of angular momentum, and if you ...
44
votes
3answers
5k views

How can ants carry items much heavier than themselves?

This morning I saw an ant and suddenly a question came to my mind: how do ants actually carry items much heavier than themselves? What's the difference (in physics) between us and them?
2
votes
1answer
183 views

Large deflection of cantilever beam

How can I find the amount of point force at the end of a cantilever plastic beam that produces e.g. 45deg slop at the end of the beam? Is this the right equation: $$F=\frac{2EI\theta ^2}{L^2 ...
0
votes
0answers
16 views

Short Wave UV lamp [on hold]

if I remember correctly, shortwave UV is very dangerous such that it can break DNA apart. Today I found this site, where parent can buy some scientific tools for their kids. Do not you think shortwave ...
0
votes
1answer
71 views

Why do we always consider the area of inner solenoid while calculating the mutual inductance of two coaxial solenoids?

While we know that flux linked to an area is the dot product of the area vector of the loop(and not the actual area encountering the field lines) and the magnetic field linked to it, why then do we ...
3
votes
1answer
83 views

What does Weinberg–Witten theorem want to express?

Weinberg-Witten theorem states that massless particles (either composite or elementary) with spin $j > 1/2$ cannot carry a Lorentz-covariant current, while massless particles with spin $j > 1$ ...
4
votes
2answers
76 views

Is the charge distribution for an electric field unique?

If the electric field and boundary conditions are known exactly for a region of space, is it true that there exists only one charge distribution in that region of space that could have produced it? ...
0
votes
2answers
49 views

About the double orthogonality of the eigenfunctions of the Hamiltonian

Consider the usual Hamiltonian describing the motion of a particle, $$\hat H = \frac {\hat P^2}{2m} + V(r),$$ where for simplicity the problem can be considered in 1D on the semiaxis $[a, \infty)$ , ...
0
votes
2answers
58 views

What does amplitude in wavelength of light physically mean?What oscilates with time in photon?

Like amplitude in wavelength of water waves signify the displacement of water particles about their mean position.
12
votes
5answers
3k views
+100

Is the total energy of the universe constant?

If total energy is conserved just transformed and never newly created, is there a sum of all energies that is constant? Why is it probably not that easy?

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